Compost Calculator
Compost in cubic yards and bags from the bed size and depth
Why a range and not one number: compost is quoted at about 500 lb per cubic yard, but the real figure runs from 300 to 1,000 lb. Dry compost is only 300-700 lb per cubic yard. It is mostly air and organic matter, so it is the lightest material here — and the one that gains the most weight after rain. Order against the cubic yards — suppliers convert to tons using their own material’s density, and that is the number that should win.
The calculation
cubic yards = (length x width x depth in inches / 12) / 27
The two conversions in that line are where the mistakes happen. Depth is quoted in inches while the area is in feet, so it must be divided by 12 first; and a cubic yard is 27 cubic feet, not 3, because it is 3 ft in each of three directions.
How deep should it go?
| Use | Typical depth |
|---|---|
| Topdressing a lawn | ¼-½ in, raked in |
| Amending a new bed | 2-3 in, dug into the top 6-8 in of soil |
| Mulching around plants | 1-2 in, kept off the stems |
| Filling a raised bed | blend, usually about a third compost to two thirds soil |
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Frequently Asked Questions
How do I work out how much compost I need?
Multiply the area by the depth, then convert to cubic yards. A bed 20 ft by 10 ft at 3 in deep is 200 sq ft x 0.25 ft = 50 cubic feet, and 50 / 27 = 1.85 cubic yards. Depth is the input people get wrong, because it is given in inches while everything else is in feet.
How many tons is a cubic yard of compost?
About 0.25 US tons, using a typical density of 500 lb per cubic yard. The honest range is 0.15 to 0.50 tons. Dry compost is only 300-700 lb per cubic yard. It is mostly air and organic matter, so it is the lightest material here — and the one that gains the most weight after rain.
Should I order by cubic yards or by tons?
By cubic yards wherever you can. Volume is fixed by your measurements, while tonnage depends on the density of the specific material on the day — including how wet it is. If a supplier quotes tons, let them do the conversion from your yardage using their own density.
Should I add extra for settling?
Usually yes. Loose material compacts once it is spread and walked on, and every job loses a little to spillage and uneven subgrade. Ordering 5 to 10 percent over the calculated volume is normal; running short mid-job costs a second delivery charge.