Raised Bed Soil Calculator: How Much Soil to Fill Any Raised Bed
A standard 4×8 raised bed at 12 inches deep holds 32 cubic feet (1.19 cubic yards) of soil mix. At 6-inch depth: 16 cubic feet (0.59 yards). Use this raised bed soil calculator guide formula: Length x Width x Depth (all in feet) = Cubic feet. Divide by 27 for cubic yards. The recommended soil mix for most vegetables is one-third compost, one-third topsoil or garden soil, and one-third coarse perlite or coarse vermiculite for drainage.
Raised beds are one of the best investments a home gardener can make, but they only outperform in-ground beds if they are filled with the right soil at the right depth. Too little depth restricts root growth. Too much of the wrong material (pure compost, for example) collapses into an anaerobic mess after one rainy season. This raised bed soil calculator guide gives you the exact cubic feet and cubic yards for any bed size and depth, plus the soil mix ratios that actually produce vegetables.
The topsoil calculator works for raised bed fill too. Enter your bed dimensions and target depth for cubic yards and bulk vs bagged cost.
Calculate Raised Bed Volume →Raised Bed Soil Volume by Bed Size and Depth
| Bed size | 6-inch depth | 10-inch depth | 12-inch depth | 18-inch depth |
|---|---|---|---|---|
| 2×4 (small) | 4 cu ft / 0.15 yd | 6.7 cu ft / 0.25 yd | 8 cu ft / 0.30 yd | 12 cu ft / 0.44 yd |
| 4×4 (square) | 8 cu ft / 0.30 yd | 13.3 cu ft / 0.49 yd | 16 cu ft / 0.59 yd | 24 cu ft / 0.89 yd |
| 4×8 (standard) | 16 cu ft / 0.59 yd | 26.7 cu ft / 0.99 yd | 32 cu ft / 1.19 yd | 48 cu ft / 1.78 yd |
| 4×12 (long) | 24 cu ft / 0.89 yd | 40 cu ft / 1.48 yd | 48 cu ft / 1.78 yd | 72 cu ft / 2.67 yd |
| 4×16 (long) | 32 cu ft / 1.19 yd | 53.3 cu ft / 1.97 yd | 64 cu ft / 2.37 yd | 96 cu ft / 3.56 yd |
| 8×8 (large) | 32 cu ft / 1.19 yd | 53.3 cu ft / 1.97 yd | 64 cu ft / 2.37 yd | 96 cu ft / 3.56 yd |
This raised bed soil calculator guide formula applies to any rectangular bed. For circular beds: Pi x radius squared x depth = cubic feet (e.g., 3.14 x 2 x 2 x 1 = 12.6 cubic feet for a 4-foot diameter bed at 12 inches). For multiple beds, calculate each separately and sum. Always add 10 to 15 percent for settling during the first growing season, when organic material in the mix compresses and decomposes. For adjacent lawn areas, our topsoil volume guide covers the soil math for lawn areas around the raised beds. For mulch paths between beds, our mulch volume guide has the coverage math.
Soil Mix Ratios That Actually Work
The standard 1/3-1/3-1/3 mix
The most widely recommended raised bed soil mix is: one-third quality compost (for organic matter, nutrients, and biology), one-third topsoil or garden loam (for mineral content and water retention), and one-third coarse perlite or aged wood chips (for drainage and aeration). This formula is widely endorsed by university extension programs and is an adaptation of the Mel Bartholomew Square Foot Gardening mix, updated to avoid the excessive vermiculite cost that made the original formula impractical for most gardeners.
Why pure compost is wrong
Pure compost seems like the obvious raised bed choice, but it fails for two reasons: it compresses dramatically under moisture and its own weight (you can lose 40 percent of bed depth in one season), and it becomes hydrophobic when it dries, causing water to sheet off rather than penetrate. Mix compost with loam and a coarse drainage amendment for a bed that stays productive across seasons without constant rebuilding.
Deep bed mix modification
For beds deeper than 12 inches, it is cost-effective and agronomically sound to fill the bottom 6 to 8 inches with a cheaper bulk material: wood chips, straw, leaves, or a mix of untreated wood material and soil. This “Hugelkultur bottom” decomposes slowly, improves drainage, and reduces the volume of expensive blended soil mix needed. The top 8 to 10 inches is where root growth occurs for most vegetables and should be the full premium mix.
What It Costs to Fill a Raised Bed in 2026
| Method | Cost per cu yd | Total for 4×8 bed | Notes |
|---|---|---|---|
| Bagged garden soil (big-box) | $200 to $350 | $238 to $416 | Most convenient, most expensive |
| Bagged compost + bagged garden soil blend | $120 to $200 | $143 to $238 | Good quality control |
| Bulk blended bed mix delivered | $60 to $120 | $71 to $143 | Best value for 2+ beds |
| Self-mixed (bulk topsoil + compost + perlite) | $45 to $90 | $54 to $107 | Best value, most effort |
How Deep Does a Raised Bed Need to Be?
Minimum depth depends on what you are growing. Shallow-rooted crops (lettuce, herbs, radishes) do well in 6 inches. Most common vegetables (tomatoes, peppers, beans, squash) need 12 inches. Deep root vegetables (carrots, parsnips, beets) perform best in 18 to 24 inches. When in doubt, build 12-inch beds: this depth works for 80 percent of home vegetable varieties and the extra soil volume provides better moisture buffering and temperature insulation than shallower options.
Three Real Raised Bed Soil Projects
Example 1: Two 4×8 beds in Portland, Oregon
A homeowner building two 4×8 beds at 12-inch depth. Total volume: 2 x 32 cu ft = 64 cu ft = 2.37 yards. Self-mixed approach: 0.8 yards bulk compost ($45) + 0.8 yards bulk garden loam ($38) + 15 cubic feet perlite ($65 from garden center) + 0.6 yards wood chip bottom filler ($18). Total: $166 for both beds. She overfilled by 15 percent to account for settling. By mid-summer the beds had settled to approximately 10 inches of productive soil depth, as expected.
Example 2: Six 4×4 beds in Denver, Colorado
A homeowner installing a kitchen garden with six 4×4 beds at 10-inch depth. Total: 6 x 13.3 cu ft = 79.8 cu ft = 2.95 yards. Ordered a custom blend from a local landscape supply: 3 yards of pre-blended raised bed mix at $85/yard delivered. Total: $255 for all six beds. The blend (compost, loam, perlite already mixed) saved three hours of manual mixing. At Denver altitude, the extra drainage from perlite was essential for preventing the waterlogging that Denver clay soils promote.
Example 3: Single deep bed for root vegetables in Chicago, Illinois
A gardener wanting to grow carrots and parsnips built a single 4×8 bed at 18-inch depth. Volume: 48 cu ft = 1.78 yards. Bottom 8 inches: untreated wood chips and aged leaves (essentially free from yard waste). Top 10 inches: premium 1/3 compost, 1/3 loam, 1/3 perlite mix. Top mix needed: 4 x 8 x (10/12) = 26.7 cu ft = 0.99 yards. Cost of top mix: $85 bagged. Total with free filler: $85 for a bed that grew 14-inch Nantes carrots by September. The deep bed cost the same as a standard 12-inch bed in materials but produced dramatically better root crop results.
Enter total bed area and your target depth. The topsoil calculator gives you cubic yards and bulk vs bagged cost comparison.
Calculate Soil Volume →Frequently Asked Questions About Raised Bed Soil
How much soil do I need for a 4×8 raised bed?
A 4×8 raised bed at 12-inch depth needs 32 cubic feet (1.19 cubic yards) of soil mix. At 6 inches: 16 cubic feet (0.59 yards). At 18 inches: 48 cubic feet (1.78 yards). Add 10 to 15 percent for settling during the first growing season. Use the formula: Length x Width x Depth in feet = cubic feet. Divide by 27 for cubic yards.
What is the best soil mix for a raised vegetable bed?
One-third quality compost, one-third topsoil or garden loam, one-third coarse perlite or aged wood chips. This mix provides the nutrient density of compost, the mineral structure of loam, and the drainage of a coarse amendment. Pure compost alone compresses dramatically and becomes hydrophobic when dry. The 1/3-1/3-1/3 mix produces consistent results across most US climates and vegetable varieties.
How many bags of soil do I need for a raised bed?
A 4×8 bed at 12-inch depth needs 32 cubic feet. A typical 40-pound bag of garden soil contains 1 cubic foot. So you need approximately 32 bags for a standard 4×8 bed at 12 inches. Buying in bulk from a landscape supply yard saves significantly: 2 cubic yards of pre-blended bed mix delivered typically costs $120 to $240 versus $320 to $480 for 32 bagged cubic feet.
How deep should a raised bed be for tomatoes?
A minimum of 12 inches for determinate (bush) tomato varieties. Indeterminate (vining) tomatoes that grow 6 to 8 feet tall develop deep root systems and perform significantly better in 18-inch beds. The deeper the bed, the more moisture buffering and temperature stability the roots have, which is particularly important for tomato success in hot or dry climates.
Can I use regular garden soil in a raised bed?
Unamended native soil from your yard is not ideal for raised beds because it typically has poor drainage (clay) or poor water retention (sand), and it compacts under the concentrated moisture and traffic of raised bed use. If you use native soil, amend it heavily with compost (at least 30 percent by volume) and a drainage amendment. Pre-blended raised bed mixes or the 1/3-1/3-1/3 mix are more reliable than native soil for first-time bed builders.
How often should I replace raised bed soil?
Complete soil replacement is rarely necessary. Add 1 to 2 inches of compost to the top of the bed each spring and fall to replenish organic matter and nutrients as the existing compost component decomposes. Every 3 to 5 years, the bed may have settled and compacted enough to warrant adding a full 4 to 6 inch topdress of fresh blended mix. Never till raised bed soil deeply: raised bed success depends on preserving the soil biology and structure that develops over multiple seasons.
What is hugelkultur and should I use it in a raised bed?
Hugelkultur is the practice of filling the bottom of a raised bed with woody material (logs, branches, wood chips) before adding soil mix on top. The wood decomposes slowly, improving drainage and gradually releasing nutrients, while significantly reducing the volume of expensive blended soil mix needed for deep beds. It works well for beds 18 inches or deeper. For standard 12-inch beds, the woody bottom layer takes up too much of the productive root zone; stick with the full premium mix at that depth.
Do raised beds need drainage holes?
Open-bottom raised beds (placed directly on the ground) drain naturally through the soil below. Raised beds on hard surfaces (decks, patios, concrete) need drainage holes in the bottom board or container. Without drainage, even the best soil mix becomes waterlogged and roots rot. For deck and patio beds, use a drill to add holes every 6 to 12 inches across the bottom, then line with landscape fabric to prevent soil loss while allowing drainage.
Related Calculators and Guides
For raised bed soil mix recommendations and vegetable root depth requirements, the Utah State University Extension raised bed gardening guide and your state’s cooperative extension service publish region-specific soil and variety recommendations.