Concrete Calculator
Work out the volume of concrete for a slab, footing or column, and how many premix bags or cubic yards to order.
How to use the Concrete Calculator
- Choose the pour shape.
- Enter the length and pick its unit.
- Enter the width and pick its unit.
- Enter the diameter and pick its unit.
- Enter the thickness / depth and pick its unit.
- Enter the quantity.
- Enter the extra for waste.
- Enter the price per cubic yard.
- Press Calculate. The result updates automatically as you type, and you can switch the result unit at any time.
About the Concrete Calculator
Ordering the right amount of concrete avoids a costly second delivery or a pile of leftover mix. Measure the form in feet and the thickness in inches, add 5–10% for spillage and uneven sub-grade, and round up.
For pours under about one cubic yard, premixed bags are usually cheaper. For larger slabs, order ready-mix by the cubic yard (or cubic meter).
Formula
Slab volume = Length × Width × Thickness
Round volume = π × (Diameter ÷ 2)² × Depth
Cubic yards = cubic feet ÷ 27
Bag counts use typical premix yields: a 40 lb bag makes about 0.30 ft³, a 60 lb bag about 0.45 ft³ and an 80 lb bag about 0.60 ft³ of concrete.
Example calculation
Using the default values:
- Pour shape = Slab / footing (rectangular)
- Length = 10 ft
- Width = 10 ft
- Thickness / depth = 4 in
- Quantity = 1
- Extra for waste = 10%
the calculator returns:
- Concrete needed: 1.358 yd³
- 40 lb bags: 123 bags
- 60 lb bags: 82 bags
- 80 lb bags: 62 bags
Frequently asked questions
How many bags of concrete make a cubic yard?
About 45 bags of 80 lb, 60 bags of 60 lb, or 90 bags of 40 lb premix make one cubic yard (27 ft³).
How thick should a concrete slab be?
Patios and walkways are usually 4 inches thick. Driveways are commonly 4–6 inches, and garage floors that carry heavy loads 5–6 inches.
How much does a yard of concrete weigh?
Normal concrete weighs about 4,000 lb (around 1.8 metric tons) per cubic yard.
Last updated: · Category: Construction calculators