Ordering concrete to the exact yard and coming up short

Say the patio is 20 by 20 and the plan is 4 inches thick. 400 square feet times a third of a foot is 133 cubic feet. Divide by 27 and the forms hold 4.94 yards.

So you order 5. It looks like it covers it with a little to spare.

Then the truck backs up, the chute swings over, and the last corner doesn't fill. Say the subgrade came out half an inch low across the whole patio. That's 400 square feet at 4.5 inches, which is 150 cubic feet, or 5.56 yards. You ordered 5. You're more than half a yard short, with most of a slab already down.

Now you're calling the plant for a second truck. Say a short load fee and a second delivery run you $300 between them, and your crew stands around for an hour waiting on it. Say a yard of concrete costs you $160. The extra yard you didn't order would have cost $160, a little over half what the second truck did, before you count the hour.

Order for the trip you can't afford to make twice

The math gives you what the forms hold if everything goes right. Subgrade runs a little low and some spills off the chute, and none of that shows up in length times width times depth.

Kevin Goodwin, a contractor in Alabama who helped build Yardstick, orders half a yard over, and his plant only sells whole yards. On this patio that's 4.94 plus a half, 5.44, so six yards on the ticket. Six covers the 5.56 the low subgrade needed, with 0.44 to spare.

It's the same reason he adds a whole yard to every mulch order: one extra unit is cheap, and the second trip isn't. Put that extra in your price, too. It belongs on the estimate the same way the forms around the slab do, because you pay for it either way.

Yardstick adds the extra you always order, then rounds up to what your plant sells.