How to calculate mulch
Mulch is sold by volume: bags are labelled in cubic feet and bulk mulch is sold by the cubic yard (27 cu ft). Multiply the bed area in square feet by the depth in inches, divide by 12 for cubic feet, then divide by the bag size — or by 27 for yards.
Worked example — 100 sq ft at 3 in: 100 × 3 ÷ 12 = 25 cu ft. That is 13 bags of 2 cu ft (25 ÷ 2 = 12.5, rounded up), 17 bags of 1.5 cu ft, or 0.93 cubic yards in bulk.
Bags per yard and coverage per bag
| Bag size | Bags per cubic yard | Covers at 2 in | Covers at 3 in |
|---|---|---|---|
| 1.5 cu ft | 18 | 9 sq ft | 6 sq ft |
| 2 cu ft | 13.5 | 12 sq ft | 8 sq ft |
| 3 cu ft | 9 | 18 sq ft | 12 sq ft |
| 1 cubic yard (bulk) | — | 162 sq ft | 108 sq ft |
Read the label before you load the cart: the same brand can come in 1.5 and 2 cu ft bags (Scotts Nature Scapes is sold in both), and the bag count changes by a third.
How deep should mulch be?
| Mulch | Depth (MSU Extension) |
|---|---|
| Dyed mulch (black, brown, red) | 2–4 in |
| Shredded hardwood | 2–4 in |
| Pine bark nuggets / mini nuggets | 2–3 in |
| Cypress mulch | 2–3 in |
| Compost (as mulch) | 2–3 in |
| Rubber mulch | 2–4 in |
| Pine straw (bales) | 6–8 in |
Three inches is the sweet spot for most bark and shredded wood: thick enough to block weed seedlings, thin enough for water to reach the soil. Pine straw goes down 6–8 in loose because it settles; a bale covers about 40 sq ft.
Tree rings without the volcano
Mulch a flat ring 3–6 ft out from the trunk (MSU Extension), 2–3 in deep, and keep it 2–3 in back from the bark (City of Rockville, 2026). A 6 ft ring around a 6 in trunk with a 3 in gap is 27.5 sq ft — about 7 cu ft at 3 in, or four 2 cu ft bags. See 6 ft, 8 ft and 10 ft rings.
Topping up existing mulch
Organic mulch breaks down, so beds lose depth every year. Measure what is left with a ruler and add only the difference: bringing 200 sq ft from 2 in to 3 in takes 1 in — 16.7 cu ft, or 9 bags — not the 25 bags of a fresh 3 in layer. Avoid building past 3–4 in in total. MSU Extension suggests raking off the old layer and starting fresh after about three years.
Bags or bulk?
At Mulch Pros' October 2026 prices a 2 cu ft bag of dyed mulch is $3.65 — $49.28 per cubic yard — while bulk is $33.95 a yard. With their $60 minimum delivery fee, bulk wins from about 3.9 cubic yards (roughly 420 sq ft at 3 in); at a $75 fee it is about 4.9 yards. If you can pick it up yourself, bulk is cheaper at any size. LawnStarter puts bulk mulch at $30–$135 a yard nationally with delivery at $70–$140. Watch big-box pallet deals: their pallet price includes delivery, so each bag costs more than the shelf price.
Playground mulch is a different job
Landscape depths are far too thin for fall protection. The CPSC asks for at least 9 in of wood chips or wood mulch, maintained — start with 12 in because loose fill compresses — and the surfacing must extend 6 ft past the equipment on every side. A 10×12 ft swing set therefore needs 22×24 ft of surfacing: about 19.6 cubic yards. Shredded rubber is the exception at 6 in. See the 10×12 swing set answer.
Common mistakes
- Buying by the number of bags a neighbor used without checking the bag size.
- Re-mulching to full depth every spring instead of topping up the difference.
- Piling mulch against tree trunks and house siding.
- Using garden depths (2–3 in) under play equipment, where CPSC asks for 9–12 in.
- Forgetting that a full yard of wet mulch weighs far more than the 400–800 lb of a dry one.
Starting a new bed? Work in compost or topsoil first with the topsoil calculator. Gravel or river rock instead of mulch? Use the gravel calculator. Common sizes: 100 sq ft, 200 sq ft, 500 sq ft, 1,000 sq ft.