Concrete Calculator
Estimate how much concrete you need for slabs, footings, columns, stairs, and other projects. Get cubic yards, pre-mix bags, and an optional cost estimate.
Results
- Concrete needed
- 1.23 cu yd
- With 10% waste
- 1.36 cu yd
- Cubic feet
- 33.33 cu ft
- Cubic meters
- 0.94 m³
- 80 lb bags
- 62 bags
- 60 lb bags
- 82 bags
- 40 lb bags
- 123 bags
Estimates only. Round up and buy a little extra to account for waste, spills, and breakage.
Pouring a slab, footing, set of stairs, or column? This concrete calculator tells you exactly how much concrete you need in cubic yards, plus the number of 40, 60, and 80 lb pre-mix bags so you can decide between bags and a ready-mix truck.
It is built for real pours, not textbook math: choose your shape, set a thickness, and add a waste factor for uneven subgrade so you do not run short mid-pour and end up with a cold joint.
Also works as a concrete slab calculator, concrete bag calculator, cement calculator, concrete yardage estimator, and Quikrete bag calculator.
How to use the concrete calculator
- Enter the shape.
- Enter the length in ft.
- Enter the width in ft.
- Enter the thickness in in.
- Enter the waste factor in %.
- Optionally add a price to estimate the total project cost.
- Read your quantities instantly — no sign-up, and you can print the estimate to take to the supplier.
Worked example
Inputs
- Shape
- Rectangle / Square
- Length
- 10 ft
- Width
- 10 ft
- Thickness
- 4 in
- Waste factor
- 10 %
Results
- Concrete needed
- 1.23 cu yd
- With 10% waste
- 1.36 cu yd
- Cubic feet
- 33.33 cu ft
- Cubic meters
- 0.94 m³
- 80 lb bags
- 62 bags
- 60 lb bags
- 82 bags
- 40 lb bags
- 123 bags
Using the example values above, the concrete calculator returns 1.23 cu yd (concrete needed). Change any field to match your own project and the numbers update instantly.
How much concrete do I need for a slab?
Concrete is ordered by the cubic yard (27 cubic feet). To find yards, multiply length × width × thickness in feet, then divide by 27. A 10 ft × 10 ft slab at 4 inches thick works out to about 1.23 cubic yards before waste.
For anything under roughly half a yard, bags are usually cheaper and more practical. Above that, a ready-mix truck almost always wins on price and time — most suppliers have a 1-yard minimum and short-load fees.
Bags vs. ready-mix
One cubic yard takes about 45 bags of 80 lb, 60 bags of 60 lb, or 90 bags of 40 lb mix. Mixing more than ~20 bags by hand is hard work, so use the bag counts above to sanity-check whether ordering a truck makes more sense.
How much extra should I order?
Always order a little extra. A 5% waste factor suits simple, square projects; 10% is right for most jobs; bump it to 15–20% for irregular shapes, diagonal patterns, or uneven ground. Running short almost always costs more than the leftover material.
Concrete bag yields
| Bag size | Yield (cu ft) | Bags per cu yd |
|---|---|---|
| 40 lb | 0.30 | 90 |
| 50 lb | 0.375 | 72 |
| 60 lb | 0.45 | 60 |
| 80 lb | 0.60 | 45 |
Formula
Volume (cu ft) = area × thickness ÷ 12. Cubic yards = cu ft ÷ 27. Bags ≈ cu ft ÷ yield per bag.
Frequently asked questions
- How many bags of concrete are in a cubic yard?
- About 45 bags of 80 lb, 60 bags of 60 lb, or 90 bags of 40 lb pre-mix concrete equal one cubic yard.
- How much extra concrete should I order?
- Order 5–10% extra for spillage and uneven subgrade. For complex pours, add up to 15%.
- How do I calculate cubic yards of concrete?
- Multiply length × width × thickness in feet, then divide by 27. For thickness in inches, divide the inches by 12 first.
- How much is a yard of concrete?
- Ready-mix concrete typically runs $125–$170 per cubic yard delivered, before short-load or Saturday fees. Enter a local price to estimate your total.
- How much concrete does an 80 lb bag of Quikrete make?
- An 80 lb bag yields about 0.6 cubic feet, so it takes roughly 45 bags to fill one cubic yard.
Related calculators
Concrete Slab Calculator
Estimate cubic yards and bags of concrete for a rectangular slab.
Concrete Footing Calculator
Estimate cubic yards and bags of concrete for continuous footings.
Gravel Calculator
Find tons and cubic yards of gravel or crushed stone for driveways and paths.
Concrete Cost Calculator
Estimate the total cost of concrete by entering a price per cubic yard.