Type the length, width and depth of your garden bed. The tool tells you how many cubic yards to order in bulk, or how many 2 or 3 cubic foot bags to buy, with metric cubic meters and 50 liter bags as well.
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This mulch calculator is for gardeners and homeowners topping up flower beds, tree rings and borders. It multiplies the bed area by the depth you want, then shows the answer as bulk cubic yards, as bag counts for the common bag sizes, and in cubic meters for metric buyers.
How Do You Calculate How Much Mulch You Need?
Multiply the bed length by width to get square feet, multiply by the depth in inches, and divide by 324 to get cubic yards. A 12 ft by 8 ft bed at 3 inches deep is 96 × 3 ÷ 324 = 0.89 cubic yards, which is 24 cubic feet, or 12 bags of 2 cubic feet.
What Is the Formula for Mulch?
The mulch formula is cubic yards = area in square feet × depth in inches ÷ 324, because one cubic yard spread 1 inch deep covers 324 square feet. That number comes from 27 cubic feet in a cubic yard times 12 inches in a foot.
cubic yards = cubic feet ÷ 27 (or area × depth ÷ 324)
bags = cubic feet ÷ bag size, rounded up
cubic meters = length (m) × width (m) × depth (cm) ÷ 100
Garden centers sell bulk mulch by the cubic yard and bagged mulch by the cubic foot, most often 2 or 3 cubic feet per bag. In the UK and Europe, bags are labeled in liters, and 1 cubic meter is 1,000 liters. For a round tree ring, find the area with π × radius squared, which the circle calculator does for you, and enter the area as length with a width of 1.
How Deep Should Mulch Be?
Most garden beds need 2 to 4 inches (5 to 10 cm) of mulch, according to University of Illinois Extension. Fine composted mulch works at 2 to 3 inches and coarse wood chips at 3 to 4 inches. Keep mulch at least 4 inches away from tree trunks, because mulch piled against bark, often called a mulch volcano, keeps the bark wet and invites rot and pests. Too deep a layer can also starve roots of air.
How Much Area Does a Cubic Yard of Mulch Cover?
One cubic yard of mulch covers 324 square feet at 1 inch deep, 162 at 2 inches, 108 at 3 inches and 81 at 4 inches. Bag coverage follows the same math:
| Depth | 1 cubic yard | 2 cu ft bag | 3 cu ft bag |
|---|---|---|---|
| 1 in | 324 ft² | 24 ft² | 36 ft² |
| 2 in | 162 ft² | 12 ft² | 18 ft² |
| 3 in | 108 ft² | 8 ft² | 12 ft² |
| 4 in | 81 ft² | 6 ft² | 9 ft² |
Should You Buy Mulch in Bags or Bulk?
Bulk is usually cheaper once you need more than about 1 to 2 cubic yards, since one cubic yard equals 13.5 bags of 2 cubic feet. Bags are easier to carry, store and spread in small beds. Common types include shredded hardwood, pine bark, wood chips and straw, and all are organic mulch that breaks down and feeds the soil over a year or two. If your bed has an odd shape, measure it in parts with the square footage calculator, and the cubic yard calculator works for soil and compost.
Worked Example
Maria has a flower bed 12 ft long and 8 ft wide and wants 3 inches of mulch. The area is 96 square feet, and the tool shows 96 × 3 ÷ 12 = 24 cubic feet, or 0.89 cubic yards. In bags that is 12 bags of 2 cu ft or 8 bags of 3 cu ft. A UK gardener with a 4 m by 2.5 m border at 7.5 cm deep gets 0.75 m³, or 750 liters, which is 15 bags of 50 liters.
How Do You Use the Mulch Calculator?
Pick your units
Tap Feet, inches for US sizes or Meters, cm for metric beds.
Enter bed size and depth
Type the length and width of the bed and how deep you want the mulch.
Read the bulk amount
The big number is how much mulch to order in bulk, with area and volume under it.
Count your bags
The boxes show how many 2 cu ft, 3 cu ft and 50 liter bags you need, rounded up.
Frequently Asked Questions
How many bags of mulch are in a cubic yard?
A cubic yard holds 27 cubic feet, so it equals 13.5 bags of 2 cubic feet or 9 bags of 3 cubic feet. Buy 14 of the 2 cu ft bags to cover a full yard, because you cannot buy half a bag.
How much mulch do I need for 100 square feet?
At 2 inches deep, 100 square feet needs about 16.7 cubic feet, or 0.62 cubic yards, which is 9 bags of 2 cu ft. At 3 inches deep it needs 25 cubic feet, or 0.93 cubic yards, which is 13 bags of 2 cu ft.
Should I remove old mulch before adding new?
Not usually. If the old layer has broken down and is thin, top it up to a total of 2 to 4 inches. Remove or loosen old mulch if it has matted into a crust that stops water, or if the total would go over 4 inches.
How often should mulch be replaced?
Most organic mulch breaks down within one to two years, so many gardeners top up once a year in spring. Fine mulches break down faster than coarse wood chips. Check the depth each year and add enough to bring it back to 2 to 4 inches.
Does this calculator work for rubber mulch or stone?
Yes for volume. The cubic yards and bag counts are the same whatever the material. Rubber mulch is often laid about 1.5 to 3 inches deep for beds. For stone, use a gravel calculator, which also gives the weight in tons.
How many liters are in a cubic meter of mulch?
One cubic meter is 1,000 liters, so it fills 20 bags of 50 liters or about 14 bags of 70 liters. A 4 m by 2.5 m border at 7.5 cm deep needs 0.75 m³, or 750 liters, which is 15 bags of 50 liters.
Sources and Further Reading
- University of Illinois Extension: Proper Mulching Techniques
- Iowa State University Extension: How to determine the amount of mulch needed for a garden bed
- NIST Office of Weights and Measures: Unit conversion
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Last reviewed: October 2026