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Mulch Calculator
Enter the bed area and the depth you want to see the volume and the bags to buy.
The formula
cubic feet = area × depth ÷ 12
cubic yards = cubic feet ÷ 27
bags = ⌈ cubic feet ÷ bag size ⌉
Worked example
A 200 ft² bed at 3 in deep, in 2 ft³ bags
- 200 × 3 ÷ 12 = 50 ft³
- 50 ÷ 27 = 1.85 yd³
- 50 ÷ 2 = 25 bags
Where this goes wrong
Working in inches of depth and cubic feet of volume at once
Depth is the only measurement here in inches, and forgetting to divide it by twelve multiplies the answer by twelve. A 200 ft² bed at 3 in deep needs 50 ft³ of mulch — not 600, which is twenty-two cubic yards and a lorry you did not want.
Questions
- How deep should mulch be?
- Two to three inches is the range usually recommended — deep enough to suppress weeds, shallow enough to let water and air through. Growers also warn against piling it against stems and trunks, where it holds damp against the plant. Both are widely repeated guidance rather than a figure this page can attribute to a source, so treat them as a starting point.
- When is loose mulch cheaper than bags?
- A cubic yard is 27 cubic feet, so it takes around 13 or 14 of the common 2 ft³ bags. Once you are carrying that many, the delivered price of loose material is usually lower and the handling is certainly easier.
- Does this work for gravel and topsoil too?
- The volume does — area times depth is the same arithmetic whatever fills it. The weight does not, because it depends on the material density, which is why no weight is shown here.