Raised Bed Soil Calculator
Work out exactly how much soil to buy for a raised garden bed — cubic feet, cubic yards and the number of bags for any bed size.
How it works
Cubic feet = length(ft) × width(ft) × depth(ft) · depth(ft) = depth(in) ÷ 12 · Cubic yards = ft³ ÷ 27 · Bags = ⌈ft³ ÷ bag size⌉
Soil volume is just the box the bed encloses: length × width × fill depth, with the depth converted from inches to feet by dividing by 12. Bulk soil is sold by the cubic yard (27 ft³), while bagged mixes are sold in cubic feet, so both are shown. A common approach is to fill the lower portion of a deep bed with cheaper material and reserve premium mix for the top 8–12 inches where roots grow.
Worked example
An 8 ft × 4 ft bed filled 10 inches deep: 8 × 4 × (10 ÷ 12) = 26.7 ft³, or 0.99 yd³. At 1.5 ft³ per bag that is ⌈26.7 ÷ 1.5⌉ = 18 bags.
Frequently asked questions
How deep should a raised bed be?
Most vegetables root well in 8–12 inches of soil. Root crops like carrots and deep feeders like tomatoes appreciate 12 inches or more, while lettuce and herbs are happy in 6–8 inches.
Should I buy bulk or bagged soil?
Bulk soil by the cubic yard is far cheaper per volume once you need more than about 10–12 bags, but bagged mix is easier to handle and store. This calculator gives both so you can compare.
Can I fill the bottom with something cheaper?
Yes. For beds deeper than a foot, many gardeners fill the bottom with logs, leaves or coarse compost (a "hugelkultur" or lasagna approach) and top with quality soil, which cuts cost and improves drainage.
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This calculator is for educational purposes. Double-check important results before acting on them.