Concrete calculator
Measurements
What you need
Quantity · Amount- 01Slab volume10 × 10 ft × 4 in33.3 cu ft
- 02Concrete to order, 10 % extra36.7 cu ft1.36 cu yd
- 03Weight, cured150 lb per cu ft2.76 tons
- 04Ready-mix$160 per cu yd, ordered by the quarter yard1.5 cu yd$240
- 0580 lb bags0.6 cu ft per bag (manufacturer yield) at $862 bags$465
- 62 bags is a lot of mixing; a ready-mix truck would be about $217.
- Order ready-mix by the quarter yard, rounded up; the truck cannot deliver a fraction of what you order back.
The material
Prices — put in what you were quoted
Where these figures come from
- Bag yields from the manufacturer's tables: 80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45, 50 lb ≈ 0.375, 40 lb ≈ 0.30.
- Normal-weight concrete ≈ 150 lb per cu ft.
- Prices are typical US figures at the date on this sheet; ready-mix quotes vary by mix design and distance.
Pick the shape, type the dimensions, and the sheet gives cubic yards with a 10 % allowance for uneven ground and spillage, the number of bags at the yields printed on the bag (an 80 lb bag makes 0.60 cu ft), and what it costs bagged or as ready-mix delivered by truck. Above about a yard, ready-mix is usually cheaper and much less work.
Worked examples
- Patio slab 12 × 12 ft, 4 in thick
- 1.96 cu yd — concrete to order, 10 % extra, about $668 in bagged.
- Shed pad 8 × 10 ft, 4 in, bagged
- 1.09 cu yd — concrete to order, 10 % extra, about $368 in bagged.
- Six 12 in × 3 ft footings
- 0.58 cu yd — concrete to order, 10 % extra, about $195 in bagged.
- Driveway 12 × 40 ft, 5 in, ready-mix
- 8.15 cu yd — concrete to order, 10 % extra, about $1,320 in ready-mix.
How it is worked out
Slab: length × width × thickness (ft) = cubic feet. Column: π × (diameter ÷ 2)² × height. Multiply by the count, add the allowance, divide by 27 for cubic yards. Bags = cubic feet ÷ the yield per bag (80 lb 0.60, 60 lb 0.45, 50 lb 0.375, 40 lb 0.30 cu ft), rounded up. Ready-mix is rounded up to the quarter yard.
The figures behind it
- Bag yields from the manufacturer's tables: 80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45, 50 lb ≈ 0.375, 40 lb ≈ 0.30.
- Normal-weight concrete ≈ 150 lb per cu ft.
- Prices are typical US figures at the date on this sheet; ready-mix quotes vary by mix design and distance.
Every figure here is an estimate. Materials vary with moisture, compaction and product; order a little extra and confirm quantities with your supplier.
Questions people ask
- How many 80 lb bags of concrete make a cubic yard?
- 45. An 80 lb bag yields 0.60 cu ft and a cubic yard is 27 cu ft. A 60 lb bag yields 0.45 cu ft, so 60 bags; a 40 lb bag yields 0.30 cu ft, so 90 bags.
- How much concrete for a 10 × 10 slab?
- At 4 inches thick, 33.3 cu ft, or 1.23 cu yd; with 10 % extra, 1.36 cu yd, which is 62 bags of 80 lb or a ready-mix order of 1.5 cu yd.
- Bags or a truck?
- Up to about half a cubic yard (23 bags of 80 lb), bags and a mixer are practical. Above a yard, a ready-mix truck is cheaper per yard and the whole pour cures as one piece, but plants charge short-load fees below their minimum, often 5–10 yards.
- How thick should a slab be?
- Four inches for patios, walkways and sheds; five to six for driveways and garage floors; footings follow the local code, commonly 8–12 in deep and twice the wall width.
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