Mulch math: what a cubic yard actually covers

Most mulch bids are never checked, because most property managers were never handed the one formula that checks them. Here it is, with the numbers worked through, so the next bid that crosses your desk takes five minutes to sanity-check instead of a leap of faith.

The only number you need: 27

A cubic yard is 27 cubic feet. Spread it across a bed and the coverage depends entirely on depth. That is the whole trick, and it is just division:

• At 2 inches deep: one cubic yard covers about 162 square feet.
• At 3 inches deep: one cubic yard covers about 108 square feet.
• At 4 inches deep: one cubic yard covers about 81 square feet.

So the working formula is: square feet of bed, divided by the coverage for your depth, equals cubic yards. A property with 10,000 square feet of beds at a three-inch spec needs about 93 yards. At two inches it needs about 62. That gap, one inch of depth, is a third of the material and a third of the material cost. Keep that in mind for the next section.

Why two bids for the same property can be 40% apart

When two quotes for the same beds land far apart, one of four things is going on, and only one of them is a bargain:

• Different depth assumptions. One bid priced three inches, the other priced two and did not say so. On day one they look identical. By August the thin install has bare patches and weeds.
• Different measurements. One contractor measured the beds, the other eyeballed from the truck. Eyeballed area is usually generous, and you pay for the generosity.
• Different material. Grades of mulch vary widely in cost, longevity, and how they look in month nine. A line item that just says "mulch" is hiding the most important word.
• Different efficiency. Labor is the other half of an install. A crew hand-spreading from a pile prices differently than material placed by air directly into the beds. Same yards, very different day.

How to sanity-check any bid in five minutes

Ask every bidder for three numbers, in writing: total square feet, spec depth, and cubic yards. Then run the formula yourself. If the yardage does not follow from the area and the depth, somebody measured wrong or plans to spread thin, and either way you have learned something worth knowing before you sign. A bidder who will not commit to those three numbers has answered a different question for you.

And insist the depth is in the contract. "Refresh the beds" is not a spec. "Three inches maintained across 10,400 square feet" is a spec, and it is checkable with a ruler.

Where we land on this

Our commercial mulch installation quotes are fixed and itemized: measured area, spec depth, material grade, yardage you can re-run through the formula above. Material is placed by air, evenly and to depth across the whole bed, so the inches you bought are the inches on the ground in the back corner, not just along the curb where everyone looks.

Mulch is one of the few line items on a property where you can audit the entire bid with grade-school math. Use it. The good contractors will not mind, and the other kind will mind very much, which is also useful information.