Coverage depends on the depth you spread.
Coverage = available bag volume ÷ depth ÷ loose-volume multiplier ÷ (1 + waste ÷ 100)
Start with the label, then choose depth
Multiply the labelled volume of one bag by the whole number of bags you have. Divide by the intended layer depth to find the area. A bag does not have a fixed coverage area without a depth. This reverse tool accepts cubic feet, cubic yards, litres or cubic metres.
Allowances reduce coverage
If you reserve a waste buffer or need a loose-volume adjustment, less of the available volume covers the target layer. Coverage equals available volume ÷ depth ÷ multiplier ÷ (1 + waste/100). Keep the adjustment at 1 and waste at zero unless you have a reason to change them.
A worked coverage example
Five 2 ft³ bags contain 10 ft³. Spread at 3 in (0.25 ft) deep, they cover 40 ft² with no allowances. At 6 in they cover 20 ft². Reserving a 10% ordering buffer at 3 in reduces planned coverage to about 36.36 ft².
Plan from stock, then check the footprint
This reverse tool tells you how much area your available bags can cover at a chosen depth. Measure the intended footprint separately. If it exceeds the displayed coverage, use the relevant material calculator to find the total bags required rather than rounding the coverage upwards.
A depth comparison you can verify
Six 50-litre bags contain 300 litres, or 0.3 m³. With no adjustments, they cover 6 m² at 5 cm deep, 3 m² at 10 cm or 12 m² at 2.5 cm. These are arithmetic comparisons, not recommendations for spreading a material at those depths.
Keep a reserve separate from usable coverage
A 10% buffer is applied as a factor in the denominator: the planned area is available volume divided by depth and 1.1. It is not the same as subtracting 10% of the displayed area. Keep the convention consistent when comparing this reverse calculation with a forward material estimate.
Before you place an order
Check dimensions, bag yield and the price basis. Whole bags round up; bulk orders may have minimum quantities or delivery charges that this calculator does not include. All adjustments are your inputs. Read our method, unit definitions and limits.
Useful questions
My bag says 25 kg. Can I use it here?
This reverse tool needs volume. Ask the supplier for the volume or use a material calculator with a suitable loose bulk density and a mass-based bag.
How do I find bags for a known garden area?
Use the relevant material calculator. It calculates the volume first, then rounds the required number of bags up.