partners@corneliacove.com
Talk to us

Free tool · No sign-up

Concrete calculator: cubic yards and bags for a slab

The short answer

Multiply length by width by thickness in feet, then divide by 27 to get cubic yards. A 20 by 10 foot slab, 4 inches thick, is 2.47 cubic yards before waste, or 2.59 with 5% extra. In bags, that’s 117 of the 80 lb size, since Quikrete lists one at about 0.60 cubic feet.

Enter the slab’s length, width and thickness to get cubic yards and bags. Then add your costs and labor if you’re quoting the job.

The slab or pad

10 feet 6 inches is 10.5.
Covers uneven ground and spillage.

Price the job (optional)

An example. Use your supplier’s price.
What you charge for an hour, not what you pay.

Concrete you need

2.59 cubic yards

70 cubic feet of concrete, covering 200 square feet.

80 lb bags (0.60 cubic feet each)
117
60 lb bags (0.45 cubic feet each)
156
40 lb bags (0.30 cubic feet each)
234

Price for this job

Materials (2.59 × $180.00)
$466.67
Labor
$0.00
Markup
$93.33
Price to quote
$560.00

How it works

The formula

Cubic yards = length (ft) × width (ft) × thickness (in) ÷ 12 ÷ 27. Add some extra, because forms bow and ground is rarely perfectly flat.

Bags for one cubic yard (27 cubic feet)
Bag sizeYield per bagBags per cubic yard
40 lb0.30 cu ft90
60 lb0.45 cu ft60
80 lb0.60 cu ft45

Bag yields are from Quikrete’s data sheet for its Concrete Mix (opens in a new tab). Other mixes and brands can differ, so check the bag.

Bags or a truck?

Compare your supplier’s price for a delivered yard, including any short-load fee, against the bags plus the mixing time. Ask about their minimum order before you decide.

When the numbers look right, put them on an estimate. The markup and margin calculator shows what your markup leaves as profit.

Common questions

How do I calculate concrete in cubic yards?
Multiply length by width by thickness, all in feet, and divide by 27. Thickness in inches gets divided by 12 first. A 10 by 10 foot slab at 4 inches is 10 × 10 × 0.333 ÷ 27, or 1.23 cubic yards.
How many 80 lb bags of concrete are in a yard?
45, going by Quikrete’s listed yield of about 0.60 cubic feet per 80 lb bag. A cubic yard is 27 cubic feet, and 27 ÷ 0.60 is 45.
How much extra concrete should I order?
This calculator starts at 5%. Rough or uneven ground takes more, so add more if your base isn’t level. Change the number to match how your jobs usually go.
Can I use this for footings or round columns?
For a square footing, yes: use its length, width and depth. A round column needs the circle’s area instead. Work that out in square feet, then use the cubic yard calculator.
How do I price a concrete job?
Add your material cost and your labor, then add your markup. The calculator’s pricing panel does this once you enter your supplier’s price, the labor hours and your rate.

More free tools

See all free tools

Busy measuring? Your phone can still get answered

CoveDesk answers your business calls while you’re on a job and texts you who called and what they need.

Talk to usSee pricing