Mulch Calculator
Enter the size of the bed and how deep you want the mulch. You get the volume in cubic yards for bulk delivery, in cubic feet, and the number of bags if you are buying it by the bag.
How much mulch do I need?
Multiply the area of the bed in square feet by the depth in feet, then divide by 27 for cubic yards. At the usual 3 in depth, one cubic yard covers 108 sq ft and one 2 cu ft bag covers 8 sq ft. A 20 ft x 10 ft bed is 200 sq ft, which takes 50 cu ft, or 1.85 cubic yards, or 25 bags.
Mulch you need
200 sq ft at 3 in deep is 50 cu ft, or 25 bags of 2 cu ft.
- Area mulched
- 200 sq ft
- Volume
- 50 cu ft
- Bags
- 252 cu ft bags
The numbers above are a worked example for a 20 ft x 10 ft bed at 3 in deep. Allow this page to run scripts in your browser to use your own dimensions, or follow the formula further down the page and do it by hand.
How the mulch calculator works, step by step
Mulch is sold by volume, but you buy it to cover an area at a certain depth. So every mulch estimate is the same conversion: turn an area and a depth into a volume, then express that volume in whatever unit your supplier sells in. There is no coverage rate to look up and no product-specific figure involved. It is pure geometry, which is why this page can show you the whole calculation.
For a circular bed or a tree ring, use area = 3.1416 x radius squared, where the radius is half the diameter. A 12 ft circle is 3.1416 x 6 x 6 = 113 sq ft.
This is the step people skip, and it is the reason estimates come out twelve times too big. Three inches is 0.25 ft, not 3 ft.
bags = volume (cu ft) / 2
There are 27 cubic feet in a cubic yard, because a yard is three feet on each side and 3 x 3 x 3 = 27. Bags are almost always 2 cu ft, though some brands sell 1.5 cu ft or 3 cu ft bags. Check the bag before you divide.
Worked example: a 20 ft x 10 ft bed at 3 in deep
- Area: 20 x 10 = 200 sq ft
- Depth: 3 / 12 = 0.25 ft
- Volume: 200 x 0.25 = 50 cu ft
- Cubic yards: 50 / 27 = 1.85 cu yd
- Bags: 50 / 2 = 25 bags
How deep should mulch be?
Deeper is not better. Wood and bark mulches are made of fine particles, and a thick layer holds water against the soil surface and starves the roots underneath of air. Clemson's Home & Garden Information Center puts the limit plainly: fine-textured wood and bark mulches should not be more than 2 to 3 inches deep, and too much of them suffocates roots and yellows the plant.
| Situation | Depth | Why |
|---|---|---|
| Bark and fine wood mulch in beds | 2 to 3 in | Any deeper and air stops reaching the roots |
| Topping up an existing bed | 1 to 2 in | Measure what is already there and make up the difference |
| Coarse chips or nuggets | 3 to 4 in | Bigger particles leave air gaps, so depth is less risky |
| Around a tree trunk | 0 in | Pull mulch back from the trunk; volcano mulching rots the bark |
| Paths and play areas | 4 to 6 in | Compaction and foot traffic, not plant health, set the depth |
One practical consequence for your order: if a bed already has an inch of old mulch in it, you are buying the difference, not the full depth. Measure with a trowel before you order rather than after.
Bags or bulk delivery?
The arithmetic is simple. A cubic yard is 27 cu ft, so it is 13.5 bags of 2 cu ft. Bulk mulch is usually a third to a half the price per cubic yard once you pass a load worth delivering, but it arrives as a pile on your driveway and you move it with a wheelbarrow.
| Volume | Bags of 2 cu ft | Usually cheaper as |
|---|---|---|
| 0.5 cu yd | 7 | Bags |
| 1 cu yd | 14 | Bags, unless delivery is free |
| 2 cu yd | 27 | Either; compare the delivery fee |
| 3 cu yd | 41 | Bulk |
| 5 cu yd | 68 | Bulk, clearly |
Many suppliers sell bulk by the scoop rather than the yard, and a scoop is not a standard unit. Ask how many cubic yards their scoop holds before you compare prices, and enter that figure in the calculator to get the number of scoops to order.
Cases the simple formula does not cover
Beds that are not rectangles or circles
Break the bed into rectangles, triangles and half-circles, work out each one, and add them up. A curved border bed is usually close enough to a long rectangle using the average width: pace the width at several points, average them, and multiply by the length.
Slopes
A slope has more surface than its footprint. For a gentle bank the difference is small enough to ignore; for anything steeper than about one in three, add 10 to 15 % and expect mulch to migrate downhill. Shredded mulch knits together and stays put on a slope. Nuggets do not.
Mulch that settles
Fresh mulch settles by roughly 10 to 20 % in the first season. Spread to the finished depth you want now; do not pre-compensate by going deeper, because the depth limit above applies to the freshly spread layer.
Rubber and stone
Rubber mulch and decorative stone are sold by weight as often as by volume. For stone, use the gravel calculator, which converts volume to tons.
Frequently asked questions
How many bags of mulch in a cubic yard?
Thirteen and a half. A cubic yard is 27 cubic feet and a standard bag holds 2 cubic feet, so 27 / 2 = 13.5 bags. In practice you buy 14. If your bags are 1.5 cu ft it is 18 bags, and if they are 3 cu ft it is 9.
How much does a cubic yard of mulch cover?
108 square feet at 3 inches deep, 162 sq ft at 2 in, and 81 sq ft at 4 in. The rule behind all three: divide 324 by the depth in inches to get the square footage one cubic yard covers.
How much does a 2 cubic foot bag of mulch cover?
8 square feet at 3 inches deep, or 12 sq ft at 2 in. A bag holds 2 cu ft, and 2 divided by a quarter of a foot is 8.
How deep should mulch be?
2 to 3 inches for bark and shredded wood mulch. Deeper layers of fine mulch stop air reaching the roots. Coarse chips and nuggets tolerate 3 to 4 inches because the particles leave gaps. Keep all of it away from tree trunks and plant stems.
How much mulch for a 1000 square foot bed?
At 3 in deep, 1000 sq ft takes 250 cu ft, which is 9.26 cubic yards or 125 bags. At that size bulk delivery is far cheaper, and you should expect to spend a full day moving it.
Should I remove the old mulch first?
Usually not. Old mulch breaks down into the soil, which is half the point of using it. Rake it level, break up any crust, measure what remains, and top up to the depth you want. Remove it only if it has matted into a water-repellent layer or if the total depth has crept past 3 inches.
When is the best time to mulch?
Mid to late spring, once the soil has warmed. Mulching too early insulates cold soil and slows everything down. A second, lighter application in autumn protects roots over winter in cold regions.
Source
Depth guidance on this page comes from Clemson Cooperative Extension, Home & Garden Information Center, Mulch (HGIC 1604). The volume arithmetic is not product-specific: it is the definition of a cubic yard and a cubic foot, so there is no coverage rate to go out of date. The only figure you should check against your own purchase is the size of the bag, which is printed on it.