Concrete Calculator
Calculate how much concrete (cubic yards and bags) you need for a slab.
What is the Concrete Calculator?
This tool calculates the volume of concrete needed for a slab from its length, width and thickness, and converts that into the number of pre-mixed concrete bags required, using each bag size's published yield.
The formula
Cubic Feet = Length × Width × (Thickness ÷ 12). Cubic Yards = Cubic Feet ÷ 27. Bag yields follow the standard published rates (consistent across major brands like Quikrete and Sakrete, per ASTM C387): an 80lb bag yields about 0.6 cubic feet, scaling down proportionally for 60lb (0.45 cu ft), 50lb (0.375 cu ft) and 40lb (0.3 cu ft) bags.
How to use it
- Enter your slab's length, width and thickness.
- Choose the bag size you plan to buy.
- Buy slightly more than the calculated number of bags to account for spillage and an uneven subgrade.
Want the "why" behind this tool? Read Why Concrete Bags Are Sold by Weight but You Need to Think in Volume.