Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Concrete needed
2.72
cubic yards (with waste)
Cubic feet (no waste)
66.7
60-lb bags (estimate)
163
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter length (ft).
- 2Enter width (ft).
- 3Enter thickness (in).
- 4Enter waste / overage (%).
- 5Read your concrete needed on the right — it updates as you type.
- 6Hit Share to keep the scenario or send it to someone.
About this calculator
Estimate concrete volume for a rectangular slab from length, width, and thickness.
Worked example
Using the values the calculator loads with:
Inputs
- Length: 20 ft
- Width: 10 ft
- Thickness: 4 in
- Waste / overage: 10 %
Results
- Concrete needed: 2.72
- Cubic feet (no waste): 66.7
- 60-lb bags (estimate): 163
What each field means
Inputs
- Length (ft)
- The length used in the calculation, measured in ft. Starts at 20 ft so you have a working example on load.
- Width (ft)
- The width used in the calculation, measured in ft. Starts at 10 ft so you have a working example on load.
- Thickness (in)
- The thickness used in the calculation, measured in in. Starts at 4 in so you have a working example on load.
- Waste / overage (%)
- The waste / overage used in the calculation, measured in %. Starts at 10 % so you have a working example on load.
Results
- Concrete needed
- cubic yards (with waste)
- Cubic feet (no waste)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- 60-lb bags (estimate)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the concrete calculator work?
Estimate concrete volume for a rectangular slab from length, width, and thickness.
What do I need to enter?
4 values: length, width, thickness, and waste / overage. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the concrete needed result mean?
cubic yards (with waste) It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Estimates assume standard, average conditions — local rules, pricing, and materials vary.
Who is this tool for?
It's built for anyone doing everyday planning maths — a quick estimate that would otherwise need four browser tabs and a calculator app.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Concrete Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/concrete
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/concrete" target="_blank" rel="noopener">Concrete Calculator — RevenueLab</a> (2026).</p>
Source: [Concrete Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/concrete) (2026).