Mulch Calculator
This mulch calculator tells you how many bags of mulch, or how many cubic yards in bulk, you need to cover a garden bed or tree ring at the depth you want. It also works for bagged topsoil and compost.
Result
13 bags of mulch
| Bag size | 2 cu ft |
|---|---|
| Volume (bulk) | 0.93 yd³ (25 ft³) |
| Area covered | 100 ft² |
Results update as you type.
How Much Mulch Do I Need?
Mulch is sold by volume. Bags are labeled in cubic feet and bulk mulch is sold by the cubic yard. To work out how much you need, find the area of the bed, multiply by the depth, and convert the result to bags or yards. The calculator does this in one step. The formulas are below if you want to check them.
How to Calculate Mulch by Hand
Rectangular beds
Volume (ft³) = length (ft) × width (ft) × (depth (in) ÷ 12)
Round beds and tree rings
Volume (ft³) = 3.1416 × (diameter (ft) ÷ 2)² × (depth (in) ÷ 12)
Convert to bags or yards
- Bags = volume ÷ bag size, rounded up (2 cu ft is the most common bag)
- Cubic yards = volume ÷ 27
Worked example: a foundation bed and a tree ring
You’re mulching a bed along the front of the house, 40 feet long and 4 feet deep from the wall. There’s also a ring around a young maple, 6 feet across. Both get 3 inches of mulch.
- Bed: 40 × 4 × (3 ÷ 12) = 40 ft³
- Tree ring: 3.1416 × 3² × (3 ÷ 12) = 7.07 ft³
- Total: 47.07 ft³, or 1.74 cubic yards
- In 2 cu ft bags: 47.07 ÷ 2 = 23.5, rounded up to 24 bags
At almost two yards, it’s worth getting a bulk delivery quote too.
Tips & Common Mistakes
Break odd shapes into simple ones
Curved beds rarely match a perfect rectangle. Split the bed into a few rectangles and circles, run each through the calculator, and add the volumes together. A small overestimate is fine, because leftover mulch keeps well in the bag.
Don’t pile mulch against trunks
“Volcano” mulching, where mulch is heaped up a tree trunk, holds moisture against the bark and invites rot and rodents. Spread it wide and flat. Extension services suggest 3 to 6 feet out from the trunk around trees, pulled back a few inches from the bark itself.
Thicker isn’t better
Past about 4 inches, mulch can mat down and keep water and air from reaching the roots. If you’re topping up an existing bed, measure what’s there first and only add the difference.
Bulk delivery needs a drop spot
A yard or more of bulk mulch is a big pile. Pick a spot the truck can reach, preferably on a tarp or a part of the driveway you don’t mind sweeping. Have a wheelbarrow and a pitchfork or mulch fork ready.
Mixing topsoil or compost into beds
Use the same math to top-dress a bed with compost or fill a raised bed with soil. Choose the bag size that matches the product. Bagged topsoil and garden soil often come in 0.75 or 1 cu ft bags. For rock or gravel, use our gravel calculator, which also gives the weight in tons.
Frequently Asked Questions
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet. That works out to 13.5 bags of the common 2 cubic foot size, so buy 14 bags. With 3 cubic foot bags you need 9, and with 1.5 cubic foot bags you need 18.
How deep should mulch be?
University extension services generally recommend 2 to 4 inches. Use the thinner end for fine or composted mulch and the thicker end for coarse bark around trees and shrubs. Keep mulch a few inches back from tree trunks and plant stems so it doesn't hold moisture against the bark.
How much area does a 2 cubic foot bag of mulch cover?
A 2 cubic foot bag covers about 8 square feet at 3 inches deep, 12 square feet at 2 inches, or 6 square feet at 4 inches. Divide 24 by the depth in inches to get the square feet one bag covers.
How much mulch do I need for 100 square feet?
At 3 inches deep, 100 square feet takes 25 cubic feet of mulch. That is about 0.93 cubic yards, or 13 bags of 2 cubic feet each. At 2 inches deep it is 16.7 cubic feet, or 9 bags.
Is it cheaper to buy mulch in bags or in bulk?
For small beds, bags are simpler and there is no delivery fee. Once a job reaches a cubic yard or two, bulk mulch from a landscape supplier usually costs less per yard, even with delivery. Bulk also saves you from disposing of dozens of plastic bags.
Should I remove old mulch before adding new mulch?
Not usually. Measure how deep the old layer is and only top up to your target depth. If 1 inch is left and you want 3 inches, enter a depth of 2 inches. Rake out old mulch that has matted into a crust so water can get through.
Can I use this calculator for topsoil or compost?
Yes. The volume math is the same. Pick the 0.75 or 1 cubic foot bag size to match bagged topsoil or compost, or use the cubic yards figure if you are ordering bulk soil for raised beds or leveling.
Related Calculators
Sources & Assumptions
- University of Illinois Extension, Proper Mulching Techniques — 2 to 4 inch layer; composted materials 2 to 3 inches
- Mississippi State University Extension, How to Mulch — 3 to 4 inches around trees, kept off the trunk
- Bag sizes (0.75, 1, 1.5, 2 and 3 cu ft) are the volumes printed on common retail bags. Check yours.
- Volumes are rounded only for display. Bag counts always round up.
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