Calculate soil needed for garden beds in cubic feet, cubic yards and number of bags.
The soil volume calculator estimates how many cubic feet (or cubic yards or 1.5-cu-ft bags) of garden soil, raised-bed mix, or topdressing you need for a bed of any rectangular, circular, or trapezoidal shape. Inputs are length, width, and depth — typical USDA-recommended fill depth for vegetable raised beds is 10–12 inches; trees in clay-heavy zones often want 18–24 inches.
Volume = length × width × depth, converted from inches/feet to cubic feet, then to cubic yards (1 yd³ = 27 ft³) and to retail bag count (most US bagged garden soil is 1.5 ft³ per bag, raised-bed mix is 2 ft³). The tool also reports a 10% compaction allowance for freshly delivered bulk soil because peat and compost settle once watered. Numbers assume uniform depth; for trapezoid or sloped beds, treat each section separately.
Length 8 ft, width 4 ft, depth 12 inches → 32 ft³ ≈ 1.2 yd³ ≈ 21 bags of 1.5 ft³ garden soil. Add 10% (about 2 extra bags) for compaction during the first week of watering.
A round 3 ft diameter × 24 inches deep planter holds ≈ 14 ft³ ≈ 9 bags of 1.5 ft³ mix. Tree roots need depth; do not skimp below 18 inches in USDA zones 4–7.
A 100 ft² lawn topdressed with 0.5 inch of compost needs 4.2 ft³ — about 3 bags. This is the typical fall topdressing for established cool-season turf.
No — most amendments are mixed into the total volume. If you stack compost on top as topdressing, calculate that layer separately with depth = compost thickness.
The tool uses the most common bag sizes (1.5 ft³ for garden soil, 2 ft³ for raised-bed mix, 3 ft³ for topsoil). Always check the bag label since regional brands vary.
Loose peat or compost-heavy mixes can lose 8–15% volume after a few good rains. The optional 10% compaction allowance is sized for typical raised-bed mixes; add 15% if your mix is more than 40% compost.