How this calculator works
Choose a rectangular bed (length × width) or a round bed (diameter), enter the fill depth and how many identical beds you're filling, and this calculator returns the volume in cubic feet, cubic yards and cubic meters, plus how many bags that takes at your chosen bag size and an estimated weight based on a soil density you can adjust.
Bagged garden soil commonly comes in 0.75, 1, 1.5 and 2 cubic foot bags, so buying the right size (or combination) matters for cost — bulk soil delivered by the cubic yard is usually far cheaper for large beds. Soil density varies substantially with moisture content and composition; the default of about 1.3 tons per cubic yard is a typical figure for moist bagged topsoil, but dry, sandy, or compost-heavy soil can weigh meaningfully more or less. Enter your supplier's actual density if you know it — the weight estimate is only as good as that number.
The formula
Rectangular bed volume = length × width × depth (depth converted to feet: inches ÷ 12)Round bed volume = π × (diameter ÷ 2)² × depth; total volume = volume per bed × number of bedsCubic yards = cubic feet ÷ 27 exactly; weight (tons) = cubic yards × density (tons per cubic yard)1 cubic yard = 27 cubic feet exactly, and 1 cubic foot = 0.3048³ cubic meters exactly, following the international foot definition — both conversions used here are exact, not approximations.
Worked example: a 4 ft × 8 ft raised bed, 12 in deep
- Depth in feet: 12 ÷ 12 = 1 ft.
- Volume: 4 × 8 × 1 = 32 cubic feet, for 1 bed.
- In cubic yards: 32 ÷ 27 ≈ 1.185 cubic yards. In 1.5 cu ft bags: 32 ÷ 1.5 ≈ 21.3, rounded up to 22 bags.
- Estimated weight at 1.3 tons/yd³ (typical moist topsoil): 1.185 × 1.3 ≈ 1.54 tons.
Frequently asked questions
How deep should I fill a raised garden bed?
8 to 12 inches is typical for most vegetables and annuals, since it gives roots enough depth without needing an excessive volume of soil; root crops and some perennials benefit from 12 inches or more. Shallower beds (6 inches) can work for herbs and shallow-rooted plants.
Why does the weight estimate vary so much?
Soil bulk density changes with moisture — wet soil is noticeably heavier than dry soil of the same volume — and with composition, since sand, clay, compost and topsoil all pack differently. The 1.3 tons per cubic yard default is a reasonable planning figure for moist topsoil, but enter your specific product's listed density for a more accurate weight, especially if you're checking a delivery vehicle's load limit.
Is garden soil the same as topsoil, potting mix, or compost?
No — they're different products with different densities and compositions. Topsoil is mineral soil from the uppermost ground layer, potting mix is a lighter, often soilless blend designed for containers, and compost is fully decomposed organic matter; this calculator's volume math applies to any of them, but the default density assumes topsoil specifically.
How do I calculate an irregularly shaped bed?
Break it into rectangular or round sections, calculate each section's volume separately using this calculator (with the bed count set to 1 for each unique shape), and add the resulting cubic feet together for your total order.
How many 2 cubic foot bags would the 4 by 8 foot example bed need instead of 1.5 cubic foot bags?
16 bags. The example bed (4 by 8 feet, filled 12 inches deep) needs 32 cubic feet of soil total regardless of bag size; dividing 32 by a 2 cubic foot bag gives exactly 16 bags, compared with the 22 bags used in the 1.5 cubic foot version of the same example. The total soil volume stays identical either way — a larger bag size just means fewer, heavier bags to buy and carry.