Mulch Calculator — cubic yards and bags

How it works

Mulch for a garden bed is worked out by volume, then converted to the number of bags you need to buy:

cubic yards = (length × width × depth) ÷ 27

with dimensions in feet (depth is entered in inches and converted, ÷12). Dividing by 27 gives cubic yards, since one cubic yard is 27 cubic feet.

For bags, divide the volume in cubic feet by the bag size and round up:

bags = ⌈cubic feet ÷ bag size⌉

Bagged mulch usually comes in 2-cubic-foot bags, but 1.5 and 3 ft³ are also sold, so the bag size is an input. Bulk mulch by the cubic yard is cheaper for large beds — one cubic yard replaces about 13–14 of the 2 ft³ bags.

Worked example

A 20 × 10 ft bed mulched 3 inches deep is 20 × 10 × 0.25 = 50 cubic feet = 1.85 cubic yards. At 2 ft³ per bag that is 50 ÷ 2 = 25 bags. A 40 × 20 ft area 2 inches deep is about 133 cubic feet, which is 67 bags — the point where bulk delivery makes more sense.

Frequently asked questions

How much mulch do I need?

Multiply length × width × depth (in feet) and divide by 27 for cubic yards; if the depth is in inches, divide it by 12 first. For bags, divide the cubic-foot volume by your bag size (usually 2 ft³) and round up.

How many bags of mulch are in a cubic yard?

At 2 cubic feet per bag, one cubic yard (27 cubic feet) is about 13.5 bags — so 14 bags in practice. Larger 3 ft³ bags give 9 per yard. Bulk mulch by the yard is usually cheaper than bags for anything above a yard or two.

How deep should mulch be?

Two to three inches is typical for garden beds — enough to suppress weeds and hold moisture without smothering roots. Around trees, keep mulch a few inches back from the trunk and no more than about 3 inches deep to avoid rot.

How much extra mulch should I get?

A little extra is fine, but mulch does not compact like gravel, so you need less buffer — round the bag count up (this calculator already does) and maybe add one bag. For bulk, round up to the nearest quarter yard.

Should I buy mulch in bags or in bulk?

Bags are convenient for small beds and easy to carry; bulk (by the cubic yard) is cheaper per unit and better for large areas, but needs a truck or trailer and a place to dump it. The crossover is usually around one to two cubic yards.

How is the mulch calculation different from gravel?

The volume math is the same — area times depth. Mulch is sold in bags, so this page divides the volume by the bag size; gravel is sold by weight, so the gravel calculator multiplies by a density to give tons instead.