How to use the mulch calculator
- Measure each bed. Choose its shape: a rectangle (length and width), a circle (the distance across, through the middle) or a triangle (the base, and the height measured square to the base). Press Add another bed for each extra bed; the beds are added together.
- Enter the depth of mulch you want to spread, in inches, or in centimeters if you measure in meters.
- Optional: add a percentage extra, and the size printed on the bag you plan to buy.
The result shows cubic yards, cubic feet, cubic meters and liters, and how many bags to buy, rounded up. In feet it counts 2 and 3 cubic foot bags. In meters it counts 50 and 60 liter bags.
How deep should mulch be?
Extension services give a range rather than one number, because it depends on the mulch. Clemson Cooperative Extension's fact sheet on mulch says:
- Fine wood and bark mulches "should not be more than 2 to 3 inches deep".
- Coarse mulch such as pine bark nuggets "can be as deep as 4 inches".
- Grass clippings or shredded leaves "should never be deeper than 2 inches".
- "A 1-inch layer of small rocks will provide good weed control."
For UK gardens, the Royal Horticultural Society says:
"To be effective, biodegradable mulches need to be between at least 5cm (2in) and ideally 7.5cm (3in) thick"RHS, Mulches and mulching
Both warn against piling mulch against plants. Clemson says to keep mulch 2 to 3 inches away from the stems of woody plants, and for new trees, "do not pile mulch against the trunk". The RHS says mulch touching the stems of trees or shrubs can soften them and make them open to disease. Clemson also notes that too much fine mulch "can suffocate plant roots". The calculator shows a note if you enter more than 4 inches (about 10 cm).
If a bed already has old mulch on it, measure what is there and enter only the depth you are adding.
How the mulch amount is worked out
Each bed's area comes first: length x width for a rectangle, 3.14159 x diameter x diameter / 4 for a circle, and base x height / 2 for a triangle. The areas are added, then:
cubic feet = square feet x depth in inches / 12cubic yards = cubic feet / 27
Put together, cubic yards = square feet x inches / 324. Clemson gives the same figure the other way round: "One cubic yard will cover a 324-square-foot area with an inch of mulch."
Example (press Try an example): a border 20 ft by 4 ft plus a round bed 6 ft across, both 3 inches deep.
| Step | Working | Result |
|---|---|---|
| Border | 20 x 4 | 80.00 sq ft |
| Round bed | 3.14159 x 6 x 6 / 4 | 28.27 sq ft |
| Total area | 80 + 28.27 | 108.27 sq ft |
| Cubic feet | 108.27 x 3 / 12 | 27.07 cu ft |
| Cubic yards | 27.07 / 27 | 1.00 cu yd |
| 2 cu ft bags | 27.07 / 2 = 13.5 | 14 |
| 3 cu ft bags | 27.07 / 3 = 9.02 | 10 |
Bags are always rounded up, since a store sells whole bags, but an exact answer is not: 6 cubic feet is exactly three 2 cu ft bags.
How much area a cubic yard or a bag covers
The same arithmetic run backwards tells you how far a load will go.
| Depth | 1 cubic yard | 2 cu ft bag | 3 cu ft bag |
|---|---|---|---|
| 1 inch | 324 sq ft | 24 sq ft | 36 sq ft |
| 2 inches | 162 sq ft | 12 sq ft | 18 sq ft |
| 3 inches | 108 sq ft | 8 sq ft | 12 sq ft |
| 4 inches | 81 sq ft | 6 sq ft | 9 sq ft |
Measuring in meters, and UK bags in liters
Choose Meters and give the depth in centimeters. The volume is square meters x centimeters / 100 = cubic meters, and one cubic meter is 1,000 liters, which is how UK bags are labeled. Example: a border 6 m by 1.2 m plus a round bed 2 m across, 7.5 cm deep.
| Step | Working | Result |
|---|---|---|
| Total area | 7.20 + 3.14 | 10.34 m² |
| Volume | 10.34 x 7.5 / 100 | 0.78 m³, 776 liters |
| 50 liter bags | 775.6 / 50 = 15.5 | 16 |
| 60 liter bags | 775.6 / 60 = 12.9 | 13 |
At 5 cm deep, a 50 liter bag covers 1 m² and a 60 liter bag covers 1.2 m². At 7.5 cm, they cover about 0.67 m² and 0.8 m².
Odd shapes and other things to check
- Curved or irregular beds: split them into rectangles, circles and triangles that roughly fit, and add each as its own bed. For a bed around a tree, the trunk takes up little room and can be ignored.
- Settling: fresh, fluffy mulch settles after it is spread and watered. If you want the depth after settling, add a little extra with the Extra box. How much is your call; no fixed figure applies to every mulch.
- Bag sizes: the figure on the bag is what counts. Check it before you buy, and enter it if it is not one of the sizes shown.
For concrete, or for a single slab or hole, the cubic yard calculator does the same volume maths with concrete bag counts. For stone, the gravel calculator also gives the weight in tons.
Questions and answers
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet, so it is 13.5 bags of 2 cu ft (buy 14) or 9 bags of 3 cu ft.
How much area does a yard of mulch cover?
Clemson Extension says one cubic yard covers 324 square feet at 1 inch deep. That is 162 sq ft at 2 inches, 108 sq ft at 3 inches and 81 sq ft at 4 inches.
How deep should I spread mulch?
Clemson Extension says fine wood and bark mulches should not be more than 2 to 3 inches deep, and coarse pine bark nuggets can be up to 4 inches. The RHS advises at least 5 cm (2 in) and ideally 7.5 cm (3 in). Keep mulch off trunks and stems.
How many 2 cubic foot bags of mulch do I need?
Work out the cubic feet (square feet x depth in inches / 12) and divide by 2, rounding up. A 10 ft by 10 ft bed 3 inches deep needs 25 cubic feet, which is 13 bags.
How much mulch does a circle around a tree need?
Choose Circle and enter the distance across. A ring 8 ft across, 3 inches deep, is 3.14159 x 8 x 8 / 4 = 50.27 sq ft, which needs 12.57 cubic feet, or 7 bags of 2 cu ft. Keep the mulch a few inches clear of the trunk.
Sources
Checked on 22 October 2026. If a rule has changed, please tell us.