Use this free concrete calculator to estimate how many cubic yards or cubic feet of concrete you need for a slab, footing, or column. Enter your dimensions to get an instant volume estimate plus the number of 60-lb and 80-lb bags needed if mixing by hand.
How to use this Concrete Calculator
1. Select your shape using the tabs — Slab/Patio for flat surfaces, Footing for rectangular footings, and Column for round tube forms.
2. Enter your dimensions. For slabs, thickness is entered in inches. For footings, all measurements are in feet. For columns, diameter and height are in inches.
3. Click Calculate Concrete to see the cubic yards and cubic feet needed, plus the number of pre-mix bags required if you are mixing by hand.
4. The result already includes a 10% waste allowance. When ordering ready-mix concrete, give the supplier the cubic yard number shown.
Frequently asked questions
How much does a yard of concrete cover?
One cubic yard of concrete covers 81 square feet at 4 inches thick, 54 square feet at 6 inches thick, or 27 square feet at 12 inches thick. A standard residential driveway or patio is typically poured at 4 inches, while driveways that will support heavy vehicles should be 6 inches thick.
When should I order ready-mix instead of using bags?
For any pour larger than about 1 cubic yard (27 cubic feet), ordering ready-mix concrete from a supplier is more economical and practical than mixing bags by hand. Ready-mix ensures a consistent mix ratio, saves significant labor, and can be poured faster. Pre-mix bags are best suited for small projects like fence posts, steps, and repairs.
What is the standard concrete mix ratio?
The most common mix for residential slabs is 1 part cement, 2 parts sand, and 3 parts gravel, with a water-to-cement ratio of about 0.45 to 0.50. Pre-mix bags come with the dry ingredients already proportioned — you just add water. For structural applications, consult a structural engineer for the appropriate mix design.
How long does concrete take to cure?
Concrete reaches about 70% of its strength in 7 days and full design strength at 28 days. You can walk on a slab after 24 to 48 hours, drive on it after 7 days, and expect full strength at 28 days. Keep the surface moist for the first 7 days by misting or covering with plastic to prevent cracking from rapid moisture loss.
Do I need a permit to pour a concrete slab?
Permit requirements vary by municipality and project size. Many jurisdictions require permits for slabs larger than 200 square feet, any structure attached to the house, or work in setback areas. Check with your local building department before starting any concrete project larger than a small patio or walkway.