Mulch Calculator
Enter the size of your beds and how deep you want the mulch, and see how many cubic yards or bags to buy — with a check against the recommended 2 to 4 inches.
Enter the size of the area and the depth.
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How to use the mulch calculator
- Measure each bed. Use Rectangle for straight beds and borders, Circle for rings around trees, and split curved beds into simple shapes you can add up.
- Choose the depth. For a new bed, use 3 inches. If there's still mulch from last year, measure what's left and only add the difference.
- Read the result in cubic yards (how bulk mulch is sold) and in 2 and 3 cubic foot bags (how garden centers sell it).
How to calculate mulch
Worked example: a 4 × 25 ft border, 3 inches deep
- Area: 4 × 25 = 100 sq ft
- Volume: 100 × 3 ÷ 12 = 25 ft³ = 0.93 yd³
- Bags: 25 ÷ 2 = 12.5, so 13 bags of 2 cu ft (14 with 5% extra), or 9 bags of 3 cu ft.
Worked example: a ring 6 ft across around a young tree, 3 inches deep
- Area: π × 3² = 28.3 sq ft
- Volume: 28.3 × 3 ÷ 12 = 7.1 ft³, so 4 bags of 2 cu ft. Leave a mulch-free gap of at least 4 inches around the trunk.
How much area does mulch cover?
| Depth | 1 cubic yard | One 2 cu ft bag | One 3 cu ft bag |
|---|---|---|---|
| 2 in | 162 sq ft | 12 sq ft | 18 sq ft |
| 3 in | 108 sq ft | 8 sq ft | 12 sq ft |
| 4 in | 81 sq ft | 6 sq ft | 9 sq ft |
One cubic yard equals 13.5 bags of 2 cu ft or 9 bags of 3 cu ft. Bulk mulch is normally sold by the yard, so compare the delivered price of bulk with the bag price once you pass a couple of yards.
How deep should mulch be?
University of Illinois Extension recommends a layer of 2 to 4 inches — 2 to 3 inches of composted or fine mulch, and 3 to 4 inches of coarse mulches such as wood chips and bark. More isn't better: thick layers can mat down, reduce the water and oxygen that reach the roots, and cause decay.
- Keep it off trunks and stems. Pull mulch at least 4 inches away from the trunk. "Volcano" mulching piled against the bark is one of the most common causes of tree decline.
- Top up, don't pile on. Check the depth before adding more. If there's still 2 inches, rake it to refresh the look and add only an inch.
- Go wide around trees. Spread mulch out toward the drip line rather than deep against the trunk.
Choosing a mulch
| Type | Good for | Keep in mind |
|---|---|---|
| Shredded hardwood | Beds and borders; knits together and stays on slopes | Breaks down in a year or two, feeding the soil |
| Pine bark nuggets | Decorative beds, acid-loving shrubs | Light pieces can float away in heavy rain |
| Wood chips | Around trees and on paths | Coarse, so use the 3–4 in end of the range |
| Pine needles | Slopes and acid-loving plants | Very light; sold by the bale rather than by volume |
| Compost | Vegetable and flower beds | Fine texture: 2–3 in is enough |
Frequently asked questions
How many bags of mulch are in a yard?
13.5 bags of 2 cubic feet, or 9 bags of 3 cubic feet. A cubic yard is 27 cubic feet.
How much mulch do I need for 100 square feet?
At 3 inches deep, 100 sq ft needs 25 cubic feet — about 0.93 cubic yards or 13 bags of 2 cu ft.
Should I remove old mulch before adding new?
Not usually. Measure the depth first: if the old layer is still 2 inches or more, just loosen it and add a thin top dressing. Remove it if it's matted, moldy or piled against trunks.
Does mulch settle?
Yes — fresh, fluffy mulch settles after the first rains, and organic mulch slowly breaks down. That's why the calculator adds a little extra by default.
Sources
- University of Illinois Extension, Proper mulching techniques — recommended depths and keeping mulch away from trunks.