Concrete Calculator
Calculate how much concrete you need for a slab, patio, or footing. Enter the dimensions to get the volume in cubic yards and cubic feet, plus the number of 60 lb and 80 lb bags required.
Formula reviewed for accuracy. Our methodology & sources
Concrete Calculator
construction calculator
How It Works
The calculator converts the slab thickness from inches to feet, multiplies it by the length and width to get the volume in cubic feet, then divides by 27 to express it in cubic yards — the unit ready-mix concrete is ordered in. It also divides the volume by the yield of a 60 lb and an 80 lb bag to estimate how many bags a small pour would take. It is wise to add about 5–10% to the result to cover spillage and uneven subgrade.
Formula
Cubic Feet = Length × Width × (Thickness ÷ 12) Cubic Yards = Cubic Feet ÷ 27
Examples
10×10 ft slab, 4 in thick
1.23 cubic yards, about 74 bags of 60 lb.
Frequently Asked Questions
How much concrete do I need?
Multiply length × width × thickness (in feet), then divide by 27 for cubic yards. A 10×10 ft slab at 4 inches thick needs about 1.23 cubic yards.
How many bags of concrete in a cubic yard?
A cubic yard requires about 60 bags of 60 lb concrete or 45 bags of 80 lb concrete. For large pours, ready-mix delivery is usually more economical.