Mulch calculator — how much mulch do I need?

The short answer

One cubic yard of mulch covers 162 square feet at 2 inches, or 108 square feet at 3 inches. Divide your bed area by that number and you have your yards. Everything below is why those numbers are what they are, and what else moves the order.

How the math works

A cubic yard is 27 cubic feet. Depth in inches divided by 12 turns your depth into feet, so:

• Cubic yards = area (sq ft) × depth (in) ÷ 12 ÷ 27
• Coverage = 27 ÷ (depth ÷ 12) square feet per yard — 324 at 1", 162 at 2", 108 at 3", 81 at 4"
• Bags = yards × 27 ÷ bag size, rounded up. At 2 cubic feet a bag that is 13.5 bags to the yard.

The tool then adds a 10% order buffer, which is the figure Estima itself adds on a real estimate. Beds are not flat, bags do not empty cleanly, and a wheelbarrow spills. Ten percent is the difference between finishing the bed and going back to the yard.

Two inches or three?

Two inches is a refresh — a bed that already has mulch in it and needs its color and depth brought back. That is most spring visits on a maintenance route, and it is the default here because it is the job that comes up most.

Three inches is a new bed from bare soil. Three is what suppresses weeds and holds moisture through a dry August, and going deeper is not better: past about four inches you start starving roots of air and creating a mat that sheds water instead of letting it through.

The difference matters more than it sounds. The same 280 square foot bed is 1.73 yards at two inches and 2.59 at three — a 50% swing on one dropdown.

Bags or bulk?

Bulk is measured in yards and dumped; bagged is 2 or 3 cubic feet at a time, and it takes 13.5 two-cubic-foot bags to make a yard. Anything over a yard or so is generally worth taking in bulk if you have somewhere to put it and a way to move it. Under that, bags win on convenience — no minimum, no delivery window, and no pile on the driveway when it rains.

The break-even depends on your yard's pricing and their delivery minimum, which is why this page does not try to tell you which is cheaper. Ask them for both numbers once and you will know for the season.

Types, briefly

Shredded hardwood knits together and stays put on a slope. Bark nuggets last longer but float, so keep them off anywhere that drains hard. Dyed mulches hold color through the season and fade slower than natural, which is why they show up on commercial properties. Compost blends feed the bed but break down faster, so plan on topping them up sooner.

Whatever you use, keep it off the trunks. A cone of mulch piled against bark holds moisture against it, invites rot and rodents, and kills trees slowly enough that nobody connects the two. Pull it back a couple of inches and leave the flare showing.

A worked example

A 20 × 14 bed — 280 square feet — refreshed at two inches:

• Straight volume: 280 × (2 ÷ 12) ÷ 27 = 1.73 cubic yards
• With the 10% buffer: 1.90 cubic yards — order two
• Bagged instead: 1.90 × 27 ÷ 2 = 26 bags

That last line is the argument for bulk on anything this size. Twenty-six bags is most of a pickup bed and an afternoon of opening them.

Questions we get

How many square feet does a yard of mulch cover?

162 at two inches deep, 108 at three, 81 at four. The tool shows this for whatever depth you enter.

How many bags in a cubic yard?

13.5 bags at 2 cubic feet each, or 9 bags at 3 cubic feet.

How much mulch for a 1,000 square foot bed?

6.17 cubic yards at two inches, 9.26 at three — before the order buffer.

Should I remove the old mulch first?

Usually not. Break up any crust, pull it back off the crowns and trunks, and top it up. Strip it only when the bed has built up past three or four inches, or when it has matted into a layer water runs off.

When should I mulch?

Spring, once the soil has warmed — mulching over cold ground keeps it cold. A lighter autumn top-up is fine where you want winter protection.

Does the buffer double-count if I round up to whole yards anyway?

A little, and that is deliberate. Set the buffer to zero if you would rather do the rounding yourself.