How Much Mulch Do I Need?

How do you calculate how much mulch you need?

Multiply square feet by depth in inches and divide by 324; the result is cubic yards. The number 324 comes from unit conversion: 12 inches in a foot times 27 cubic feet in a cubic yard. Put another way, one cubic yard spread 1 inch deep covers exactly 324 square feet.

To measure area, multiply length by width for a rectangle. Break an irregular bed into rectangles and add them, or see how to calculate square footage for circles and triangles. The mulch calculator takes a total area or a list of beds and gives cubic yards, cubic feet, liters and bag counts.

How much mulch for a typical garden bed? A worked example

Take two beds, one 20 by 10 feet and one 12 by 4 feet, mulched 3 inches deep. The areas are 200 and 48 square feet, for a total of 248 square feet. Then 248 × 3 ÷ 324 = 2.30 cubic yards, or 62 cubic feet (2.30 × 27).

Our mulch calculator returns 31 bags of 2 cubic feet (62 ÷ 2) or 21 bags of 3 cubic feet (62 ÷ 3 = 20.67, rounded up). At an illustrative $4.50 per 2-cubic-foot bag, 31 bags cost $139.50; actual prices vary by store and material, so use the price box in the calculator with your local figure.

If the beds still have an inch of old mulch in good condition, count only the depth you are adding. Topping up 2 inches on the same 248 square feet needs 248 × 2 ÷ 324 = 1.53 cubic yards instead of 2.30.

How much does a cubic yard of mulch cover?

A cubic yard of mulch covers 324 square feet at 1 inch, 162 at 2 inches, 108 at 3 inches and 81 at 4 inches. Divide 324 by the depth in inches to get the coverage at any depth.

A cubic yard is 27 cubic feet, the volume of a cube 3 feet on each side. If you plan to haul it yourself, ask the supplier how much a yard of that material weighs and check it against your vehicle's payload rating, since wet mulch is heavy.

How many bags of mulch do you need?

Divide the cubic feet of mulch by the bag size and round up. One cubic yard (27 cubic feet) is 13.5 bags of 2 cubic feet, so 14 in practice, or exactly 9 bags of 3 cubic feet. The chart below shows our mulch calculator's results, rounded up to whole bags.

How deep should mulch be?

Aim for 2 to 4 inches for most beds and around trees and shrubs. University of Illinois Extension recommends 2 to 4 inches overall, with composted material at 2 to 3 inches and coarse mulch at 3 to 4 inches, because thick layers can mat down and reduce water and oxygen reaching the roots. University of Florida's Florida-Friendly Landscaping program recommends 3 inches. Mississippi State University Extension's gardening column considers 2 to 3 inches sufficient for most uses.

Small plants need less. The University of Florida suggests only 1 inch around seedlings and small vegetables or herbs so growth isn't inhibited. Around trees, Illinois Extension advises keeping mulch at least 4 inches away from the trunk rather than piling it against the bark.

Should you buy mulch in bags or in bulk?

Bags are usually simpler for small jobs, and bulk delivery usually makes sense as the job grows, so compare the two on the same unit. Multiply the bag price by 13.5 for 2-cubic-foot bags or by 9 for 3-cubic-foot bags to get a price per cubic yard, then compare it with the supplier's bulk price plus any delivery fee.

Bags are easier to move with a small vehicle and keep clean until you use them. Bulk mulch needs a place to dump the pile and a wheelbarrow to move it. Whichever you choose, round up slightly: a small surplus is easy to use elsewhere, while running short means another trip.

How do you calculate gravel and concrete with the same formula?

Gravel and concrete use the same volume math: area in square feet × depth in inches ÷ 324 gives cubic yards. What changes is how you buy them. Gravel is often sold by weight, and concrete is ordered by the yard or bought in premixed bags.

Gravel example: a 200-square-foot path 3 inches deep needs 200 × 3 ÷ 324 = 1.85 cubic yards. The gravel calculator, at its default density of 1,600 kg per cubic meter (about 100 pounds per cubic foot), puts that at 2.5 short tons. Density varies by stone, and the calculator suggests adding 5 to 10% for a compacted base.

Concrete example: a 10 by 10 foot slab 4 inches thick has 100 × 4 ÷ 324 = 1.23 cubic yards. The concrete calculator converts that to 56 bags of 80-pound premix (about 0.60 cubic feet each) or 75 bags of 60-pound premix (about 0.45 cubic feet each), before the 5 to 10% extra it recommends for spillage and uneven ground. At that size most people compare the bag cost and labor with a ready-mix delivery.