Mulch Calculator — Bags & Cubic Yards

Quick answer: a 12 × 8 ft bed at 3 in deep needs about 1 cubic yard — roughly 14 bags of 2 cu ft mulch.

Mulch is sold two ways — by the bag at the garden center and by the cubic yard in bulk — and the right unit depends on the size of your beds. This calculator converts bed dimensions and depth into cubic yards, cubic feet and bag counts (1.5, 2 or 3 cu ft), and shows a straight bags-vs-bulk price comparison so you don't pay bag prices for a yard-scale job.

It handles rectangles, circles, triangles and tree rings (donut shape — mulch stays off the trunk), with a settling allowance you control.

How to use it

Measure the bed: length and width (or diameter, base and height) in feet.
Enter the mulch depth — 2–3 in for beds, 4 in for heavy weed suppression. Never pile mulch against trunks.
Set the extra-for-settling percentage (10% is a good default) and your local prices.
Read the result: cubic yards to order (or bag count) and the cheaper of bags vs bulk for your size.

How it works

Volume (ft³) = area × depth ÷ 12. Cubic yards = ft³ ÷ 27. Bags = ft³ ÷ bag size (rounded up). Tree ring area = π × (R_outer² − R_inner²).

Coverage reference: 1 cubic yard covers ~324 ft² at 1 in, 162 ft² at 2 in, 108 ft² at 3 in, 81 ft² at 4 in.
Settling/spill allowance defaults to 10%.
Weight planning range 400–1,200 lb per yd³ depending on material and moisture.
Keep mulch 3–6 in away from trunks — the inner clear circle in tree-ring mode handles this.

Worked example

A 12 × 8 ft bed at 3 in deep: 96 ft² × 0.25 ft = 24 ft³ = 0.89 yd³. With 10% settling: ~0.98 yd³ → order 1 yd³ bulk, or 14 bags of 2 cu ft (26.4 ÷ 2 = 13.2 → 14).

Quick reference

Coverage per cubic yard

Depth	Sq ft covered	2 cu ft bags per 100 ft²
1 in	324	1
2 in	162	2
3 in	108	3
4 in	81	4
6 in	54	6

Bags per cubic yard

Bag size	Bags per yd³
1.5 cu ft	18
2 cu ft	14 (13.5 exact)
3 cu ft	9

FAQ

How many bags of mulch are in a cubic yard?

A cubic yard is 27 ft³: that's 13.5 bags of 2 cu ft, 18 bags of 1.5 cu ft, or 9 bags of 3 cu ft. Buy whole bags, so plan on 14 of the 2 cu ft size.

How deep should mulch be?

2–3 in for most beds, 3–4 in for high weed pressure, and never more than 4 in total around plants — deeper mulch suffocates roots. For a refresh over existing mulch, 1–2 in is enough.

Is bulk mulch cheaper than bags?

Almost always past about 2 cubic yards (≈27 bags of 2 cu ft). Compare on the calculator: bags at $4–6 each vs bulk at $25–55/yd³ plus a delivery fee — bulk wins decisively at yard scale.

How much does a yard of mulch cover?

One cubic yard covers ~108 ft² at 3 in deep, 162 ft² at 2 in, or 81 ft² at 4 in. A typical 12 × 8 ft bed at 3 in needs just under 1 cubic yard.

Why keep mulch away from tree trunks?

Piling mulch against the trunk ("mulch volcanoes") traps moisture against the bark, invites rot and pests, and hides girdling roots. Keep a 3–6 in clear ring around the trunk — the tree-ring mode subtracts it automatically.

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Sources & verification

Data verified: October 11, 2026.

Coverage math: standard landscape formulas (1 yd³ = 27 ft³; coverage = 324 ÷ depth-in-inches).
Depth guidance: university extension recommendations (2–4 in, keep clear of trunks).

Estimates are for planning only — always confirm quantities with your supplier and check local building codes before you buy or build.