How much mulch or topsoil do I need? Depth, volume and weight
5 min read · Updated 2026-10-12 · BuildCalc
Mulch and topsoil are sold by volume, and both are simple to estimate once you decide the depth. The one that catches people out is topsoil, because soil is heavy: a cubic yard weighs around a tonne, so a job that needs five yards arrives as five tonnes on a truck, and not every driveway can take that.
Area times depth, in consistent units
Measure the bed and multiply by the depth you want, converting the depth from inches to feet. Three hundred square feet at three inches deep is seventy-five cubic feet, or just under three cubic yards. Bulk materials are usually priced by the cubic yard; bags are usually two cubic feet, so dividing the volume by two gives the bag count.
Split irregular beds into rectangles and circles and add them up, since measuring around a curve with a tape rarely gives a reliable figure. A gently sloping bed needs slightly more than the flat measure suggests, because the material settles into the low side.
Choosing the right depth
For mulch, three inches is the standard: deep enough to suppress weeds and hold moisture, shallow enough to let air and water through. Piling mulch up against the trunks of trees and shrubs traps damp against the bark and causes rot, so keep a gap around every stem.
For topsoil, the depth depends on the job. A quarter inch is a dressing to level a lawn, three to six inches levels a new bed, and a raised bed might be filled to ten or twelve inches. Expect topsoil to settle noticeably after the first watering, so allow a little extra rather than filling exactly to the line.
Bulk versus bags, and the weight question
Bulk delivery is much cheaper per cubic foot, but it demands access and a place to tip. Bags cost more per unit and suit small areas, awkward access and top-ups, and they are easier to carry to a bed at the back of a garden. Compare the two on price per cubic foot rather than per bag, and remember delivery charges.
Check the weight before ordering anything large. A cubic yard of topsoil is about a tonne, and gravel is heavier still at around a tonne and a half. If the load has to cross a soft lawn or a paved drive with a weight limit, that decides where it can be tipped — and how far you will be barrowing it.
Run your own numbers
Free calculators that answer the “how much” version of this question. They run entirely in your browser — nothing you type is uploaded or stored.
Common questions
How deep should mulch be?
About three inches for most beds. Thinner loses its weed-suppressing benefit; thicker can mat, shed water and smother roots.
How much does a cubic yard of topsoil weigh?
Roughly a tonne, depending on moisture and composition. Gravel is around one and a half tonnes per cubic yard.
BuildCalc provides general information and planning estimates only, not professional construction, engineering or electrical advice. Material quantities are illustrative and depend on your own project, products and local codes. See our full disclaimer.