Concrete Calculator
Enter the length, width and thickness of a slab to see how much concrete to order, in cubic yards and cubic meters. Choose imperial or metric units and add a waste allowance for spills and uneven ground.
Last updated November 2, 2026
Extra for spills and uneven ground
Result
1.358 cubic yards (1.038 m³)
Order total with waste, about 36.667 cubic feet.
| Amount | Cubic yards | Cubic meters |
|---|---|---|
| Slab volume | 1.235 | 0.944 |
| Waste (10%) | 0.123 | 0.094 |
| Order total | 1.358 | 1.038 |
Volume = length × width × thickness. Suppliers set their own minimum loads and rounding, so confirm the quantity with yours.
Show the work
Formula: volume = length x width x thickness; order = volume x (1 + waste / 100)
- Slab: 10 ft x 10 ft x 4 in.
- Volume: 0.944 m³ = 1.235 cubic yards (1 yd³ = 0.9144³ m³ = 27 ft³).
- Waste: 1.235 x 10% = 0.123 cubic yards.
- Order total: 1.235 + 0.123 = 1.358 cubic yards (1.038 m³, 36.667 ft³).
Result: 1.358 cubic yards (1.038 m³)
How the concrete volume is worked out
volume = length × width × thickness
order = volume × (1 + waste ÷ 100)
A flat slab is a box, so its volume is its length times its width times its thickness. Length and width are entered in feet or meters and thickness in inches or centimeters, and the calculator converts everything to meters before multiplying. A 10 ft by 10 ft slab that is 4 in thick is 10 × 10 × 4/12 = 33.33 cubic feet.
Concrete is sold by the cubic yard in the United States and by the cubic meter in most other countries. One cubic yard is 27 cubic feet, or 0.7646 cubic meters, so 33.33 cubic feet is 33.33 ÷ 27 = 1.23 cubic yards, or 0.944 cubic meters. Both units are shown.
The waste allowance is added on top of that volume. At 10 percent the 1.23 cubic yards become 1.23 × 1.10 = 1.36 cubic yards. The result covers a plain slab only. Footings, steps and thickened edges add volume, so work those out separately and add them.
See how we calculate for the formulas, sources and review schedule behind every calculator.
Also useful alongside this calculator: Volume Calculator, Length Converter and Percentage Calculator.
How much extra to order
Ground is never perfectly level, forms bulge a little under wet concrete, and some mix is lost in the barrow and the tools. A shortfall in the middle of a pour costs far more than a little leftover, because fresh concrete cannot be topped up later without a visible joint.
The calculator starts at 10 percent, a common allowance for a simple slab. Use less for a flat, well-prepared base and more for rough ground or a long barrow run. You can enter any value from 0 to 100 percent.
Choosing a thickness
Thickness has a direct effect on the amount. Doubling it doubles the concrete: the same 10 ft by 10 ft slab needs 1.23 cubic yards at 4 inches and 2.47 at 8 inches. Patios and walkways are commonly poured about 4 inches thick, while driveways and garage floors that carry vehicles are often thicker.
The right figure depends on the load, the ground and local building rules, so confirm it with your plans or contractor. This calculator measures the volume you give it and does not judge whether a thickness is suitable.
Estimating bags of mix
For small jobs you may buy bags instead of a truckload. Each bag prints how much finished concrete it makes, called its yield, and that number varies between brands and sizes. Divide your order total in cubic feet by the yield of one bag and round up.
For example, if a bag yields 0.6 cubic feet and the slab with waste needs 36.67 cubic feet, you need 36.67 ÷ 0.6 = 61.1, so 62 bags. Read the yield on the bag you actually plan to buy before you rely on this.
Metric and imperial units
Switching the unit setting converts the values already entered, so 10 feet becomes 3.05 meters and 4 inches becomes 10.16 centimeters. Values are rounded to two decimals, so re-enter your measurements if exactness matters.
How to use the Concrete Calculator
- Choose imperial (feet and inches) or metric (meters and centimeters).
- Enter the length and width of the slab, then its thickness.
- Set a waste percentage, 10 percent by default.
- Read the order total in cubic yards and cubic meters, then use Copy, Print or Share.
Worked example
A 12 ft by 12 ft patio that is 4 in thick is 12 × 12 × 4/12 = 48 cubic feet, which is 48 ÷ 27 = 1.78 cubic yards or 1.36 cubic meters. With 10 percent waste the order becomes 1.78 × 1.10 = 1.96 cubic yards, or 1.50 cubic meters. In metric, a 3 m by 3 m slab that is 10 cm thick is 3 × 3 × 0.10 = 0.9 cubic meters, or 1.18 cubic yards.
| Slab size | Cubic feet | Cubic yards | Cubic meters |
|---|---|---|---|
| 10 ft × 10 ft | 33.33 | 1.23 | 0.94 |
| 10 ft × 12 ft | 40 | 1.48 | 1.13 |
| 12 ft × 12 ft | 48 | 1.78 | 1.36 |
| 10 ft × 20 ft | 66.67 | 2.47 | 1.89 |
| 20 ft × 20 ft | 133.33 | 4.94 | 3.78 |
| 24 ft × 24 ft | 192 | 7.11 | 5.44 |
Frequently asked questions
How many cubic yards of concrete do I need for a 10 by 10 slab?
A 10 ft by 10 ft slab that is 4 inches thick needs 1.23 cubic yards, or 1.36 cubic yards with 10 percent waste.
How do I convert cubic feet to cubic yards?
Divide by 27, because a cubic yard is 3 ft by 3 ft by 3 ft. For example, 54 cubic feet is 2 yards.
How much waste should I add?
Ten percent is a common allowance for a simple slab. Add more for uneven ground or a small, awkward pour, and ask your supplier what they advise.
Does this work for footings, steps or round shapes?
It measures a rectangular slab only. For a round footing or a post hole, use the volume calculator with a cylinder, and add the results to your slab total.
Is this a structural or engineering tool?
No. It only calculates volume from the numbers you enter, so check thickness, strength and reinforcement with your plans, your contractor or local building rules. Nothing you enter is stored.