What this tool does and when to use it
This calculator turns the size of your garden beds and the depth you want into the mulch volume in cubic yards or cubic meters, the number of 2 and 3 cubic foot bags (or 50 and 70 liter bags) and an approximate weight. It handles square, rectangular and round beds and several beds of the same size, and it also works for topsoil, compost and gravel.
How to calculate how much mulch you need
Mulch is sold by volume, so you need three numbers: the length and width of the bed and the depth you want to spread. The calculator above handles the unit conversions, but here is the math if you want to check it.
- Find the area. Multiply length by width. A 20 by 4 foot border is 80 square feet. For a round bed, multiply 3.14 by the radius squared.
- Convert the depth to feet. Divide inches by 12. Three inches is 0.25 feet.
- Work out the volume. Multiply area by depth. 80 times 0.25 is 20 cubic feet.
- Convert to yards or bags. Divide cubic feet by 27 for cubic yards, by 2 for 2 cubic foot bags or by 3 for 3 cubic foot bags. So 20 cubic feet is about 0.74 cubic yards, 10 small bags or 7 large bags.
In metric, multiply the area in square meters by the depth in meters. A 6 by 1.2 meter bed at 7.5 cm deep needs 0.54 cubic meters, which is 540 liters or 11 bags of 50 liters.
How much mulch for 100, 200, 500 or 1,000 square feet?
These figures come from the calculator above. Bags are rounded up to whole bags, so buy at least this many.
| Area | 2 in deep | 2 cu ft bags | 3 in deep | 2 cu ft bags |
|---|---|---|---|---|
| 100 sq ft | 0.62 cu yd | 9 | 0.93 cu yd | 13 |
| 200 sq ft | 1.23 cu yd | 17 | 1.85 cu yd | 25 |
| 300 sq ft | 1.85 cu yd | 25 | 2.78 cu yd | 38 |
| 400 sq ft | 2.47 cu yd | 34 | 3.70 cu yd | 50 |
| 500 sq ft | 3.09 cu yd | 42 | 4.63 cu yd | 63 |
| 1,000 sq ft | 6.17 cu yd | 84 | 9.26 cu yd | 125 |
Going from 2 to 3 inches deep needs half as much mulch again. From about 300 square feet at 3 inches, you are past the two cubic yard mark where bulk delivery usually beats bags on price.
How deep should mulch be?
| Where | Depth | Why |
|---|---|---|
| Flower beds and borders | 2 to 3 in (5 to 8 cm) | Blocks weeds and keeps moisture in without smothering plants |
| Around trees and shrubs | 3 to 4 in (8 to 10 cm) | Protects roots from heat and cold. Keep it off the trunk |
| Vegetable beds | 1 to 2 in (3 to 5 cm) | Use straw or compost, topped up through the season |
| Paths and play areas | 3 to 4 in (8 to 10 cm) | Stays springy and hides the soil beneath |
| Topping up existing mulch | 1 in (2 to 3 cm) | Refreshes color without building up too deep |
Bags or bulk: which is cheaper?
For small beds, bags are easier because you can carry them, store leftovers and choose from more colors. Once you need more than about two cubic yards, which is roughly 27 bags of 2 cubic feet, bulk delivery from a landscape yard is usually much cheaper per yard, even after the delivery fee. One cubic yard of mulch covers about 108 square feet at 3 inches deep, or 162 square feet at 2 inches.
Using the calculator for soil and gravel
The volume math is the same for any loose material, so you can use this tool for topsoil, compost, sand, pea gravel and decorative stone. Choose the material to see an approximate weight too, which matters when you are ordering by the ton or checking what your car or trailer can carry. Gravel weighs around 1.4 tons per cubic yard, several times more than bark mulch.
Filling new beds rather than topping them? The raised bed soil calculator works out soil and compost by the bag, and the plant spacing calculator tells you how many plants fit. Planning more garden work? Browse our small garden and backyard ideas and summer patio ideas for inspiration.
