Concrete Calculator
Work out exactly how much concrete your project needs — in cubic yards, bags, and dollars — for slabs, footings, columns, and stairs.
Results are estimates for planning only. Concrete volume can vary with subgrade, formwork, and finishing. Always order a 5–10% overage and confirm against your supplier's quote and local building code.
How to Measure for Concrete
Accurate measurements are the difference between one clean pour and an awkward second delivery. Measure to the inside face of your forms, and keep length and width in feet but depth or thickness in inches — the calculator handles the conversion.
Slabs & patios
Measure the length and width of the formed area in feet. For thickness, use the finished depth of concrete: 4" for patios and walkways, 5–6" for driveways. If the slab is L-shaped, split it into rectangles and add the results.
Footings
Enter the total trench length in feet, then the footing width and depth in inches. For a continuous footing around a building, use the full perimeter length.
Round columns & piers
Measure the tube or form diameter in inches and the pour height in feet. Set the quantity to pour several identical columns at once.
Stairs
Count the steps, then measure the rise (height of one step) and run (tread depth) in inches, plus the stair width in feet. The calculator treats the steps as solid concrete.
Common Mistakes to Avoid
- Forgetting the waste allowance. Subgrade is never perfectly level. Skipping the 5–10% overage is the number one reason pours run short.
- Mixing up feet and inches for thickness. Entering "4" as feet instead of inches overestimates volume 12×. Thickness is in inches.
- Measuring outside the forms. Concrete fills the space inside the formwork — measure there, not the outer edge of the lumber.
- Buying bags for a big pour. Anything over ~1 cubic yard is cheaper and far easier as truck-delivered ready-mix.
- Ignoring slope and over-dig. Trenches and footings are almost always slightly deeper than planned — round up, never down.
Frequently Asked Questions
A 10 ft × 10 ft slab poured 4 inches thick is 33.3 cubic feet, or about 1.23 cubic yards. Add 10% waste and you should order roughly 1.4 cubic yards of ready-mix concrete.
An 80 lb bag of pre-mix concrete yields about 0.60 cubic feet. A cubic yard is 27 cubic feet, so you need about 45 bags of 80 lb concrete per cubic yard (60 bags of 60 lb, or 90 bags of 40 lb).
Yes. Always add a 5–10% waste allowance for spillage, uneven subgrade, and over-excavation. Running short mid-pour creates a cold joint or a costly second delivery, so ordering slightly extra is cheap insurance.
Four inches is standard for patios, walkways, and shed floors. Use 5–6 inches for driveways or anything that carries vehicle weight. Always confirm with your local building code.
Bagged pre-mix suits small jobs under about half a cubic yard. Beyond roughly 1 cubic yard, ready-mix delivered by truck is usually cheaper and far less labor than mixing dozens of bags by hand.