How Much Mulch, Topsoil, or Gravel Do I Need?

Mulch, topsoil, compost, and gravel are all the same arithmetic. Get one number in your head and you can estimate any of them: one cubic yard covers 324 square feet at one inch deep.

That comes straight from the units — a cubic yard is 27 cubic feet, and 27 × 12 inches per foot = 324. So coverage at any depth is 324 divided by the depth in inches. At 3 inches, one yard covers 108 square feet.

The formula

Cubic yards = area in sq ft × depth in inches ÷ 324

A 400 sq ft bed at 3 inches: 400 × 3 ÷ 324 = 3.7 cubic yards. In BeaverPlot the Ground Cover calculator does this, and adds the two things the formula alone won't tell you: how many bags that is, and for gravel, roughly how many tons.

What depth should you actually use?

• Mulch — 2 to 3 inches. Enough to suppress weeds and hold moisture. Deeper starts to smother roots, and piling it against a trunk invites rot.
• Topsoil — about 2 inches for levelling or prepping before sod. Building a new bed from scratch is a different job and wants more.
• Gravel — 3 inches for a path or a decorative bed; more for a driveway, which also wants a compacted base underneath.

Bags or bulk?

Bagged mulch and soil are usually 2 cubic feet each, so a cubic yard is about 13 and a half bags. That maths turns nasty fast: our 3.7-yard bed above is roughly 50 bags. Past about three cubic yards, bulk delivery is almost always cheaper and far less lifting.

Getting the area without a tape measure

The formula needs an area, and pacing out an irregular bed is where the error creeps in. Measure it on the map instead: Tools ▸ Measure a Site, trace the bed, save it, then open Ground Cover and tap Use a saved site. The area carries across, so there's nothing to retype and nothing to mistype.

Site measurement and all the calculators are free, and none of it needs a LiDAR phone.

Get BeaverPlot, or start with measuring your lawn from your phone.