Mulch Calculator
Measure the bed, choose a depth, and get the mulch in cubic yards and cubic feet, the number of 2 ft³ and 3 ft³ bags to buy, and a bulk-versus-bagged cost comparison. Depth guidance follows university extension advice: two to four inches, never piled against a trunk.
Mulch needed
2.04 yd³
28 × 2 ft³ bags · 200 ft² at 3.0 in
| Cubic yards | 2.04 yd³ |
| Cubic feet | 55.00 ft³ |
| Cubic metres | 1.56 m³ |
| 2 ft³ bags (rounded up) | 28 |
| Bagged cost | — |
| Bulk cost | — |
Rounding: bag counts round up; volumes include the settling allowance. Keep mulch a few inches clear of trunks and stems — never pile it into a cone.
Depth is the decision that matters
Mulch volume is simple geometry — area times depth — but the depth is where most jobs go wrong, and it goes wrong in one direction. Extension services recommend a layer of two to four inches; garden beds and tree rings across the country are routinely buried under twice that, often heaped against the trunk.
Too deep is not just wasted money. A thick layer mats into a crust that sheds water, starves roots of oxygen and keeps bark permanently damp. This calculator works to the recommended range, warns you when the depth leaves it, and turns the volume into the bags or bulk yards you actually buy.
How to use the mulch calculator
- Pick the shape. A rectangular bed, a circular tree ring, or an area you have already measured. Odd-shaped beds split into rectangles; run each one and add them up.
- Measure the area. Length and width of the bed, or the diameter of the ring around each tree. Ideally a tree ring reaches out towards the drip line of the canopy.
- Choose the depth. Two to four inches is the range extension services recommend: two to three for fine, composted mulch and three to four for coarse chips and bark.
- Allow for settling. Fresh mulch is fluffy and settles as it breaks down. Ten per cent is a reasonable default; the calculator adds it to the volume.
- Choose bags or bulk. Pick your bag size and, if you know them, the bag and bulk prices. The result compares the two so you can see where a delivered load starts to pay.
- Spread it right. Keep mulch a few inches clear of trunks and plant stems, and spread it flat. A cone of mulch against a trunk — the "mulch volcano" — causes rot and invites pests.
Key formulas
- Bed area: length × width; tree ring: π × diameter² ÷ 4 per tree
- Volume: V (ft³) = area × (depth in inches ÷ 12) × (1 + settling%)
- Cubic yards: yd³ = ft³ ÷ 27
- Bags: ⌈ft³ ÷ bag size⌉ — 2 ft³ or 3 ft³ in the US, 50 L or 75 L in metric markets
Worked example
A 20 × 10 ft border at 3 inches with a 10% settling allowance: 200 × 0.25 = 50 ft³; with allowance 55 ft³ = 2.04 yd³. In 2 ft³ bags that is 55 ÷ 2 = 27.5, rounded up to 28 bags — or a little over two yards delivered loose.
Depth and coverage guide
| Material or use | Depth | Note |
|---|---|---|
| Compost, fine mulch | 2–3 in (5–7.5 cm) | Breaks down quickly; top up each season |
| Shredded bark, wood chips | 3–4 in (7.5–10 cm) | Coarse texture stays open and lasts longer |
| Tree rings | 2–4 in (5–10 cm) | Keep a few inches clear of the trunk |
| Pathways | 3–4 in (7.5–10 cm) | Coarse chips over landscape fabric |
| Depth | Area per cubic yard | 2 ft³ bags per yard |
|---|---|---|
| 2 in | 162 ft² | 13.5 |
| 3 in | 108 ft² | 13.5 |
| 4 in | 81 ft² | 13.5 |
Depth guidance follows university extension advice (for example the Illinois, Vermont and Nebraska extension services), which consistently put the range at two to four inches.
Things to keep in mind
- No mulch volcanoes. Mulch heaped against a trunk keeps the bark wet, invites rot and rodents, and can encourage roots that girdle the tree.
- Weed first. Mulch suppresses new weeds; it does not reliably kill established ones. Clear perennial weeds before spreading.
- Fresh chips and nitrogen. Fresh wood chips can tie up nitrogen at the soil surface as they break down; keep them on top of the soil rather than digging them in.
- Bulk means a pile. A delivered load is tipped in one place — plan where it lands and how it gets to the beds before ordering.
Frequently asked questions
How deep should mulch be?
Two to four inches. University extension services are consistent on this: fine, composted mulch at two to three inches and coarse wood chips or bark at three to four. Thinner than two inches does little to stop weeds or hold moisture; deeper than four starts to mat down and starve roots of oxygen.
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet, so it takes 13½ bags of 2 ft³ or 9 bags of 3 ft³. That is why bulk delivery quickly becomes the cheaper option on larger beds — check the bulk price per yard against the bag price before buying more than a couple of yards in bags.
How much area does a yard of mulch cover?
At 3 inches deep, one cubic yard covers about 108 ft². At 2 inches it covers about 162 ft², and at 4 inches about 81 ft². The general rule is 324 ÷ depth in inches = square feet per cubic yard.
Should mulch touch the tree trunk?
No. Pull it back a few inches from the trunk so the root flare stays visible. Mulch piled against the bark holds moisture against it, encourages rot and gives rodents cover to chew the trunk. Spread it as a flat ring — a donut, not a volcano.
Should I remove old mulch before adding new?
Not usually. Rake the old layer to break up any matted crust, then top it up so the total depth stays within two to four inches. Adding a fresh four inches every year on top of last year’s is how beds end up buried under a foot of mulch.
Why add a settling allowance?
Mulch is delivered loose and settles as it is watered and begins to decompose, so a bed spread at exactly three inches will sit lower within weeks. A ten per cent allowance keeps the settled layer close to the depth you planned without overdoing it.
Last updated: 25 October 2026