This mulch calculator turns a rectangular bed into a volume, then into bags. Enter the length and width in feet, the depth in inches, the bag size, and a waste allowance. The sample is a 10 foot by 20 foot bed, 3 inches deep, using 2 cubic foot bags and no extra for waste. The headline is 25 bags. The volume under that headline is 50 cubic feet, which is 1.852 cubic yards.
The arithmetic is the geometry of a rectangular prism, not a brand’s coverage claim, though the two agree when the bag is a true 2 or 3 cubic feet. One cubic yard is 27 cubic feet. Depth has to be converted from inches to feet before that division, and 12 times 27 is 324, so length times width times depth in inches, divided by 324, is the same yardage. A concrete slab uses a different bag. An 80 lb bag of concrete is about 0.60 cubic feet, and the concrete page on this site counts those bags. Do not use that bag count for mulch.
How to use this calculator
- Enter the length and the width in feet. The sample is 10 by 20. Measure the bed you will cover, not the whole yard.
- Enter the depth in inches. Three inches is a common finished depth for bark mulch. Type 3, not 0.25 feet. The form converts inches to feet.
- Choose a 2 cubic foot bag or a 3 cubic foot bag. Then enter a waste allowance from 0 to 100 percent. The sample is 0.
- Press Calculate. Read the bag count, the cubic feet and cubic yards, the coverage of one bag at this depth, and the bulk order rounded up to the next half yard.
How a bed becomes a bag count
Volume in cubic feet is length times width times depth, and the depth has to be in feet. Three inches is 3/12 of a foot, so a 10 by 20 bed at 3 inches is 10 × 20 × 3 / 12 = 50 cubic feet. Divide by 27 to get cubic yards. 50 / 27 is 1.8518…, shown as 1.852 cubic yards. The shortcut 10 × 20 × 3 / 324 is the same division, because the 12 in the depth and the 27 in the yard were folded together. Both paths describe a perfect rectangular layer. Real beds have tree trunks, curves, and a depth that is not uniform.
Bags are the volume divided by the size of one bag. A 2 cubic foot bag goes into 50 cubic feet exactly 25 times, so the headline is 25 bags and the line before rounding is 25 as well. A 3 cubic foot bag goes into the same 50 cubic feet 16.67 times, and the headline rounds up to 17 bags. You cannot buy two-thirds of a bag. When the division is exact, nothing extra is added. Coverage is the other direction of the same division. At 3 inches, a 2 cubic foot bag covers 2 × 12 / 3 = 8 square feet. The bed is 200 square feet, and 200 / 8 is 25 bags, which matches the headline.
Waste multiplies the volume before the bag count and before the bulk round-up. Ten percent turns 50 cubic feet into 55 cubic feet, or 2.037 cubic yards. Divided by 2, that is 27.5 bags, and the headline rounds up to 28. The bulk line then rounds 2.037 yards up to the next half yard, which is 2.5 cubic yards. That half-yard step is a common way bulk mulch is sold. It is not a second waste factor stacked on the 10%. If you buy bags, you do not also order the 2.5 yards. The two lines are alternative purchases of the waste-adjusted volume.
A thinner layer uses fewer bags only because each bag covers more ground. At 2 inches, a 2 cubic foot bag covers 12 square feet. The label on many 2 cubic foot bags states that 2-inch coverage, and 200 / 12 is 16.67, so the 10 by 20 bed needs 17 bags. At 1 inch the same bag covers 24 square feet and the bed needs 9 bags. At 4 inches it covers 6 square feet and the bed needs 34 bags. Depth is a choice about weeds and appearance, not a constant the calculator should hide.
Formula
Depth in feet = depth in inches / 12 Cubic feet = length (ft) × width (ft) × depth (ft) Cubic yards = cubic feet / 27 Same yards, depth kept in inches = length × width × depth / 324 Volume with waste = cubic feet × (1 + waste percent / 100) Bag size = 2 cubic feet, or 3 cubic feet Exact bags = volume with waste / bag size Bags to buy = exact bags, rounded up to the next whole bag Coverage of one bag = bag size × 12 / depth in inches, in square feet Bags per cubic yard, no waste = 27 / bag size, so 13.5 bags at 2 cubic feet and 9 bags at 3 cubic feet Bulk order = waste-adjusted yards, rounded up to the next 0.5 yard
The sample is exact, which makes the rounding visible by its absence. 10 × 20 × 3 / 12 is 50 cubic feet, not 49 or 51. 50 / 2 is 25 bags. 50 / 27 displayed to three decimals is 1.852 cubic yards. The bulk line rounds 1.852 up to 2 cubic yards. Ordering 2 yards for a bed whose geometry is 1.852 yards is the half-yard spare. It is not the same thing as typing a waste percent. With the waste field left at 0, the volume line and the waste line match, and only the bulk line has moved up.
Ten percent waste is 5 extra cubic feet on this bed, 27.5 bags before rounding, and a headline of 28. The no-waste bag line stays at 25 so you can see the waste separately from the round-up. Switch the bag to 3 cubic feet and leave the waste at 0: the yards stay 1.852, the exact bag count is 16.67, and the headline is 17. Coverage becomes 12 square feet per bag, because 3 × 12 / 3 is 12. A 3 cubic foot bag at 2 inches would cover 18 square feet. That is 3 × 12 / 2, and it is a different depth from the sample.
A small bed shows why the bulk round-up can be the wrong purchase. A 4 foot by 8 foot bed at 3 inches is 8 cubic feet, exactly 4 bags of the 2 cubic foot size, and 0.296 cubic yards. Rounded up to the next half yard, the bulk line says 0.5 cubic yards. Half a yard is 13.5 cubic feet, far more than the 8 cubic feet the bed holds. Four bags are the useful order. The half-yard line is there so the arithmetic stays visible, not as advice to schedule a delivery for a bed that fits in a car.
Worked mulch examples
10 by 20 feet, 3 inches deep, 2 cubic foot bags, no waste
The headline is 25 bags (2 cu ft). Bed volume is 50 cubic feet, or 1.852 cubic yards. Bags before rounding up are 25. The bulk order is 2 cubic yards. Coverage at this depth is 8 square feet per 2 cubic foot bag. Those 25 bags and the 2 yards are two ways to buy a volume that started at 1.852 yards. Buying both covers the bed twice and leaves a pile over. The half yard you did not need, if you choose bags, is the reason the bag line and the bulk line are not equal volumes.
Check it from the coverage side. Two hundred square feet divided by 8 square feet per bag is 25 bags. Check it from the yard side. One cubic yard takes 13.5 bags of this size, and 1.8518 yards times 13.5 is 25 bags. The three routes meet because they are the same geometry. If your bag says 1.5 cubic feet, or 1 cubic foot, this headline will not match the pallet. The form only offers 2 and 3.
The same bed with 10% waste, and in 3 cubic foot bags
Set the waste to 10 and keep the 2 cubic foot bag. The headline is 28 bags (2 cu ft). Volume with waste is 55 cubic feet, or 2.037 cubic yards. Bags before rounding up are 27.5. Bags with no waste allowance, rounded up, stay at 25. The bulk order is 2.5 cubic yards. The jump from 25 bags to 28 is the 2.5 extra bags of waste, then a round-up from 27.5 to 28. It is not a second 10% applied after the round-up.
Return the waste to 0 and choose the 3 cubic foot bag. The headline is 17 bags (3 cu ft). Cubic yards do not change. Bags before rounding up are 16.67. Coverage is 12 square feet per bag, and 200 / 12 is the same 16.67. Nine of these bags fill a cubic yard, because 27 / 3 is 9, whereas the 2 cubic foot bag took 13.5. Trust the 17 the form shows. Do not rescale the 25 by a rough ratio and then round a second time.
Changing the depth, and a bed that is an exact four bags
On the 10 by 20 foot bed with 2 cubic foot bags and no waste, 1 inch of mulch is 9 bags and 0.617 cubic yards, with a bulk line of 1 cubic yard. Two inches is 17 bags and 1.235 cubic yards. Three inches is the sample, 25 bags. Four inches is 34 bags and 2.469 cubic yards, with a bulk line of 2.5. The 2-inch row is the one a bag label usually prints, 12 square feet of coverage. The 3-inch row is 8 square feet. Using the 12-square-foot claim on a bed you intend to spread 3 inches deep will leave you short by the difference between 17 and 25 bags.
A 4 by 8 foot bed at 3 inches and a 2 cubic foot bag is 8 cubic feet and exactly 4 bags. The yardage is 0.296, and the bulk line rounds it to 0.5 cubic yards. Order the 4 bags. The concrete calculator’s 10 by 10 by 4 inch slab is a different material and a different yield: about 1.235 cubic yards and 56 bags of 80 lb concrete with no waste. That 56 is not a mulch count, and this 25 is not a concrete count.
Bags for a 10 by 20 foot bed
| Depth | Cubic yards | 2 cu ft bags | Coverage per bag | Bulk order |
|---|---|---|---|---|
| 1 inch | 0.617 | 9 | 24 sq ft | 1 cubic yard |
| 2 inches | 1.235 | 17 | 12 sq ft | 1.5 cubic yards |
| 3 inches | 1.852 | 25 | 8 sq ft | 2 cubic yards |
| 4 inches | 2.469 | 34 | 6 sq ft | 2.5 cubic yards |
What a rectangular mulch count leaves out
The bed is a rectangle of one depth. A curved bed, a ring around a tree, a slope, and a depth that tapers at the edge are different volumes. Tree trunks and stepping stones displace a little mulch. The waste field is the place to allow for that, and for a pile that never quite leaves the wheelbarrow. Ten percent is a planning allowance, not a rule. A careful spread on a flat bed may come in under it.
Bag sizes are the nominal 2 and 3 cubic feet. Some bags are sold by weight, and a wet bag or a coarsely shredded product can fill less ground than the nominal volume. Read the volume printed on the bag. If it is not 2 or 3 cubic feet, divide the cubic-foot line by that volume yourself. Colour, dye, and the species of wood do not change the geometry. They change the price and how the mulch settles, which this page does not estimate.
The bulk line rounds up to the next half yard because many landscape yards sell that way. A yard with a one-yard minimum, or a delivery fee that swamps a small order, will not honor a 0.5 yard request just because this page printed one. The 4 by 8 foot example is the case to watch: 4 bags are a closer match than half a yard. Cubic yards here are US survey-style customary yards of 27 cubic feet. A UK or Australian supplier selling by the cubic metre needs a conversion. One cubic yard is about 0.765 cubic metres. The bag headline itself is not a metric bag.
Nothing on this page is a planting recommendation. Three inches is a common depth for suppressing weeds in an ornamental bed, and it can be too much against a trunk or too little on a path. The concrete page is the one that counts 40, 60, and 80 lb bags of concrete. The paint page counts gallons from square feet. A mulch volume will not answer either of those.
Frequently asked questions
How many bags of mulch cover a 10 by 20 foot bed at 3 inches?
With 2 cubic foot bags and no waste, 25 bags. The bed is 50 cubic feet, or 1.852 cubic yards, and each bag covers 8 square feet at that depth. A 3 cubic foot bag on the same bed comes out to 16.67 bags, which rounds up to 17.
What is the difference between a 2 cubic foot and a 3 cubic foot bag of mulch?
The 3 cubic foot bag holds half again as much. It takes 13.5 of the smaller bags to fill a cubic yard, and 9 of the larger ones. On the sample bed the headlines are 25 and 17. The cubic yards do not change when you change the bag.
Why do mulch calculators divide by 324?
Length and width are in feet and the depth is in inches. Dividing the depth by 12 makes feet, and dividing cubic feet by 27 makes yards. Multiplying those divisors gives 324. The sample is 10 × 20 × 3 / 324, which is 1.852 cubic yards, the same figure as 50 cubic feet divided by 27.
Should I buy the mulch bags and the bulk cubic yards?
No. They are two ways to buy one volume. The sample is 25 bags or a bulk order of 2 cubic yards, not both. With 10% waste it is 28 bags or 2.5 cubic yards. The bulk line has already rounded up. Adding the bags on top of it double-counts the bed.
How many square feet does one 2 cubic foot bag cover at 3 inches?
Eight. At 2 inches the same bag covers 12 square feet, which is the figure many labels print. At 4 inches it covers 6. Using the 2-inch claim on a 3-inch job undercounts the bags. On this 200 square foot bed that mistake is 17 bags instead of 25.
Related ClearCalc pages
- Gravel calculator The same 10 by 20 foot area at 3 inches is 1.852 cubic yards, then 2.625 short tons of dry gravel. Mulch stops at the bags.
- Concrete slab calculator 80, 60, and 40 lb bags for a pour. A 10 by 10 slab at 4 inches is not this mulch count.
- Room paint calculator Gallons from wall area. It does not estimate a bed.
- Length converter from meters If the bed was measured in meters, convert to feet before you type the length and width. Depth stays in inches here.