Surveyor’s Chain to Feet Converter: All US Historic Survey Units
Convert between Gunter’s chains, links, rods, furlongs, varas, and feet using NIST-verified exact values. Includes the 2023 US Survey Foot deprecation update, legal description parser, and PLSS reference data.
Unit Converter mode converts any value to all 12 survey and length units simultaneously. Legal Description Parser extracts and sums chain-based distances from text like “40 chains 25 links North.”
Chain Type
Foot Definition
Input Value
All results are shown simultaneously. No need to switch dropdowns for each unit pair.
⛓
Enter a value, select the source unit, and click Convert All Units.
📊 Scale of US Survey Units (log scale)
Paste or Type a Legal Description
Supports: ch/chains, li/links, rd/rods, fur/furlongs, vara/varas, ft/feet, in/inches. Bearing directions (N, S, E, W) and other text are ignored.
📜
Paste a legal description with chain-based distances and click Parse.
Parse Results (Gunter’s Chain basis)
What Gunter’s Chain Built: America’s Original Land Measurement System
If you have ever tried to read an old deed, a county plat, or a Bureau of Land Management parcel record in the western United States, you have run into Gunter’s chain. A distance of “40 chains North to the quarter section corner” is as common in 19th-century land records as street addresses are today. The chain is not just a historical curiosity. It is the measurement unit that divided 1.5 billion acres of American land into the property boundaries that millions of US landowners depend on right now.
Edmund Gunter was a 17th-century English mathematician who designed the surveyor’s chain in 1620. He set its length at exactly 66 feet, divided into 100 links of 7.92 inches each. This specific dimension was not arbitrary. A chain of 66 feet was chosen because 10 square chains equals exactly one acre, and 80 chains equals exactly one mile. This made area and distance calculations in land surveying almost trivially simple before the age of calculators. A rectangular plot 10 chains wide and 16 chains long is exactly 16 acres. No multiplication needed once you know the system.
NIST authority: The exact conversion factor for Gunter’s chain is published in NIST SP 811 (2023 Edition) and NIST node/1582061: 1 chain = exactly 66 international feet = exactly 20.1168 meters. This is the same chain value used in all PLSS surveys since the Land Ordinance of 1785.
From the 1785 Land Ordinance to the PLSS: Why 66 Feet Controls American Property
The Public Land Survey System (PLSS) was created by the Land Ordinance of 1785, passed by the Continental Congress one year before the Constitution was ratified. The law directed that all federal land west of the Ohio River be surveyed and divided using Gunter’s 66-foot chain before it could be sold to settlers. This was not a minor administrative decision. It was the founding framework for land ownership across 30 US states and roughly 1.5 billion acres of land.
The PLSS divides land into a grid of townships, each six miles square. Each township contains 36 sections, each one mile square and 640 acres. The math works perfectly because one mile equals exactly 80 Gunter’s chains (80 x 66 = 5,280 feet), so a section is 80 chains on each side. A quarter section (160 acres) is 40 chains on each side, which is why homestead deeds so often begin with distances in 40-chain multiples.
Today, the Bureau of Land Management (BLM) maintains the PLSS cadastral survey records for all federal and many private lands. These records, along with county plat books, state archives, and title company records, still use Gunter’s chain measurements extensively. Any title attorney, land surveyor, or GIS professional working with old property records needs to be able to convert chain-based distances to modern units quickly and accurately.
Links, Rods, and Furlongs: The Complete Chain Family of Units
Gunter’s chain spawned an entire family of related units that appear throughout US land records:
Link (li): One hundredth of a chain, equal to exactly 0.66 feet or 7.92 inches. Legal descriptions often express distances as whole chains plus whole links: “32 chains 47 links.” Each link was literally one wire link in the original metal surveying chain instrument.
Rod (rd), also called Pole or Perch: Exactly one quarter of a chain, equal to 16.5 feet. The rod is a unit that predates Gunter’s chain and was incorporated into the chain system. You see rods in older colonial-era deeds and in descriptions of lot widths in town plats laid out in the 18th century.
Furlong (fur): Exactly 10 chains, equal to 660 feet or one-eighth of a mile. The word means “furrow long”: the typical length of a furrow that a team of oxen could plow without resting. Furlongs are rarely seen in US property descriptions except in some very old records, but they remain the standard unit for horse racing distances.
Engineer’s Chain: A separate 100-foot chain developed for civil engineering work (road design, sewer surveys, railroad alignment) where a round-number station interval made calculations easier. Engineers set stations at 100-foot intervals along a survey line, so distances are expressed in engineer’s chains and engineer’s links (each one foot). Civil engineering plans and some municipal utility records still use this convention.
How This Converter Works: NIST Values, Both Chain Types, and Legal Parsing
Every conversion in this calculator is based on exact values published in the 2023 edition of NIST Special Publication 811, the official US government reference for unit conversions, and NIST node/1582061 which provides the revised conversion factors for the US Survey Foot deprecation. No rounded approximations are used for the primary unit relationships.
Converting Chains to Feet: The Exact Arithmetic
1 Gunter’s Chain = exactly 66 international feet = exactly 20.1168 m
1 Link = exactly 0.66 ft = 7.92 in = 0.201168 m
1 Rod = exactly 16.5 ft = 5.0292 m
1 Furlong = exactly 660 ft = 201.168 m
This calculator converts any input unit to all 12 supported units simultaneously in a single click. You never need to switch between unit pairs: enter 40 chains and instantly see the equivalent in links, rods, feet, yards, meters, miles, furlongs, inches, varas, and the deprecated US survey foot. This all-at-once approach is unique among web-based chain converters, which almost universally show only one output unit at a time.
The US Survey Foot vs. the International Foot: NIST’s Critical 2023 Change
This is the most important recent development in US surveying practice, and no other chain converter on the web addresses it properly. On December 31, 2022, the National Institute of Standards and Technology (NIST) and the National Oceanic and Atmospheric Administration (NOAA) officially deprecated the US Survey Foot.
⚠ NIST 2023 Update: US Survey Foot Officially Deprecated
As of December 31, 2022, the US Survey Foot (1200/3937 meters = 0.3048006096… m) has been deprecated by NIST (85 FR 62698). The international foot (exactly 0.3048 m) is now the only foot for US federal surveying and mapping. The two feet differ by exactly 2 parts per million, approximately 0.01 feet per mile. For large-scale coordinate systems like State Plane, this difference accumulates to significant horizontal errors. NIST node/1582061 provides the official revised conversion factors. For historical PLSS record research, the US Survey Foot toggle in this calculator outputs legacy values for reference.
The practical impact of this change: when converting chain-based PLSS distances to feet for use in modern GIS coordinate systems (State Plane, UTM), use the international foot. When interpreting a historical deed or matching coordinates in an older CAD file that used US survey feet, the US Survey Foot toggle gives you the legacy values for comparison. The difference between the two systems is undetectable on a single parcel but compounds to 12.9 feet per million feet of State Plane coordinate difference in some states, as documented by Esri’s ArcNews analysis of the NIST change.
Legal Description Parser: Extract Distances from Text
The Legal Description Parser tab accepts free-form deed text and extracts all distance measurements in chain family units. For a call like “North 42 chains 15 links to an iron rod marking the Northeast corner,” the parser extracts “42 chains” and “15 links,” converts both to feet, adds them, and outputs the total in feet, chains, and miles. This saves the manual arithmetic that title researchers and GIS technicians perform dozens of times per day when digitizing historic survey records.
Supported units in the parser: chains (ch, chain, chains), links (li, link, links), rods (rd, rod, rods, pole, poles, perch, perches), furlongs (fur, furlong, furlongs), varas (vara, varas), feet (ft, feet, foot), and inches (in, inch, inches). Bearing calls (N, S, E, W, NE, etc.) and other text are ignored automatically.
Complete US Survey Unit Reference Table with NIST Exact Values
The following table presents all conversion factors from NIST SP 811 (2023) and related NIST publications. These are the exact or near-exact values used inside this calculator. Where a value is marked “exact,” it carries no rounding uncertainty.
Unit
Symbol
Int’l Feet (exact)
Meters (exact)
Notes
Link
li
0.66 ft
0.201168 m
Exactly 0.66 ft; 100 links per chain (NIST SP 811)
Rod / Pole / Perch
rd
16.5 ft
5.0292 m
Exactly 16.5 ft = 4 rods per chain (NIST)
Gunter’s Surveyor’s Chain
ch
66 ft
20.1168 m
PLSS standard since 1785; exactly 66 ft (NIST SP 811)
Engineer’s Chain
ech
100 ft
30.48 m
Civil engineering surveys; 100 engineer links of 1 ft each
Furlong
fur
660 ft
201.168 m
Exactly 10 chains = 1/8 mile (NIST SP 811)
Statute Mile
mi
5,280 ft
1609.344 m
Exactly 80 chains = 8 furlongs (NIST)
Yard
yd
3 ft
0.9144 m
Exactly 3 ft
International Foot
ft
1 ft
0.3048 m (exact)
Current US standard since 1959; NIST SP 811
US Survey Foot (deprecated)
ft-us
1.0000020017 ft
1200/3937 m
DEPRECATED Dec 31 2022 by NIST (85 FR 62698)
Inch
in
0.08333 ft
0.0254 m
1/12 ft exactly
Texas Vara
vara
2.7778 ft
0.846668 m
Approx 33.333 in; Spanish land grants in TX, CA, NM
Meter
m
3.280839895 ft
1 m
SI base unit; 1 m = 1/0.3048 ft (from intl foot definition)
Area Units: Chains to Acres and PLSS Sections
Area Unit
Square Feet
Chains
PLSS Significance
Square Link
0.4356 sq ft
0.0001 sq ch
Smallest practical PLSS area unit
Square Chain (sq ch)
4,356 sq ft
1 sq ch
0.1 acre; 10 sq chains = 1 acre
Rood
10,890 sq ft
2.5 sq ch
0.25 acre; rare in US but appears in old deeds
Acre
43,560 sq ft
10 sq ch
PLSS fundamental area unit; 10 chains x 10 chains
Quarter Section
6,969,600 sq ft
1,600 sq ch
160 acres; 40 chains x 40 chains (Homestead Act unit)
Section
27,878,400 sq ft
6,400 sq ch
640 acres; 80 chains x 80 chains = 1 sq mile
Township
1,003,622,400 sq ft
230,400 sq ch
36 sections; 480 chains x 480 chains = 36 sq miles
The Texas Vara: Spanish Land Grant Unit Still Used in Title Records
The vara is a Spanish unit of measurement that was the legal standard for land surveys in Texas, California, New Mexico, and other territories that were part of the Spanish Empire and later Mexico before US acquisition. In Texas, the vara is defined as approximately 33.333 inches (one-third of a braza), though the exact value varies slightly by historical Spanish province. The most common US title reference value is 33.333 inches = 2.7778 feet. Old Spanish land grant boundaries in South Texas, San Antonio, and the Rio Grande valley still use vara measurements in their original legal descriptions, and these sometimes appear in oil and gas leases, easement descriptions, and property dispute documents.
Three Real US Land Records: Chain Conversions from Actual Deed Research
The following examples illustrate how chain unit conversions appear in real US property research scenarios across three PLSS states. These are the types of calculations that title examiners, land surveyors, and GIS technicians perform regularly when working with historical land records.
📍 Billings, Montana
Homestead Patent Legal Description
A 1912 BLM homestead patent for the Southwest Quarter of Section 14, Township 1 North, Range 26 East describes the parcel as: “Beginning at the Southwest corner; thence North 40 chains; thence East 40 chains; thence South 40 chains; thence West 40 chains to the point of beginning.” GIS analyst needs to build a polygon in State Plane Montana coordinates.
Each side: 40 chains x 66 ft/chain = 2,640 ft = 0.5 miles. Area: 40 ch x 40 ch = 1,600 sq chains = 160 acres. Each corner coordinate offset: 2,640.00 international feet (NOT 2,640.05 US survey feet, after NIST 2022 deprecation). Using wrong foot type creates a 0.05-ft per side error.
📍 Medford, Oregon
Timber Cruise Tract Boundary
A forestry company’s timber cruise record from 1955 describes a tract boundary using Oregon DOT control: “North 12 chains 47 links along the section line to an iron pipe at the Northwest corner.” The land title company needs this in feet for a CAD overlay.
12 chains: 12 x 66 = 792 ft. 47 links: 47 x 0.66 = 31.02 ft. Total: 823.02 international feet. Parser tab gives this in two seconds: paste the description text, click Parse, read 823.02 ft from the result.
📍 Laredo, Texas
Spanish Land Grant: Vara Conversion
A Webb County abstract of title for a South Texas ranch includes a Spanish land grant metes-and-bounds description from 1804 in varas: “Norte 2,400 varas to the Northwest corner.” The title examiner needs to convert to feet and meters for a survey comparison.
2,400 varas x 2.7778 ft/vara = 6,666.67 feet = 100.76 chains (Gunter’s) = 1.2626 miles. In meters: 2,400 x 0.84668 = 2,032.03 m. Enter “2400” with vara selected in the converter to get all equivalents instantly.
Six Tips for Working Accurately with Historic US Survey Units
1
Always Confirm Which Chain Type a Document Uses
Before converting, confirm whether the source document uses Gunter’s chain (66 ft, used in all PLSS work) or Engineer’s chain (100 ft, used in road design and municipal surveys). A 40-chain distance is 2,640 ft in PLSS deeds but 4,000 ft in an engineer’s survey. Confusing the two doubles or halves your distance. The document context (PLSS section, homestead, road survey) is usually the best clue.
2
Use International Foot for Any New GIS or CAD Work
Since December 31, 2022, NIST requires the international foot (exactly 0.3048 m) for all new US federal geodetic work. If you are loading chain-based distances into ArcGIS, Civil 3D, or any coordinate-based software, use international feet. The 2 parts-per-million difference between international and US survey feet compounds to roughly 10.6 feet per million feet of State Plane coordinate, which matters for infrastructure mapping and property boundary work at county or regional scale.
3
Check County Plat Archives When PLSS Calls Don’t Close
If a chain-based legal description does not close when you plot the calls in GIS, the most common causes are: (1) a transcription error in the link count (47 links vs. 74 links are easy to swap in handwritten records), (2) a bearing error (S vs. N), or (3) a foot-type mismatch between old US survey foot coordinates and modern international foot GIS datum. County recorders, the BLM’s General Land Office plat records at glorecords.blm.gov, and state archive offices hold the original survey field notes that resolve these conflicts.
4
Add Chain Distances Before Converting, Not After
When a description has multiple chain-family calls (“42 chains 15 links”), always add them in the same unit before converting. Convert 42 chains to links (4,200 li), add 15 links (4,215 li), then convert to feet (4,215 x 0.66 = 2,781.9 ft). Converting separately and adding introduces rounding errors. The Legal Description Parser in this calculator handles this correctly: it converts each component to feet using exact NIST values before summing.
5
Remember the Vara Is Not Standardized Nationally
Unlike chain, link, and rod (all exactly defined by statute), the vara was never uniformly standardized across the American Southwest. Texas uses approximately 33.333 inches. California used 33 inches in some districts and 33.372 in others. New Mexico had its own local standard. When working with Spanish land grant documents, always check the specific state or district vara definition for the jurisdiction. When in doubt, use the value stated in the original survey notes if available, or consult the state land office.
6
Preserve Chain Notation in Historical Document Transcriptions
When digitizing historical deeds and creating GIS attribute tables, always preserve the original chain-based distance in a separate field alongside the converted feet value. Writing “823.02 ft” without recording the source “12 chains 47 links” loses the ability to verify the conversion and check against the original document later. Surveyors, title examiners, and historians may need to re-examine the source description, and having both values in the record eliminates ambiguity about which foot definition was used in the conversion.
Which States Use the PLSS and Where Chain Conversions Matter Most
The PLSS applies to land in 30 US states. These states contain the bulk of the land records where Gunter’s chain measurements are encountered in legal descriptions, plat maps, deed books, and BLM land status records. States shown with darker borders in BLM mapping are those where PLSS is the primary cadastral survey system.
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Florida
Idaho
Illinois
Indiana
Iowa
Kansas
Louisiana
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Mexico
North Dakota
Ohio
Oklahoma
Oregon
South Dakota
Utah
Washington
Wisconsin
Wyoming
Source: Bureau of Land Management PLSS program. Note: Texas, the original 13 colonies, Hawaii, and several other states use metes-and-bounds or other survey systems and do not have PLSS coverage, though some Texas land records still use chain measurements from the Spanish/Mexican era.
Quick Reference: All Survey Unit Conversions in One Table
This table provides the most commonly needed chain-family conversions for title research, GIS work, and field surveying. All values use international feet per NIST SP 811 (2023).
From
To Feet
To Meters
To Chains (ch)
To Links (li)
To Rods (rd)
1 Link
0.66 ft
0.201168 m
0.01 ch
1 li
0.04 rd
1 Rod
16.5 ft
5.0292 m
0.25 ch
25 li
1 rd
1 Chain (Gunter’s)
66 ft
20.1168 m
1 ch
100 li
4 rd
1 Furlong
660 ft
201.168 m
10 ch
1,000 li
40 rd
1 Mile
5,280 ft
1,609.344 m
80 ch
8,000 li
320 rd
1 Quarter Sec. side
2,640 ft
804.672 m
40 ch
4,000 li
160 rd
1 Section side
5,280 ft
1,609.344 m
80 ch
8,000 li
320 rd
1 Township side
31,680 ft
9,656.064 m
480 ch
48,000 li
1,920 rd
1 Texas Vara
2.7778 ft
0.84668 m
0.04209 ch
4.209 li
0.16836 rd
1 Engineer’s Chain
100 ft
30.48 m
1.5152 ch
151.52 li
6.0606 rd
1 Meter
3.28084 ft
1 m
0.04971 ch
4.971 li
0.19884 rd
1 US Survey Foot (depr.)
1.0000020017 int’l ft
0.3048006096 m
0.015152 ch
1.5152 li
0.06061 rd
Frequently Asked Questions About US Surveying Units and Chain Conversions
One Gunter’s surveyor’s chain equals exactly 66 international feet, as defined in NIST SP 811 (2023 Edition). This is not an approximation: the chain-to-foot relationship is exact by definition. One chain also equals exactly 100 links, 4 rods, and 20.1168 meters. The chain was set at 66 feet because it makes acre arithmetic simple: 10 square chains equals exactly one acre, and 80 chains equals exactly one statute mile.
A Gunter’s surveyor’s chain is exactly 66 feet long, divided into 100 links of 0.66 feet each. An engineer’s chain is exactly 100 feet long, divided into 100 engineer’s links of 1 foot each. The 66-foot chain is used in all PLSS land surveys and historic property descriptions across 30 US states. The 100-foot engineer’s chain is used in civil engineering surveys (road alignment, sewer design, railway stationing) where 100-foot station intervals make design arithmetic convenient. Always confirm which chain type your source document uses before converting. A 40-chain distance is 2,640 ft in a PLSS deed but 4,000 ft in an engineer’s survey.
The National Institute of Standards and Technology (NIST) and NOAA officially deprecated the US Survey Foot on December 31, 2022, through Federal Register document 85 FR 62698. The US Survey Foot was defined as exactly 1200/3937 meters = 0.3048006096… meters, making it approximately 2 parts per million longer than the international foot (exactly 0.3048 m). After January 1, 2023, the international foot is the only foot recognized for new US federal surveying and mapping. The practical impact is small on a single parcel (approximately 0.01 ft per mile), but significant for State Plane coordinate systems over large areas. Historic documents that used US survey feet remain valid in their original form; the change affects new work and software coordinate reference systems.
The correct method: convert each component to the same unit before adding. Using links as the common unit: 42 chains = 4,200 links; plus 15 links = 4,215 links total. Convert to feet: 4,215 x 0.66 = 2,781.9 feet. Alternatively in feet: 42 x 66 = 2,772 ft, plus 15 x 0.66 = 9.9 ft, total 2,781.9 ft. The Legal Description Parser tab in this calculator handles this automatically: paste or type “42 chains 15 links” and click Parse to get the total in feet, chains, and miles.
The PLSS applies to 30 US states. These are primarily states west of the Appalachian Mountains that were federal territory before statehood: Alabama, Alaska, Arizona, Arkansas, California, Colorado, Florida, Idaho, Illinois, Indiana, Iowa, Kansas, Louisiana, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Mexico, North Dakota, Ohio, Oklahoma, Oregon, South Dakota, Utah, Washington, Wisconsin, and Wyoming. The original 13 colonies (plus Texas, Hawaii, and a few others) use metes-and-bounds or other survey systems instead of PLSS. In these PLSS states, virtually all property descriptions for agricultural land, federal land, and large rural parcels use Gunter’s chain measurements. The BLM maintains the PLSS cadastral records.
A link is one hundredth of a Gunter’s chain, equal to exactly 0.66 feet or 7.92 inches (per NIST SP 811). The name comes from the actual metal wire links that made up the original Gunter’s chain surveying instrument: each of the 100 physical metal links was exactly 7.92 inches long. In legal descriptions, partial chain distances are expressed in links rather than decimal chains: “32 chains 47 links” rather than “32.47 chains.” When a description says “47 links,” it means 47 x 0.66 = 31.02 feet.
A rod (also called a pole or perch) is exactly one quarter of a Gunter’s chain, equal to 16.5 feet or 5.0292 meters (NIST SP 811). There are 4 rods in one chain and 25 links in one rod. The rod is a unit that predates Gunter’s chain: it originated in medieval England as the length of an ox-goad (the stick used to prod draft animals). Colonial deeds in the original 13 colonies often express distances in rods. In the PLSS states, rods appear less frequently than chains and links, but some descriptions use all three together.
There are exactly 80 Gunter’s chains in one statute mile. The calculation: 1 mile = 5,280 feet; 1 chain = 66 feet; 5,280 / 66 = 80. This relationship is exact and not approximate. In PLSS surveys, one section of land is exactly 1 mile square, so each side of a section is 80 chains. A quarter section is 40 chains on each side (one half mile). This is why so many deed descriptions read “North 80 chains to the section corner” or “East 40 chains to the quarter section corner.”
There are exactly 10 square chains in one acre. This is the fundamental elegance of the Gunter’s chain system: one chain was designed specifically so that a rectangle 1 chain wide and 10 chains long (or any equivalent arrangement of 10 square chains) would equal exactly one acre. One acre = 43,560 square feet = 10 square chains = 10 x (66 ft)^2 = 10 x 4,356 sq ft = 43,560 sq ft. The acre was originally defined as the amount of land one man could plow in a day with one ox, which was a strip roughly 1 chain wide (66 ft) and 1 furlong long (660 ft = 10 chains), giving 10 square chains or 1 acre.
A vara is a Spanish unit of length that was the standard for land surveys in the territories of New Spain (later Mexico) and their US successor states. In Texas, it is approximately 33.333 inches (2.7778 feet) per the most common US title reference definition. In California, different colonial districts used slightly different vara lengths, ranging from 33 to 33.372 inches. The vara appears in Spanish and Mexican land grant descriptions from the colonial era, which remain legally valid in South Texas, California, New Mexico, and Arizona. When interpreting these descriptions, the specific jurisdiction’s vara definition should be used rather than a generic conversion factor. Modern Texas Property Code recognizes the vara as a legal unit of land measurement.
The primary source for original PLSS survey records, field notes, plats, and cadastral data is the BLM General Land Office Records database (glorecords.blm.gov). This database contains original survey plats and field notes for federal land in all PLSS states, many of which are scanned and searchable online at no charge. For state-owned and privately transferred lands, county recorder offices maintain deed books and plat records. State archive offices hold supplementary survey records. The USGS National Map provides digital PLSS boundary layers for GIS use.
The 2 parts-per-million difference between the US survey foot and international foot is tiny on a single property but accumulates significantly over the scale of a county or region. In State Plane Coordinate Systems, using the wrong foot definition can shift calculated positions by up to 12.9 feet over a million feet of coordinates in some states, as documented by Esri. GIS software, CAD programs, and survey data management systems now need to be configured to use the international foot for all new work. The practical checklist: verify your projection definition says “International Foot” not “US Survey Foot” in your GIS software’s coordinate reference system settings. The National Geodetic Survey (NGS) has updated all NSRS datums and publications to reflect the international foot standard.
Yes, this calculator is appropriate for converting chain-based deed distances to feet or meters for GIS data entry. Use the international foot setting (the default) for all new GIS work as required by NIST since January 2023. For historical document research where the source used US survey feet (pre-2023 State Plane coordinates, USGS survey data from before 2023), use the US Survey Foot toggle to generate the legacy comparison value. The Legal Description Parser tab is particularly useful for rapidly converting metes-and-bounds calls from multiple deeds into consistent feet values for boundary reconstruction in GIS. However, this tool does not compute bearings or close traverses; a professional land surveyor using a COGO (coordinate geometry) program is required for legally defensible boundary work.
A statute mile is a unit of length equal to exactly 5,280 feet = 80 Gunter’s chains. A PLSS section is an area unit: one square mile of land (640 acres). The two terms are related but not identical. The side of one PLSS section equals exactly one statute mile (5,280 feet = 80 chains), and the area of one section equals one square mile (5,280 x 5,280 = 27,878,400 sq ft = 640 acres). However, actual sections on the ground are rarely perfect squares because original surveys accumulated errors over long distances, and boundary lines were adjusted for curvature of the earth at regular intervals (correction lines). Only the easternmost and southernmost tiers of a township are guaranteed to be exactly one mile on a side; all other sections may vary slightly.
The primary NIST sources for US survey unit conversions are: (1) NIST Special Publication 811 (2023 Edition), “NIST Guide for the use of the International System of Units,” which contains the official conversion tables for all US customary units including chain, link, rod, furlong, and acre. (2) NIST node/1582061, “U.S. Survey Foot: Revised Unit Conversion Factors,” which provides the specific table showing exact international foot and US survey foot equivalents for all chain-family units effective January 1, 2023. (3) Federal Register document 85 FR 62698, the official rulemaking for the US Survey Foot deprecation. All three documents are publicly available at no charge from NIST and the Federal Register. The conversion factors in this calculator are derived from these primary sources.
Edmund Gunter chose 66 feet deliberately for mathematical convenience in land measurement. At 66 feet per chain: 10 square chains = one acre (the fundamental agricultural area unit); 80 chains = one mile; 10 chains = one furlong. This means a surveyor using a 66-foot chain can compute areas in acres, distances in miles, and sub-distances in furlongs without any conversion tables or multiplication beyond simple addition. A farm of 40 chains x 40 chains is 1,600 square chains, which is exactly 160 acres (the US Homestead Act quarter-section). Gunter published his design in 1620 in “The Description and Use of the Sector, Cross-Staffe, and other Instruments.” The chain rapidly became the primary land surveying instrument in England and all British colonies, including what became the United States.
Related Surveying and Land Measurement Calculators
All unit conversion factors in this calculator are sourced from NIST Special Publication 811 (2023 Edition) and NIST node/1582061, “U.S. Survey Foot: Revised Unit Conversion Factors,” which reflects the NIST deprecation of the US Survey Foot effective December 31, 2022 (Federal Register 85 FR 62698). The international foot (exactly 0.3048 m) is used as the calculation basis for all results unless the US Survey Foot toggle is selected, which provides legacy values for historical reference only.
The Texas Vara value of approximately 33.333 inches (2.7778 ft) is the most commonly cited US title definition but is not nationally standardized. Users researching Spanish land grant documents should verify the specific vara definition for the jurisdiction and document date. The Legal Description Parser produces approximate results for research purposes; it does not account for bearing errors, closing discrepancies, or original survey monumentation issues.
This tool is for preliminary research and educational use. Results must be verified by a licensed Professional Land Surveyor (PLS) before use in any legal document, boundary determination, or construction project. This site has no affiliation with NIST, BLM, USGS, NGS, or any other government agency. External links are provided for informational reference only.