How do I calculate gallons in my pool?

Rectangle: Length x Width x Average Depth x 7.48052. Average depth = (shallow end + deep end) / 2. For a 16x32 pool with 3.5 ft shallow and 6 ft deep: avg = 4.75 ft, volume = 16 x 32 x 4.75 x 7.48052 = 18,231 gallons. Circle: pi x (diameter/2)^2 x depth x 7.48052. Kidney: 0.85 x L x W x avg_depth x 7.48052.

How many gallons is a 16x32 pool?

Depends on depth. With 3.5 ft shallow / 6 ft deep (4.75 ft average): approximately 18,231 gallons. With 4 ft shallow / 7 ft deep (5.5 ft average): approximately 21,091 gallons. Using just the deep end depth (6 ft) overestimates volume by 26%.

🏊 Free US Pool Volume Calculator — 6 Shapes + Chemical Dosing + Pump Sizing

Pool Volume Calculator in Gallons: Rectangle, Circle, Oval, Kidney, L-Shape, and Freeform

Q: How much chlorine do I add per gallon of pool water?

Liquid chlorine 12.5%: 10 oz per 10,000 gallons raises chlorine by 1 ppm. For initial startup to 2 ppm: approximately 1 quart per 10,000 gallons. Pool shock 73% Ca-Hypochlorite: 1 lb per 10,000 gallons. Always calculate based on your pool's actual measured volume.

Q: What pump size do I need for my pool?

APSP minimum: 8-hour turnover. Required GPH = pool gallons / 8. Required GPM = GPH / 60. 15,000 gal = 31 GPM = 0.75-1.0 HP. 20,000 gal = 42 GPM = 1.0-1.5 HP. 30,000 gal = 63 GPM = 1.5-2.0 HP. Use variable-speed pump to reduce energy by 50-80%.

The only US pool volume calculator supporting all 6 common pool shapes with proper shallow-end plus deep-end average depth calculation, plus a complete chemical starter guide (chlorine, shock, stabilizer, algaecide), APSP 8-hour pump turnover GPH and GPM, water weight in pounds and tons, and fill time estimates at standard garden hose flow rates.

🏊 Pool Volume Calculator

Step 1 — Pool Shape

Standard in-ground pool. Formula: L x W x avg_depth x 7.48052

Step 2 — Pool Dimensions

Length (ft)

Width (ft)

Step 3 — Pool Depth

Shallow end (ft)

Deep end (ft)

Average depth = (shallow + deep) / 2. For a 3.5 ft shallow and 6 ft deep: avg = 4.75 ft. This is the correct formula — using only one depth understates volume by 15-30%.

📊 Pool Volume & Estimates

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Select pool shape, enter dimensions and depth — then click Calculate Volume for pool volume in gallons, water weight, chemical dosing estimates, pump GPH, and fill time.

Pool Volume Calculator: Why Using One Depth Number Gives You the Wrong Answer for

Every in-ground pool in the US has a tapered floor — it starts at a shallow end (typically 3 to 4 feet) and slopes down to a deep end (typically 5 to 9 feet). A 16×32 rectangular pool with a 3.5-foot shallow end and a 6-foot deep end has an average depth of 4.75 feet, not 6 feet. If you plug in the deep end depth of 6 feet (as most people do when they can only measure one depth), you calculate 23,040 gallons. The correct volume using average depth is 18,240 gallons — a difference of 4,800 gallons, or 26% more water than the pool actually contains.

This matters enormously when you’re adding chemicals. If your pool actually holds 18,240 gallons and you add shock for 23,040 gallons, you’ve over-shocked your pool by 26% — an expensive mistake that can also temporarily bleach your liner or irritate swimmers’ eyes and skin. The correct calculation is always: average depth = (shallow end + deep end) divided by 2, then multiply by surface area and 7.48052 gallons per cubic foot.

US pool volume formulas by shape: Rectangle: L × W × avg_depth × 7.48052. Circle: π × (diameter/2)² × avg_depth × 7.48052. Oval/Ellipse: (π/4) × L × W × avg_depth × 7.48052. Kidney (NSPI formula): 0.85 × L × W × avg_depth × 7.48052 — the 0.85 factor accounts for the curved indentation. L-Shape: (L1 × W1 + L2 × W2) × avg_depth × 7.48052 — add both rectangle areas. Freeform: measured surface sqft × avg_depth × 7.48052.

US Pool Volume Quick Reference: Common Pool Sizes by Gallons

Pool Type / Size	Surface Sq Ft	Avg Depth (4 ft shallow / 7 ft deep)	Gallons	Water Weight
12 × 24 rectangle (small backyard)	288 sq ft	5.5 ft avg	~11,866	~98,914 lbs
16 × 32 rectangle (standard)	512 sq ft	5.5 ft avg	~21,091	~175,888 lbs
20 × 40 rectangle (large)	800 sq ft	5.5 ft avg	~32,955	~274,814 lbs
18 ft round above-ground	254 sq ft	4 ft (flat)	~7,605	~63,427 lbs
24 ft round above-ground	452 sq ft	4 ft (flat)	~13,530	~112,833 lbs
15 × 30 oval above-ground	353 sq ft	4 ft (flat)	~10,568	~88,137 lbs
20 × 35 kidney (typical HOA)	595 sq ft (×0.85)	5.5 ft avg	~18,512	~154,430 lbs

Three Real US Pool Projects: Volume Calculations and Chemical Estimates

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Example 1: Orlando, FL: 16×32 Rectangle, 4 ft Shallow / 7 ft Deep, Chemical Startup

Orlando, Florida — standard in-ground backyard pool, 16×32 ft, 4 ft shallow, 7 ft deep

An Orlando homeowner just had a new 16×32 in-ground pool installed. The shallow end is 4 feet, the deep end is 7 feet. The pool contractor asks her to add the startup chemicals — but she needs to know the exact volume first.

Calculation	Math	Result
Average depth	(4 + 7) ÷ 2	5.5 ft
Surface area	16 × 32	512 sq ft
Volume (cu ft)	512 × 5.5	2,816 cu ft
Volume (gallons)	2,816 × 7.48052	21,061 gallons
Water weight	21,061 × 8.34052	175,637 lbs (87.8 tons)
Liquid chlorine 12.5% (to reach 2 ppm)	21,061 ÷ 10,000 × 10 oz	21 oz (startup dose)
Pool shock 73% (initial)	21,061 ÷ 10,000 × 1 lb	2.1 lbs
Pump required (8-hr APSP)	21,061 ÷ 8 hrs = 2,633 GPH	44 GPM minimum

✅ Orlando tip: Florida pools require a CYA (cyanuric acid) level of 30-50 ppm to protect chlorine from UV degradation — at 21,061 gallons, you’d need approximately 6 lbs of stabilizer to reach 30 ppm. University of Florida IFAS Extension publishes an excellent Florida Swimming Pool Chemical Management Guide covering Florida-specific requirements. UF IFAS at edis.ifas.ufl.edu has this guide free online. Note that Florida DOH also has specific barrier and safety requirements for residential pools — floridahealth.gov lists county health department contacts for pool inspections.

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Example 2: Dallas, TX: 18 ft Round Above-Ground Pool, 4 ft Depth, Fill Time

Dallas, Texas — 18-foot round above-ground pool, 4 ft depth (flat bottom)

A Dallas family set up their 18-foot round above-ground pool. The pool is 4 feet deep with a flat bottom. They want to know the volume, chemical needs, and how long it will take to fill with their garden hose.

Calculation	Math	Result
Surface area	pi × (18/2)² = pi × 81	254.47 sq ft
Volume	254.47 × 4 ft × 7.48052	7,616 gallons
Water weight	7,616 × 8.34052	63,520 lbs
Fill time @ 9 GPM hose	7,616 ÷ (9 × 60 min)	14.1 hours
Liquid chlorine (to 2 ppm)	7,616 ÷ 10,000 × 10 oz	7.6 oz
Pump needed (8-hr turnover)	7,616 ÷ 8 = 952 GPH	16 GPM — 0.5 HP pump

✅ Dallas tip: Texas summers are brutal on pool chemistry — water temperatures regularly hit 88-92°F, which dramatically accelerates chlorine burn-off and algae growth. Texas A&M AgriLife Extension recommends testing Dallas area pool water every 2-3 days during summer (vs. weekly in other climates) and maintaining chlorine at 3-5 ppm (not just 2 ppm minimum) to account for the higher water temperature. At 7,616 gallons, you’ll need approximately 1 quart of liquid chlorine every 2-3 days in a typical Dallas July. AgriLife Extension at agrilifeextension.tamu.edu has a Texas Residential Pool Maintenance Guide.

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Example 3: Phoenix, AZ: 20×40 L-Shape Pool, 3.5 ft Shallow / 6 ft Deep, Water Truck

Phoenix, Arizona — L-shaped in-ground pool, main section 20×30 + wing 10×15 ft, 3.5 ft shallow / 6 ft deep

A Phoenix homeowner has an L-shaped pool: main section 20×30 ft, plus a smaller wing 10×15 ft. Depth is 3.5 ft at the shallow end and 6 ft at the deep end. Water is being delivered by water truck — how many truckloads?

Calculation	Math	Result
Total surface area	(20×30) + (10×15) = 600 + 150	750 sq ft
Average depth	(3.5 + 6.0) ÷ 2	4.75 ft
Volume	750 × 4.75 × 7.48052	26,659 gallons
Water truck loads	26,659 ÷ 9,000 gal per truck	3 truckloads
Pool shock needed (initial)	26,659 ÷ 10,000 × 1 lb	2.67 lbs shock
Pump (8-hr APSP)	26,659 ÷ 8 = 3,332 GPH	56 GPM — 1.5 HP pump

✅ Phoenix tip: Water delivery by tanker truck is common in Phoenix for initial pool fills due to Arizona’s strict municipal water restrictions during drought conditions. A standard water truck delivers 9,000-10,000 gallons; some operators deliver up to 5,500 gallons per load depending on their truck size. Arizona Department of Environmental Quality (ADEQ) at azdeq.gov has information on Arizona’s water conservation requirements for new pool installations, including the Arizona Swimming Pool Association’s (AZPA) conservation-certified pool guidelines. Phoenix also has specific pool barrier requirements — contact Maricopa County Environmental Services at maricopa.gov.

Three Expert Tips for Accurate Pool Volume and Chemical Management

Always Use Average Depth: Never Just the Deep End or Shallow End Alone

The single biggest volume calculation mistake: using only the deep end depth for the entire pool. A 16×32 pool is NOT 6 feet deep throughout — only the very end of the deep section reaches 6 feet. The floor slopes from 3.5 or 4 feet at the shallow end to the bottom of the deep end. The correct formula is average depth = (shallow end + deep end) ÷ 2. For most standard residential pools: shallow end 3.5 ft, deep end 6 ft → average depth 4.75 ft. Using 6 ft instead of 4.75 ft gives a 26% overestimate of your volume, which means 26% too much chemical added every time you treat your pool. Also note: if your pool has a “hopper” bottom (abrupt step down instead of a gradual slope), the NSPI correction factor changes — use a pool professional’s measurement for hopper-bottom pools.

Your Pump Must Complete One Full Turnover Every 8 Hours: Not Just Move Water

The APSP (Association of Pool and Spa Professionals) minimum standard is that residential pool pump systems must be capable of turning over the entire pool volume in 8 hours. This means if your pool holds 20,000 gallons, your pump must be capable of 2,500 GPH (gallons per hour), which is approximately 42 GPM (gallons per minute). A common mistake is buying a pump that’s rated at 42 GPM at zero resistance, then connecting it with undersized or excessively long plumbing that reduces actual flow to 25-30 GPM. When sizing a pump, account for pipe friction losses: longer pipe runs, smaller pipe diameter, 90-degree elbows, and a dirty filter all reduce actual flow. Use your pool volume from this calculator to verify that your pump and plumbing system can actually achieve the 8-hour turnover standard — not just what the pump label says at peak flow.

Base All Chemical Additions on Your Calculated Volume: Then Test Before Adding More

Pool chemistry is dose-response: the amount of chemical you add depends entirely on your pool’s volume. The chemical estimates in this calculator are for initial fill / startup — a new pool being filled with fresh water. For an established pool that’s already been treated, NEVER add chemicals based on volume alone. Always test first with a reliable 4-way test kit (pH, chlorine, alkalinity, CYA) or a pool store water test, then add chemicals based on the deficit between current and target levels. The proper sequence for chemical additions: alkalinity first (target 80-120 ppm), then pH (7.2-7.6), then calcium hardness (200-400 ppm for plaster pools, 175-225 ppm for vinyl), then chlorine last. Never add two different chemicals to the pool at the same time — add one, wait for full circulation (run pump for 1-2 hours), then retest before adding anything else.

Frequently Asked Questions About Pool Volume in Gallons

How do I calculate the gallons in my pool?+

Rectangle pool: Length × Width × Average Depth × 7.48052. Average depth = (shallow end depth + deep end depth) ÷ 2. Example: 16×32 ft pool, 3.5 ft shallow, 6 ft deep: avg depth = 4.75 ft. Gallons = 16 × 32 × 4.75 × 7.48052 = 18,233 gallons. For a circle pool: π × (diameter/2)² × depth × 7.48052. For oval: (π/4) × length × width × depth × 7.48052. For kidney shape: 0.85 × length × width × depth × 7.48052.

How many gallons are in a 16×32 pool?+

Depends on depth. 16×32 with 3.5 ft shallow / 6 ft deep (avg 4.75 ft): approximately 18,231 gallons. With 4 ft shallow / 7 ft deep (avg 5.5 ft): approximately 21,091 gallons. With a constant 5 ft depth (flat bottom): approximately 19,169 gallons. The difference between using just the deep end depth (6 ft) vs. the correct average (4.75 ft) is about 4,800 gallons — a 26% error that results in significant over-treatment when adding chemicals.

How much does a full pool of water weigh?+

Water weighs exactly 8.34052 lbs per US gallon (at 62°F / 16.7°C standard). A 15,000-gallon pool weighs 125,108 lbs (62.5 tons) of water alone — not counting the concrete shell, coping, decking, or pump equipment. A large 30,000-gallon pool contains 250,216 lbs (125 tons) of water. This water weight is why pool installations require soil bearing capacity assessment in some areas — particularly for rooftop or elevated pools. Most residential in-ground pools are designed to distribute this weight across the pool shell into the surrounding soil.

How many gallons is an 18 ft round above-ground pool?+

18-ft round pool, 4 ft deep: pi × 9² × 4 × 7.48052 = 7,616 gallons. 18-ft round at 4.5 ft deep: 8,568 gallons. 18-ft round at 3.5 ft deep: 6,663 gallons. Above-ground pools typically have a flat bottom (constant depth), so you only need to enter a single depth number — there’s no shallow and deep end like an in-ground pool. If the pool has a slight slope (some oval above-ground pools), use the average of the measured depths.

How much chlorine do I add per gallon of pool water?+

To raise chlorine by 1 ppm in 10,000 gallons: liquid chlorine 12.5% (sodium hypochlorite) = 10 fl oz. Granular chlorine 65%: 2 oz. Chlorine tablets 3-inch (90%): 1 tablet lasts about 5-7 days per 10,000 gallons. For initial startup (new pool at 0 ppm, target 2-3 ppm): liquid chlorine 12.5% = approximately 1 quart per 10,000 gallons. Pool shock (calcium hypochlorite 73%): 1 lb per 10,000 gallons raises free chlorine approximately 7 ppm — use for shock treatment, not routine maintenance. Always calculate based on your pool’s actual volume from this calculator.

How long does it take to fill a pool with a garden hose?+

Standard 5/8-in garden hose at typical US residential pressure (40-50 PSI): 9-17 GPM. At 9 GPM: 10,000 gallons takes 18.5 hours. At 17 GPM: 10,000 gallons takes 9.8 hours. Factors affecting fill time: water pressure at spigot (test with a flow meter), hose length (longer = more friction = lower GPM), hose diameter (3/4 in hose is significantly faster than 5/8 in), and any restrictions from flow control devices or in-line filters. For large pools over 20,000 gallons, water delivery by tanker truck (9,000-10,000 gal per load, fills in 2-3 hours per load) is often faster and avoids stress on residential water meters.

What pump size do I need for my pool?+

The APSP minimum: pump must turn over entire pool volume in 8 hours. Required GPH = pool gallons ÷ 8. Required GPM = GPH ÷ 60. Examples: 15,000 gal = 1,875 GPH = 31 GPM minimum → 0.75-1.0 HP pump. 20,000 gal = 2,500 GPH = 42 GPM → 1.0-1.5 HP. 30,000 gal = 3,750 GPH = 63 GPM → 1.5-2.0 HP. Important: pump HP ratings are at zero resistance — actual flow with plumbing, filter, and fittings is typically 30-40% less. Size your pump based on your plumbing’s actual flow capacity, not just the HP label. Variable-speed pumps (required in many US states since 2021 per DOE efficiency standards) allow you to run at lower speeds for most of the day, reducing energy use by 50-80% vs. single-speed pumps.

How many gallons in a kidney-shaped pool?+

The NSPI (National Spa and Pool Institute, now PHTA) kidney pool formula: 0.85 × length × width × average depth × 7.48052. The 0.85 factor accounts for the curved indentation typical of kidney-shaped pools — it reduces the rectangular bounding box area by 15% to approximate the actual kidney shape. Example: 18×36 ft kidney pool, 4 ft shallow / 7 ft deep (5.5 ft avg): 0.85 × 18 × 36 × 5.5 × 7.48052 = 17,990 gallons. Note that actual kidney pool shapes vary — pools with a deeper indentation (more kidney-like) may need 0.80-0.82, while shallower indentations may be closer to 0.88-0.90. For precise volumes, measure the pool’s actual perimeter and use the freeform calculator mode with your surveyed square footage.

What is pool turnover rate?+

Turnover rate is how many times per day the pump circulates the entire pool volume through the filter. The APSP/ANSI standard for residential pools is a minimum 8-hour turnover (3 complete turnovers per day). Commercial pools often require 6-hour turnover (4 turnovers per day) by state health code. Some water features and pools with heavy bather loads need 4-6 hour turnover. The purpose: filtration removes particles, and sanitizers are only effective when distributed evenly — proper turnover ensures chemical even distribution throughout the pool. If your pool consistently turns green after 24 hours of normal chlorination, insufficient turnover is often the cause before poor chemistry is blamed.

How many gallons of water are in a 24-foot round pool?+

24-ft round pool at 4 ft deep: pi × 12² × 4 × 7.48052 = 13,530 gallons. At 3.5 ft deep: 11,839 gallons. At 4.5 ft deep: 15,221 gallons. 24-ft round pools are common above-ground sizes. Chemical needs at 13,530 gallons: approximately 13.5 oz of liquid chlorine 12.5% per 1 ppm increase. Initial startup shock: approximately 1.35 lbs of 73% calcium hypochlorite. Pump minimum: 13,530 ÷ 8 hrs = 1,691 GPH = 28 GPM — a 0.5 HP to 0.75 HP variable-speed pump is adequate for most 24-ft round pool setups.

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Legal Disclaimer and Editorial Transparency

Pool volume calculations are estimates for planning purposes. Actual pool volume may differ based on construction variations, wall slope, and measurement precision. Chemical dosing estimates are for initial fills of clean water to standard levels — always test current water chemistry before adding any pool chemicals to an established pool. Never add multiple chemicals simultaneously; follow manufacturer directions and local regulations. Pool barrier, fencing, and safety requirements vary by state and county — consult your local building department before construction. Florida requirements: floridahealth.gov. Arizona requirements: azdeq.gov. APSP/PHTA standards at phta.org. USCalculators.com is not affiliated with any pool chemical manufacturer, pool supply company, or pool contractor.