How to use the mulch calculator
Pick Imperial or Metric at the top of the form, then add each bed by its shape and size in feet or meters. Choose how deep you want the mulch, or tap one of the three common depths. The calculator adds your beds together and shows cubic yards, cubic feet and the number of bags for each common bag size. Type in a bulk price and a bag price if you want to see which one costs less for your job.
How it's figured
Mulch is sold by volume, so the calculator multiplies the area of your beds by the depth and converts the answer. Area is in square feet, depth is in inches, and one cubic yard is 27 cubic feet.
cubic meters = square meters × depth in centimeters ÷ 100
Take a bed 10 ft by 12 ft with 3 inches of mulch. The area is 120 square feet. Times 3 inches divided by 12 gives 30 cubic feet. Divide by 27 and you get 1.11 cubic yards. In 2 cubic foot bags that is 30 ÷ 2 = 15 bags.
In metric, a bed 3 m by 4 m with 7.5 cm of mulch is 12 square meters × 0.075 m = 0.9 cubic meters, or 900 liters. In 50 liter bags that is 900 ÷ 50 = 18 bags.
Circles use π × radius squared, and triangles use half the base times the height. If you already know the area, pick that option and type it in directly. This calculator does not add extra for settling unless you ask for it. Fresh mulch compacts and breaks down, and thin spots show up at the edges, so many people order 5 to 10 percent more than the exact number.
| Bag size | Bags in one cubic yard |
|---|---|
| 1.5 cubic feet | 18 |
| 2 cubic feet | 13.5 |
| 3 cubic feet | 9 |
How deep should mulch be?
For a bed that already has mulch, 2 inches tops it up. For a new bed or bare soil, use 3 inches. Go to 4 inches only where weeds are a serious problem. Deeper than that rarely helps, and a thick layer can hold too much water against roots.
Keep mulch off the trunks of trees and shrubs and away from house siding. Mulch piled against bark stays damp, which invites rot and pests. Pull it back a few inches and spread it thinner near the stem, like a doughnut and not a volcano.
Where the numbers come from
- 27 cubic feet per yard. A cubic yard is 3 ft by 3 ft by 3 ft, so 27 is a definition and not an estimate.
- Bag sizes. The volumes of 1.5, 2 and 3 cubic feet are the sizes printed on US retail bags. In Metric the page uses 50, 80 and 100 liter bags, the sizes sold in the UK and Europe. Check the label, because some brands use different sizes.
- Depth advice. University extension services commonly recommend about 2 to 4 inches of mulch, and the three depth buttons follow that range.
- Weight. Dry wood mulch commonly weighs about 300 to 700 pounds per cubic yard, pine bark at the light end and hardwood at the heavy end, and rain can add half again as much. The calculator uses a dry planning weight for the type you pick (450 if you are not sure), so ask your supplier before loading a truck. Rubber mulch is much heavier and is not covered here.
- Coverage. One cubic yard covers 324 square feet at 1 inch deep, which follows from 27 cubic feet times 12 inches.
- Metric. The Imperial | Metric switch changes what you type and what you see; the math is the same. A foot is exactly 0.3048 m and an inch exactly 2.54 cm, so a cubic yard is exactly 0.764554857984 cubic meters and a cubic foot is 28.316846592 liters. A pound is exactly 0.45359237 kg. Bags are shown in the cubic feet printed on U.S. bags, with the liters beside them.
- Prices. Prices come from you. The calculator does not guess what mulch costs where you live.
Bulk or bagged?
To compare the two, convert the bag price to a price per cubic yard: bag price ÷ bag size × 27. A bag that costs $5 for 2 cubic feet works out to $67.50 per cubic yard, which you can set against a bulk quote. Bags suit small jobs, tight access and mixed colors. Bulk is often cheaper per yard for larger jobs, but add the delivery fee, any minimum load and the time to move a pile. The cost box above does this math once you enter both prices.
Common mistakes
The first is forgetting what sits inside a bed. Stepping stones, a boulder or a birdbath take up room that mulch does not need, so subtract their area and enter the net figure with the square feet option. The second is mixing bag sizes. A 1.5 cubic foot bag and a 3 cubic foot bag are priced very differently, so compare the price per cubic foot. The third is using one depth for everything. A path needs less than a bed of perennials, so run the calculator once for each depth and add the results.
Uses beyond flower beds
The same math covers tree rings, garden paths, vegetable garden walkways, slopes that need erosion cover and the area under a deck or play set. Playgrounds need a certified surface material, so use the volume here only as a starting point and follow the product's depth rules.
Questions
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet. That is 18 bags of 1.5 cubic feet, 13.5 bags of 2 cubic feet, or 9 bags of 3 cubic feet.
How much area does a cubic yard of mulch cover?
At 3 inches deep it covers about 108 square feet. At 2 inches it covers 162 square feet, and at 4 inches it covers 81.
How much does a cubic yard of mulch weigh?
Dry wood mulch commonly weighs about 300 to 700 pounds: pine bark about 375, cedar about 425 and hardwood about 575. Wet mulch can weigh half again as much. Your supplier can tell you the weight of the product you are buying.
Can I use metric?
Yes. Tap Metric at the top of the form and type your beds in meters, centimeters or millimeters and the depth in centimeters (5, 7.5 and 10 cm are the three common depths). You get cubic meters, liters, bags of 50, 80 or 100 liters and the weight in kilograms. You can still type 12 ft or 3 in into any box, and the page remembers your choice.
Do I need landscape fabric under mulch?
Not always. Fabric slows some weeds, but it can also trap water and make future planting harder. Many gardeners skip it and use a deeper layer of mulch instead.
When should I spread mulch?
Spread it after the soil has thawed and been cleared of weeds, and top it up when the layer wears thin. Avoid adding a fresh thick layer on top of an old thick one.