Home calculator
Concrete Calculator
Estimate concrete volume for a simple rectangular slab, pad, or pour.
Enter your dimensions
Current unit: feet. The estimate updates automatically in your browser.
Enter the slab or pour length.
Enter the slab or pour width.
Enter thickness in inches for imperial mode, or centimeters for metric mode.
Optional extra allowance for spills, uneven base, or ordering margin.
Estimated result
Concrete needed
Enter your inputs
Your estimate will appear here automatically once the required inputs are valid.
Guide
How to use this estimate
How the concrete calculator works
This calculator multiplies length, width, and thickness to estimate concrete volume for a simple rectangular slab or pour. In imperial mode, length and width are entered in feet, thickness is entered in inches, and the primary result is shown in cubic yards.
The result is the total finished concrete volume, not cement volume alone. Concrete is usually made from cement, sand or fine aggregate, stone or coarse aggregate, water, and sometimes admixtures. The exact ingredient quantities depend on the chosen mix design, strength requirement, application, and supplier guidance.
What to measure
Measure the length and width of the slab or pour area. Then enter the planned thickness. For imperial mode, enter thickness in inches. For metric mode, enter thickness in centimeters.
Use the result as the finished concrete volume required for the pour. If you are ordering ready-mix concrete, this volume is the quantity to discuss with the supplier. If you are mixing on site, ingredient quantities depend on the selected concrete mix.
Example concrete calculation
- Slab size: 10 feet × 10 feet
- Thickness: 4 inches, which is 0.333 feet
- Base volume: 10 × 10 × 0.333 = 33.33 cubic feet
- Cubic yards: 33.33 ÷ 27 = 1.23 cubic yards
- Equivalent metric volume: about 0.94 cubic meters
Estimated concrete needed before waste: 1.23 cubic yards, equivalent to about 0.94 cubic meters.
Quick reference
| Item | Value | Note |
|---|---|---|
| Imperial volume | ft × ft × in ÷ 12 | Convert thickness from inches to feet before calculating volume. |
| Cubic yards | Cubic feet ÷ 27 | Common ready-mix concrete unit in imperial contexts. |
| Manual bag estimate | Volume ÷ bag yield | Use only the yield printed on your bag or product listing. |
Common mistakes to avoid
- Multiplying feet by inches directly instead of converting thickness first.
- Using bag weight as bag yield.
- Assuming all concrete bags produce the same finished volume.
Frequently asked questions
Why does this calculator show volume instead of bags?
Because this calculator estimates the finished mixed concrete volume required for the pour. Bag sizes, bag yields, and mix designs vary by brand and use case. Weight alone, such as 20 kg or 40 kg, is not enough to calculate finished concrete volume without making assumptions.
How can I estimate bags manually?
If your label lists yield per bag, divide the required volume by that yield and round up. Imperial example: 12 cubic feet needed ÷ 0.6 cubic feet per bag = 20 bags. Metric example: 0.34 cubic meters needed ÷ 0.017 cubic meters per bag = 20 bags.
Is this concrete calculator structural advice?
No. It is only a material quantity estimate for a simple rectangular pour. It does not determine slab strength, reinforcement, soil preparation, drainage, load limits, or building-code requirements.