How to use the mulch calculator
- Measure each bed's length and width in feet. For curved beds, use the average width, or split the bed into rectangles.
- Choose a depth in inches. The default is 3 in. See the depth guide below; most beds need 2 to 4 inches.
- Pick your bag size. It is printed on the bag in cubic feet. Common sizes are 1.5, 2 and 3 cu ft.
- Keep the waste/settling allowance (default 10%) or change it. Fresh mulch settles and spreads unevenly. Worked examples below show the exact volume before this allowance.
- Read the result in cubic yards (for bulk delivery), cubic feet, and number of bags (rounded up).
- For several beds, use the Several beds tab (up to four beds), or the multiple beds calculator. Round beds and tree rings have their own tabs.
Mulch formulas
- Cubic feet = length (ft) × width (ft) × depth (in) ÷ 12
- Cubic yards = cubic feet ÷ 27
- Bags = cubic feet ÷ bag size (cu ft), rounded up
- Area one bag covers = bag size × 12 ÷ depth (in)
- Area one cubic yard covers = 324 ÷ depth (in), because 27 ft³ × 12 = 324
Coverage at common depths
| Depth | 1 cubic yard covers | 2 cu ft bag covers | 1.5 cu ft bag covers |
|---|---|---|---|
| 2 in | 162 ft² | 12 ft² | 9 ft² |
| 3 in | 108 ft² | 8 ft² | 6 ft² |
| 4 in | 81 ft² | 6 ft² | 4.5 ft² |
Scotts' own table agrees with these numbers: one 1.5 cu ft bag at a 3 inch depth covers 6 ft².
Bags per cubic yard
| Bag size | Bags per yd³ |
|---|---|
| 1.5 cu ft | 18 |
| 2 cu ft | 13.5 |
| 3 cu ft | 9 |
This is the number to use when you compare bag prices with a bulk price per yard.
How deep should mulch be?
| Situation | Typical depth | Source |
|---|---|---|
| General beds, weed suppression | 2–3 in | Scotts mulch FAQ |
| Fine or composted mulch | 2–3 in | University of Illinois Extension |
| Coarse mulch, wood chips | 3–4 in | University of Illinois Extension |
| Maximum for most beds | 4 in | University of Vermont Extension: more than 4 in can encourage roots to grow from the trunk |
Keep mulch away from trunks and stems. Illinois Extension says to keep it at least 4 inches from a tree trunk, and spread it as a flat ring, not a cone.
Worked examples
A 20 × 5 ft bed at 3 inches
- 20 × 5 × 3 ÷ 12 = 25 ft³, which is 25 ÷ 27 = 0.93 yd³.
- Bags: 25 ÷ 2 = 12.5, so 13 × 2 cu ft bags. That's 17 × 1.5 cu ft or 9 × 3 cu ft.
Two beds, 30 × 4 ft and 10 × 10 ft, at 3 inches
- Area: 120 + 100 = 220 ft².
- Volume: 220 × 3 ÷ 12 = 55 ft³ = 2.04 yd³.
- That's 28 × 2 cu ft bags. At around two yards, bulk delivery is worth pricing.
A tree ring, 6 ft across, at 3 inches
- Area: π × 3² = 28.27 ft².
- Volume: 28.27 × 3 ÷ 12 = 7.07 ft³, so 4 × 2 cu ft bags.
- Leave the area next to the trunk bare, so the real amount is slightly less.
Topping up an existing bed
If the old mulch is still 1 inch deep and you want 3 inches, enter 2 inches as the depth, not 3. Scotts says old mulch doesn't usually need removing unless the layer is over 4 inches thick. Loosen it before adding the new layer.
Bags or bulk?
- Compare per cubic yard. Multiply the bag price by the bags-per-yard figure in the table above (13.5 for 2 cu ft bags) and compare that with the bulk price per yard plus delivery.
- Small jobs under about a yard usually go to bags. They are easy to carry and store, and clean to spread.
- Large jobs of several yards usually go to bulk, but ask about delivery fees and minimums, and make sure you have somewhere to tip the load.
We don't list prices because they vary by region, season and product.
Tips and common mistakes
- Divide inches by 12. Entering "3" as feet instead of inches overstates the volume 12 times.
- Measure every bed. Eyeballed beds are almost always bigger than they look.
- Round bags up. You can't buy part of a bag.
- Don't build "mulch volcanoes." University of Vermont Extension warns that mulch piled against trunks traps moisture and invites decay and pests.
- Keep it under 4 inches. Thicker layers can mat and keep water and air out, according to Illinois Extension.
- Re-mulch about once a year. Scotts recommends it as a general rule. Measure what's left before you buy.
- Allow for settling. Fresh mulch settles and spreads unevenly. Keep the waste allowance on, or buy one more bag than the exact count.
Frequently asked questions
How many bags of mulch are in a yard?
It depends on bag size: 18 × 1.5 cu ft, 13.5 × 2 cu ft, or 9 × 3 cu ft bags. A cubic yard is 27 cu ft.
How much area does a yard of mulch cover?
About 108 ft² at 3 inches deep, 162 ft² at 2 inches, or 81 ft² at 4 inches.
How many bags of mulch do I need for 100 square feet?
At 3 inches you need 25 ft³: 13 × 2 cu ft bags or 17 × 1.5 cu ft bags.
How deep should mulch be?
2 to 4 inches for most beds. Use 2–3 in for fine mulch and 3–4 in for coarse wood chips, per University of Illinois Extension.
Should I remove old mulch?
Usually not. Scotts says removal is only needed if the layer is thicker than about 4 inches. Otherwise loosen it and top up.
Can I use this for gravel or topsoil?
Yes. The volume math is the same. Use the gravel and topsoil versions for those defaults.
Sources
- Scotts Miracle-Gro, Mulch & Soil FAQs: 1.5 cu ft bag coverage at 3 in, a 2–3 in layer for weeds, removal over 4 in, mulch once a year. https://scottsmiraclegro.com/en-us/support/help-center/mulchessoils.html
- University of Illinois Extension, "Proper Mulching Techniques": 2–4 in depth, fine vs coarse, at least 4 in from the trunk. https://extension.illinois.edu/sites/default/files/proper%5Fmulching%5Ftechniques%5Finfosheet.pdf
- University of Vermont Extension, "Beware the Mulch Volcano": no more than 2–4 in; over 4 in encourages adventitious roots. https://www.uvm.edu/extension/news/beware-mulch-volcano
- NIST Handbook 44 (2026), Appendix C: 1 yd³ = 27 ft³. https://www.nist.gov/document/2026-nist-handbook-44-appendix-c