Free tool
Mulch Calculator
Measure the beds, pick a depth, and this works out the cubic yards. Mulch is sold by the cubic yard, so this is the number you order with.
Getting the depth right
- Three inches is the working number. Under 2 inches and weeds come through; over 4 and water struggles to reach the roots.
- Keep mulch back from tree trunks and plant stems. A mound against the bark holds moisture where you do not want it.
- Keep bark and wood mulch at least 1.5 metres away from the house and away from fire pits.
The maths behind it
Length times width gives square feet. Multiply that by the depth in inches, then divide by 324. The answer is cubic yards. One cubic yard covers 324 square feet at 1 inch deep, or 100 square feet at about 3¼ inches deep.
The 324 comes from a cubic yard being 27 cubic feet, and 27 times 12 inches is 324. Nothing else is going on, which is why you can check this calculator against a tape measure and a phone.
Materials this suits
Common questions
How much mulch do I need?
Multiply the length by the width in feet, multiply that by the depth in inches, then divide by 324. A 200 square foot bed at 3 inches deep needs about 1.9 cubic yards.
How much area does a yard of mulch cover?
One cubic yard covers about 160 square feet at 2 inches deep, about 100 square feet at 3 inches deep, and about 80 square feet at 4 inches deep.
How deep should mulch be?
Three inches over bare soil. If the bed already has mulch on it, 1 to 2 inches is usually enough to bring the colour back.
Do I need landscape fabric under mulch?
Usually not. Bark mulch breaks down into the bed over time, which is the point of it, and fabric underneath stops that from reaching the soil. Fabric belongs under decorative rock, which does not break down.