Concrete Calculator
Calculate how much concrete you need for a slab, footing, or post hole — in cubic yards, cubic meters, or bags.
A flat slab, like a patio, shed base, or driveway.
Extra material to cover cuts, mistakes, and offcuts.
Bags
880
Ready-mix
11 m³
delivered
💡 For a project this size, ready-mix delivery is probably more practical than bagged concrete.
How this is calculated
Volume = length × width × depth, then increased by your waste allowance.
Bag counts are rounded up to the nearest whole bag, based on standard manufacturer yield ratings for the selected bag size. The ready-mix vs. bags suggestion is a rough guideline, not a rule — check delivery minimums with your local supplier.
Results are estimates. Verify measurements and local requirements before purchasing materials or beginning construction.
How to measure for concrete
Measure the length and width of the area you're pouring, and decide on a depth — 4 inches (10 cm) is standard for a patio or shed slab; footings and post holes are usually deeper. For round holes and footings, measure the diameter instead of length and width.
Add a waste allowance to cover uneven ground, spillage, and formwork loss — 10% is a reasonable default for most DIY pours.
Frequently asked questions
How much concrete do I need for a slab?
Multiply the slab's length, width, and depth to get volume. This calculator does that for you and adds a waste allowance to cover uneven ground, spillage, and formwork loss.
How many bags of concrete do I need?
Bag counts depend on the bag size. A standard 80 lb bag yields about 0.022 cubic yards (0.0168 m³) of mixed concrete; a 60 lb bag yields about 0.017 cubic yards, and a 25 kg bag (common outside the US) yields about 0.0125 m³. Choose your bag size above to see the count.
Should I order ready-mix or use bags?
For pours larger than about 1 cubic yard (0.75 m³), ready-mix delivery is usually more practical and often cheaper per unit volume than bagged concrete. Use the cubic yard/meter result when getting a ready-mix quote.
How much waste allowance should I use?
10% is a reasonable default for most DIY pours. Increase it for uneven or unformed ground, irregular shapes, or if you're new to pouring concrete.