Buying mulch is a guessing game when the store sells 2 cubic foot bags and the landscape yard sells by the cubic yard. This mulch calculator tells you exactly how much to buy in either form. Enter the length, width and depth of your bed — or the diameter of a tree ring — and it returns cubic yards, the number of 2, 3 and 1.5 cubic foot bags, and an optional cost so you can compare bagged against bulk.
The default depth is 3 inches. Clemson University's Home & Garden Information Center notes that fine-textured wood and bark mulches should be no more than 2 to 3 inches deep, because thicker layers can starve roots of air. If you are building a new bed, first work out the soil with the topsoil calculator; for decorative stone instead of mulch, use the gravel calculator.
How to use the mulch calculator
- Measure each bed. Choose Rectangle for straight beds or Circle for rings around trees.
- Enter the depth you want. Use 2–3 inches for most wood and bark mulch; top up an existing layer with 1 inch.
- Keep a small waste allowance (5%) for settling and uneven edges.
- Read the cubic yards for bulk delivery, or the bag counts for store-bought mulch. Bags are always rounded up.
- Enter a bulk price per yard and a price per bag to see which is cheaper for your project.
Formula
For a tree ring, the area is π × (diameter ÷ 2)². To mulch around a tree without touching the trunk, measure the outer ring diameter; the small gap at the trunk barely changes the total.
Worked example
A front bed is 20 ft long and 5 ft deep, mulched 3 inches thick.
- Area: 20 × 5 = 100 ft².
- Volume: 100 × 3 ÷ 12 = 25 ft³.
- With 5% extra: 25 × 1.05 = 26.25 ft³ = 0.97 yd³.
- Bags: 26.25 ÷ 2 = 13.1 → 14 bags of 2 ft³, or 26.25 ÷ 3 = 8.75 → 9 bags of 3 ft³.
- At $4 a 2 ft³ bag that is $56; at $40 per bulk yard it is about $39 plus delivery.
Rule of thumb: once you need more than about 2 cubic yards (27 two-cubic-foot bags), bulk delivery is usually cheaper and much less work.
How much area does mulch cover?
| Depth | 2 ft³ bag covers | 1 yd³ covers |
|---|---|---|
| 1 in | 24 ft² | 324 ft² |
| 2 in | 12 ft² | 162 ft² |
| 3 in | 8 ft² | 108 ft² |
| 4 in | 6 ft² | 81 ft² |
Mulching tips from horticulture extensions
- Keep mulch 2–3 inches away from the stems of woody plants to avoid decay and rodent damage.
- Around trees, extend mulch at least 6–12 inches beyond the drip line where space allows.
- Avoid “volcano” mounding against trunks.
- Organic mulches break down over time, so plan to top up about an inch a year.
Guidance summarised from Clemson Cooperative Extension's mulch fact sheet.
Caveats and assumptions
- Bag sizes vary by brand; 2 ft³ is the most common in U.S. stores, with 1.5 ft³ and 3 ft³ also sold. Check the label.
- Fresh, fluffy mulch settles. If you are measuring depth right after spreading, aim slightly above your target.
- Pine straw is sold in bales by coverage area rather than volume; follow the bale label instead of this volume estimate.
- Rubber and stone mulches are much heavier and are usually applied at different depths.
Frequently asked questions
How many bags of mulch are in a yard?
One cubic yard is 27 cubic feet, so it equals 13.5 bags of 2 ft³ or 9 bags of 3 ft³.
How deep should mulch be?
For most wood and bark mulch, 2 to 3 inches. Clemson Extension warns that fine-textured mulches deeper than 2–3 inches can suffocate roots.
How many square feet does a bag of mulch cover?
A 2 cubic foot bag covers about 12 ft² at 2 inches or 8 ft² at 3 inches. Divide 24 by the depth in inches for any depth.
Is bagged or bulk mulch cheaper?
For small jobs bags are convenient. Above roughly 2 cubic yards, bulk mulch is usually cheaper per yard even after delivery. Enter both prices above to compare.
How much mulch do I need around a tree?
Select Circle and enter the diameter of the mulched ring. A 6 ft ring at 3 inches needs about 7 ft³, or four 2 ft³ bags.
Sources
- Clemson Cooperative Extension, Home & Garden Information Center — Mulch — recommended depths and placement
- NIST — Unit Conversion
This calculator gives estimates for planning and education. Check measurements, local codes, supplier specs and your school's official policy before relying on a result. See our disclaimer and how we build and check calculators.