Concrete Calculator
Enter the length, width and thickness of your slab to see how much concrete it takes in cubic yards and cubic feet, how many 40, 60 or 80 lb bags of mix to buy, and what ready-mix would cost by the truckload.
A 4 inch slab is standard for patios, walkways and shed floors. Driveways and garage floors usually go to 5 or 6 inches, and anything carrying a heavy vehicle or a hot tub should be 6 inches with reinforcement.
How it’s calculated
- Volume (cubic feet) = length (ft) × width (ft) × thickness (in) ÷ 12.
- Cubic yards = cubic feet ÷ 27.
- Bags = cubic feet ÷ bag yield. An 80 lb bag makes about 0.60 cu ft, a 60 lb bag 0.45 cu ft and a 40 lb bag 0.30 cu ft.
- Add 5 to 10% for spillage, uneven ground and forms that bow out. The calculator adds 10% unless you change it.
Concrete for common slab sizes
- 3×3
- 3×4
- 3×5
- 3×6
- 3×8
- 3×10
- 3×12
- 3×14
- 3×15
- 3×16
- 3×18
- 3×20
- 3×22
- 3×24
- 3×25
- 3×26
- 3×28
- 3×30
- 3×32
- 3×36
- 3×40
- 3×50
- 4×4
- 4×5
- 4×6
- 4×8
- 4×10
- 4×12
- 4×14
- 4×15
- 4×16
- 4×18
- 4×20
- 4×22
- 4×24
- 4×25
- 4×26
- 4×28
- 4×30
- 4×32
- 4×36
- 4×40
- 4×50
- 5×5
- 5×6
- 5×8
- 5×10
- 5×12
- 5×14
- 5×15
- 5×16
- 5×18
- 5×20
- 5×22
- 5×24
- 5×25
- 5×26
- 5×28
- 5×30
- 5×32
- 5×36
- 5×40
- 5×50
- 6×6
- 6×8
- 6×10
- 6×12
- 6×14
- 6×15
- 6×16
- 6×18
- 6×20
- 6×22
- 6×24
- 6×25
- 6×26
- 6×28
- 6×30
- 6×32
- 6×36
- 6×40
- 6×50
- 8×8
- 8×10
- 8×12
- 8×14
- 8×15
- 8×16
- 8×18
- 8×20
- 8×22
- 8×24
- 8×25
- 8×26
- 8×28
- 8×30
- 8×32
- 8×36
- 8×40
- 8×50
- 10×10
- 10×12
- 10×14
- 10×15
- 10×16
- 10×18
- 10×20
- 10×22
- 10×24
- 10×25
- 10×26
- 10×28
- 10×30
- 10×32
- 10×36
- 10×40
- 10×50
- 12×12
- 12×14
- 12×15
- 12×16
- 12×18
- 12×20
- 12×22
- 12×24
- 12×25
- 12×26
- 12×28
- 12×30
- 12×32
- 12×36
- 12×40
- 12×50
- 14×14
- 14×15
- 14×16
- 14×18
- 14×20
- 14×22
- 14×24
- 14×25
- 14×26
- 14×28
- 14×30
- 14×32
- 14×36
- 14×40
- 14×50
- 15×15
- 15×16
- 15×18
- 15×20
- 15×22
- 15×24
- 15×25
- 15×26
- 15×28
- 15×30
- 15×32
- 15×36
- 15×40
- 15×50
- 16×16
- 16×18
- 16×20
- 16×22
- 16×24
- 16×25
- 16×26
- 16×28
- 16×30
- 16×32
- 16×36
- 16×40
- 16×50
- 18×18
- 18×20
- 18×22
- 18×24
- 18×25
- 18×26
- 18×28
- 18×30
- 18×32
- 18×36
- 18×40
- 18×50
- 20×20
- 20×22
- 20×24
- 20×25
- 20×26
- 20×28
- 20×30
- 20×32
- 20×36
- 20×40
- 20×50
- 22×22
- 22×24
- 22×25
- 22×26
- 22×28
- 22×30
- 22×32
- 22×36
- 22×40
- 22×50
- 24×24
- 24×25
- 24×26
- 24×28
- 24×30
- 24×32
- 24×36
- 24×40
- 24×50
- 25×25
- 25×26
- 25×28
- 25×30
- 25×32
- 25×36
- 25×40
- 25×50
- 26×26
- 26×28
- 26×30
- 26×32
- 26×36
- 26×40
- 26×50
- 28×28
- 28×30
- 28×32
- 28×36
- 28×40
- 28×50
- 30×30
- 30×32
- 30×36
- 30×40
- 30×50
- 32×32
- 32×36
- 32×40
- 32×50
- 36×36
- 36×40
- 36×50
- 40×40
- 40×50
- 50×50
Questions
- How many bags of concrete are in a yard?
- A cubic yard is 27 cubic feet, so it takes 45 bags of 80 lb mix, 60 bags of 60 lb mix or 90 bags of 40 lb mix.
- Is it cheaper to buy bags or ready-mix?
- Below about 1 cubic yard, bags are usually cheaper and easier. Above 1 to 2 yards, ready-mix from a truck tends to cost less and saves hours of mixing, though many suppliers charge a short-load fee for small orders.
- How thick should a concrete slab be?
- 4 inches for patios, sidewalks and shed floors; 5 to 6 inches for driveways, garage floors and anything carrying heavy loads.
- How much does a cubic yard of concrete weigh?
- About 4,000 lb (2 tons), since normal concrete weighs roughly 145 to 150 lb per cubic foot.