Concrete calculator
Enter the size and thickness of your slab. You get cubic yards for a truck delivery and bag counts for smaller pours.
Figures last reviewed October 2026. See sources.
Slab thickness: typical ranges
These are common ranges, not requirements. Your soil, climate, and local rules may call for something different.
| Use | Depth |
|---|---|
| Walkways and patios | About 4 in |
| Driveways | 4 to 6 in |
How this is calculated
Area times thickness gives volume in cubic feet. Divide by 27 for cubic yards. Bag counts divide the volume by the yield of one bag and round up.
Bag yields differ by brand and size. This calculator uses the yields on a major manufacturer's data sheet: about 0.6 cubic feet for an 80 lb bag, 0.45 for 60 lb, 0.375 for 50 lb, and 0.3 for 40 lb. Check the yield printed on your bag. Footings, thickened edges, and reinforcement are not included. For a round column or footing, choose Circle, enter the diameter, and enter the height as the thickness.
Example: a 10 ft by 10 ft area at 4 inches deep, with 10% extra, needs about 1.36 cubic yards (36.7 cubic feet), or 62 80 lb bags or 82 60 lb bags.
How far does one cubic yard go?
Area covered by one cubic yard at different depths, before any extra material.
| Depth | Square feet covered |
|---|---|
| 4 in | 81 |
| 5 in | 65 |
| 6 in | 54 |
Quick reference: common sizes
Amount needed in cubic yards, including the default 10% extra. Use the calculator above for your exact size.
| Area | 4 in deep | 6 in deep |
|---|---|---|
| 10 × 10 ft | 1.36 | 2.04 |
| 10 × 12 ft | 1.63 | 2.44 |
| 12 × 12 ft | 1.96 | 2.93 |
| 20 × 20 ft | 5.43 | 8.15 |
| 12 × 24 ft | 3.91 | 5.87 |
Common questions
How much concrete do I need?
Multiply the area in square feet by the thickness in feet to get cubic feet, then divide by 27 for cubic yards. A 10 by 10 foot slab that is 4 inches thick is about 1.23 cubic yards before any allowance for waste.
How many bags of concrete are in a cubic yard?
A cubic yard is 27 cubic feet, which is about 45 bags at 0.6 cubic feet each (80 lb), 60 bags at 0.45 (60 lb), 72 bags at 0.375 (50 lb), or 90 bags at 0.3 (40 lb). Always check the yield on your bag.
Should I add extra?
Most people add an allowance for spillage, uneven ground, and over-excavation. The default is 10%. You can change it under the advanced options.
How thick should a concrete slab be?
Patios and walkways are commonly 4 inches thick, and driveways 4 to 6 inches. Thickness depends on the load and local conditions, so confirm with a contractor or local requirements.
Does this include footings or rebar?
No. This estimates a simple flat slab. Footings, thickened edges, and other structural elements need their own calculation and should follow local building rules.
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