How do I calculate how much mulch I need?

Multiply the bed area by the depth, in the same units, to get the volume.

How deep should mulch be?

About 5–7.5 cm (2–3 inches) for most beds, up to 10 cm to suppress weeds.

How much does a cubic yard of mulch cover?

Roughly 100 square feet at 3 inches deep.

How Much Mulch Do I Need?

Published 10/9/2025 · 3 min read · Everyday calculators

Marco Bianchi — Home, DIY & motoring writer at Allin

Renovation · Materials

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In short

To find how much mulch you need, multiply the bed's area by the depth you want, in the same units. A 10 m² bed at 7.5 cm (0.075 m) deep needs 10 × 0.075 = 0.75 cubic metres. In imperial, area in square feet × depth in feet ÷ 27 gives cubic yards. Mulch is usually sold by the bag (litres) or in bulk (cubic metres or yards).

Wood chippings spread over the ground, close up. — Mike Bird · Pexels · Pexels

Multiply the bed's area by the depth you want. Here's the volume formula, how deep to spread it, bags vs bulk, and the cubic-yard version.

The volume formula

Mulch is spread as a layer, so the amount you need is a volume: area times depth. The trick is to keep the units the same. Measure the bed in square metres, put the depth in metres too, and multiply. A 10 m² bed at a 7.5 cm layer is 10 × 0.075 = 0.75 cubic metres. If your bed is an odd shape, split it into rectangles, work out each area, add them up, then apply the depth once to the total.

How deep to go

Depth depends on the job. A 5 cm layer refreshes an established bed and keeps it tidy; 7.5 cm is a good general depth; up to 10 cm suppresses weeds well on a new bed. Resist going deeper than that, especially around plant stems and tree trunks — piling mulch against them traps moisture and can rot the base. Keep it a few centimetres clear of stems, and top up thinly each season rather than burying the bed.

Bags vs bulk

Small jobs are easiest with bags, which are sold by volume in litres — a 50-litre bag is 0.05 m³, so it covers roughly two-thirds of a square metre at 7.5 cm deep. For a big garden, buying in bulk by the cubic metre or cubic yard is far cheaper per unit and saves hauling dozens of bags. Work out your total volume first, then decide: a few square metres means bags, a whole border means bulk.

Cubic yards (imperial)

In places that buy mulch by the cubic yard, the maths is the same idea in different units. Take the area in square feet, multiply by the depth in feet (so 3 inches is 0.25 ft), then divide by 27 to turn cubic feet into cubic yards. As a handy benchmark, one cubic yard of mulch covers about 100 square feet at 3 inches deep — a useful figure to sanity-check any estimate before you order a truckload.

Worked with our own calculator

Mulch calculator

Given

Area (m²): 20
Depth (cm): 5

Result

Volume (m³): 1
50 L bags: 20

These figures are produced by the calculator below, not typed in by hand — they are recomputed whenever the tool changes.

Run it on your own figures →

Frequently asked questions

How do I calculate how much mulch I need?: Multiply the bed area by the depth, in the same units, to get the volume.
How deep should mulch be?: About 5–7.5 cm (2–3 inches) for most beds, up to 10 cm to suppress weeds.
How much does a cubic yard of mulch cover?: Roughly 100 square feet at 3 inches deep.

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Sources

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