Mulch Coverage Calculator

Mulch is sold by volume but spread by area, which is where most orders go wrong. Enter the length and width of each bed along with the depth you want, and the calculator returns the volume you need — in cubic yards for bulk delivery and in bags if you are buying by the sack.

How deep should mulch be?

Two to three inches is right for most beds. That is enough to block light from weed seeds and slow evaporation from the soil, without being so deep that light rain never reaches the roots underneath. Under an inch does very little; much over four and you start to suffocate the soil and encourage roots to grow up into the mulch layer rather than down.

Keep it off the stems. Mulch piled against a trunk or the crown of a shrub holds moisture where the plant least wants it and invites rot — leave a couple of inches clear all the way round.

Bags or bulk?

A cubic yard is 27 cubic feet, and bagged mulch usually comes in two or three cubic foot bags, so a yard is somewhere between nine and thirteen bags. Past about three yards, bulk delivery is normally cheaper and far less work than stacking and splitting bags — the trade-off is that it arrives as a pile on the drive and has to be moved the same day.

When to top it up

Organic mulches break down into the soil, which is the point of them, so beds settle by an inch or so a year. Rather than adding a fresh layer over the old one every spring, rake what is there to loosen any crust and measure what is left first — often you only need to top up the thin spots. Once the total depth creeps past four inches, strip some out before you add more.

Shredded leaves make a good free mulch if you have trees, and running them over with the mower first is what makes them usable. Our guides to what mulching on a mower actually does and the right mower height for mulching leaves cover the technique.