Concrete Calculator
Estimate concrete volume for a rectangular slab in US or metric units using length, width and thickness, with optional waste, bag-yield and material-cost estimates.
Best for: patios, pads, walkways and other rectangular slab-style projects. Irregular shapes, cylindrical post holes and separate footings may need to be calculated individually.
Estimate Your Concrete Needs
Calculate concrete volume for a rectangular slab, including waste allowance, optional bag quantities, and material cost.
For bag estimates, enter the concrete yield printed on your product packaging. Bag weight alone is not used because yield can vary by product and market. Currency selection only changes how your entered price is displayed; no exchange-rate conversion is performed.
A Practical Concrete Estimate
Concrete Volume
See the required concrete volume in cubic feet and cubic yards or cubic meters after your selected waste allowance is applied.
Bag Estimate
Enter the yield printed on your concrete mix packaging to estimate how many bags the project requires.
Optional Cost
Enter a price per cubic yard or cubic meter and choose a currency to estimate material cost before delivery, labor and other project charges.
How to Use the Concrete Calculator
- Choose US Units or Metric Units, then enter the slab length and width in the units shown.
- Enter slab thickness in inches for US mode or centimeters for Metric mode.
- Add a waste allowance for variations in excavation, form dimensions and placement.
- If you plan to use bagged concrete, enter the yield per bag shown on the product packaging: cubic feet per bag in US mode or cubic meters per bag in Metric mode.
- Choose your currency, then enter the concrete price per cubic yard in US mode or per cubic meter in Metric mode for an optional material-cost estimate.
- Select Calculate to see the required concrete volume in the selected unit system, plus optional bag and cost estimates.
How the Concrete Estimate Works
The calculator multiplies slab length by width and thickness using the selected unit system. It normalizes the measurements internally, calculates the base volume, then applies the waste allowance.
Core formulas
Slab volume = length × width × thickness, using consistent units
US volume = cubic feet, with cubic yards also shown
Metric volume = cubic meters
Waste-adjusted volume = base volume × (1 + waste percentage)
In US mode, the calculator shows cubic feet and cubic yards. In Metric mode, it shows cubic meters. The selected waste allowance is applied to the base volume to produce a more practical purchasing estimate.
If you enter a bag yield, the tool estimates the number of bags by dividing the waste-adjusted concrete volume by the yield of one bag and rounding up. Because yield varies by product and market, use the value printed on the actual packaging.
Concrete Planning Reference
Concrete requirements depend on the actual dimensions and conditions of the project. These values explain how the calculator handles US and metric measurements, bag yield and optional pricing.
| Measurement | Reference |
|---|---|
| US dimensions | Length and width in feet; thickness in inches |
| Metric dimensions | Length and width in meters; thickness in centimeters |
| Slab volume | Length × width × thickness |
| US volume result | Cubic feet and cubic yards |
| Metric volume result | Cubic meters |
| Waste allowance | Added after base volume is calculated |
| Bag estimate | Waste-adjusted volume ÷ user-entered product yield per bag, rounded up |
| Optional cost | Recommended volume × entered price per cubic yard or m³, shown in the selected currency |
Concrete Calculator Example
Suppose you are planning a 10 ft × 10 ft concrete slab that is 4 inches thick. You include a 10% waste allowance, enter a concrete-bag yield of 0.60 cu ft per bag, and use a ready-mix price of $150 per cubic yard in USD.
- Concrete before waste: approximately 33.33 cu ft (1.23 cu yd)
- Waste-adjusted concrete volume: approximately 36.67 cu ft (1.36 cu yd)
- Approximate bags required: 62 bags when each bag yields 0.60 cu ft
- Estimated concrete material cost: approximately $203.70
Metric equivalent: The same slab is approximately 3.048 m × 3.048 m and 10.16 cm thick. Using the equivalent bag yield of about 0.01699 m³ per bag and a price of about $196.19 per m³, the calculator returns approximately 1.038 m³, 62 bags, and the same material cost of about $203.70.
This example is for planning only. Product yield, actual placement conditions, delivery charges and other project costs can change the final amount required.
Frequently Asked Questions
How many cubic feet are in a cubic yard of concrete?
One cubic yard contains 27 cubic feet. In US mode, the calculator shows both cubic feet and cubic yards automatically; Metric mode reports cubic meters.
Should I include extra concrete for waste?
A waste allowance can help account for differences between planned and actual dimensions, uneven excavation, spills and other small variations. The appropriate allowance depends on the project.
How accurate is the concrete bag estimate?
The bag result is based on the yield per bag that you enter. Use the yield printed on the specific concrete mix you plan to buy, because bag weight alone does not guarantee a universal yield.
Can I use metric measurements?
Yes. Choose Metric Units to enter length and width in meters, thickness in centimeters, bag yield in cubic meters per bag, and concrete price per cubic meter. The recommended volume is then shown in cubic meters.
Why does the calculator ask for bag yield instead of bag weight?
Concrete products can have different yields even when bag weights look similar. Entering the yield printed on the actual product packaging makes the bag estimate more useful across different products and countries.
Does changing the currency convert concrete prices automatically?
No. The currency selector only controls how the cost is labeled and formatted. Enter the actual price for your chosen currency; the calculator does not use live exchange rates.
Does the cost estimate include labor or delivery?
No. The optional cost estimate is based only on the concrete price per cubic yard or cubic meter that you enter. Delivery charges, short-load fees, labor, reinforcement, forms, finishing and other project costs are not included.
Can I use this calculator for footings, posts or irregular shapes?
This version is designed for rectangular areas using length, width and thickness. Projects with cylindrical holes, separate footings or irregular shapes may need to be calculated as individual sections or with a calculator designed for those shapes.
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