Gravel & Mulch Calculator

How to work out gravel and mulch

Landscape material is sold by volume (cubic yards, or bags measured in cubic feet) and, for stone, often by weight (tons). Every estimate starts with the same three numbers: the area you're covering, how deep you want the layer, and what the material weighs.

Step 1: area in square feet

For a rectangle, multiply length by width. A circle is π × diameter² ÷ 4, and a triangle is base × height ÷ 2. If a bed is an odd shape, split it into simple pieces and add them. Use feet: a 12' 6" edge is 12.5 ft.

Step 2: volume

Turn the depth into feet by dividing the inches by 12, then multiply by the area. That gives cubic feet. Divide by 27 to get cubic yards, because a cubic yard is 3 ft × 3 ft × 3 ft = 27 cu ft.

Worked example: a 10 ft × 10 ft area at 3 in deep is 100 × 3 ÷ 12 = 25 cu ft, or 25 ÷ 27 = 0.93 cubic yards.

Step 3: weight in tons

Quarries and landscape yards often sell stone by the ton, so multiply cubic yards by the material's density. Gravel and crushed stone are commonly about 1.4 tons per cubic yard, but the real figure depends on the stone size, the rock type and how wet it is, so ask your supplier for theirs and type it in. At 1.4 t/yd³ the example above is 0.93 × 1.4 ≈ 1.3 tons. Mulch is much lighter and is almost always sold by volume, so use the cubic-yard or bag figure for mulch.

Bags vs bulk

Bagged mulch usually comes in 2 cu ft bags, and some products come in 3 cu ft bags. Divide total cubic feet by the bag size and round up. The 25 cu ft example needs 13 bags of 2 cu ft or 9 bags of 3 cu ft. Once a job gets past a cubic yard or two, bulk delivery is usually less hassle than handling dozens of bags. Compare your supplier's price and delivery fee.

How deep should it be?

Common guidance is 2–4 in for mulch beds (keep mulch pulled back from tree trunks and plant stems), 2–3 in for a decorative gravel path, and deeper, in compacted layers, for driveways. Follow your local supplier's or contractor's advice for anything that has to carry vehicles.

Coverage of one cubic yard

(324 sq ft is 27 cu ft spread 1/12 ft deep; divide by the depth in inches for the others.)

Worked example: a mulch bed

A curved bed is roughly a 24 × 6 ft rectangle plus a half circle 6 ft across. The rectangle is 144 sq ft, and the half circle is π × 6² ÷ 4 ÷ 2 = 14.1 sq ft, for a total of about 158 sq ft. At 3 in deep that's 158 × 3 ÷ 12 = 39.5 cu ft = 1.46 yd³, which is 20 bags of 2 cu ft. Rounding up to 1.5 yards for a bulk order is sensible.

Common mistakes

Related: area calculator for odd-shaped beds, concrete calculator for slabs and footings, and how to measure square footage.