How Many Bags of Concrete for a Slab? 80 lb and 60 lb Chart

There's one table for 4 inch slabs and one for 6 inch slabs. Each row gives the bag count for 80 lb and 60 lb bags. The last column is cubic yards, for when you'd rather order ready-mix.

4 inch slab

Bags of concrete for a 4 inch slab, with 10% waste
Slab	80 lb bags	60 lb bags	Cubic yards
4 × 4 ft	10	14	0.22
6 × 6 ft	22	30	0.49
8 × 8 ft	40	53	0.87
10 × 10 ft	62	82	1.36
10 × 12 ft	74	98	1.63
12 × 12 ft	88	118	1.96
12 × 16 ft	118	157	2.61

6 inch slab

Bags of concrete for a 6 inch slab, with 10% waste
Slab	80 lb bags	60 lb bags	Cubic yards
4 × 4 ft	15	20	0.33
6 × 6 ft	33	44	0.73
8 × 8 ft	59	79	1.30
10 × 10 ft	92	123	2.04
10 × 12 ft	110	147	2.44
12 × 12 ft	132	176	2.93
12 × 16 ft	176	235	3.91

How this is worked out

Length times width times thickness gives the volume in cubic feet. We add 10% for waste, which is Handyman Calc's default.

An 80 lb bag makes 0.60 cubic feet of concrete. A 60 lb bag makes 0.45. Those are the yields the app uses. We divide by the yield and round up, since you can't buy part of a bag.

The cubic yards column is the same volume with waste, divided by 27. Use it if you're ordering ready-mix.

The math is done in exact fractions. So a row that comes out to a whole number of bags stays that number. It isn't pushed up one by a rounding error.

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Slab not on the list? Handyman Calc works out any size. It does footings and round piers too. Try Handyman Calc free in your browser. There's nothing to install and no account.

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There's a chart for how many sheets of drywall for a room too, and more on the Handyman Calc page.