Concrete Calculators
Work out volume, bag counts, rebar and installed cost for any pour.
Concrete calculators turn the dimensions of a form into an orderable quantity — cubic yards for a ready-mix truck, bag counts for a mixer, and the cost of both. That conversion is where most concrete projects go wrong, because the measurements arrive in three different units at once: length and width in feet, thickness in inches, and the order in cubic yards.
Every calculator in this category handles that conversion and shows the arithmetic it used. Set your own waste allowance, switch between imperial and metric, and read the ordering figure directly. Nothing is rounded in our favour and no constant is hidden.
Calculators in this category
Who these calculators are for
Homeowners planning a pour
You want to know what a 24 × 24 garage slab should cost before three contractors quote you wildly different numbers. Knowing the pour is 7.1 cubic yards tells you immediately whether a quote is priced on volume or on optimism.
DIYers deciding bags vs ready-mix
The crossover is around one cubic yard — 45 eighty-pound bags, roughly 3,600 lb to carry and mix by hand. Below that, bags win. Above it, a truck is cheaper and far less punishing. The calculators give you both figures so the decision is obvious.
Contractors and estimators
Quick takeoffs on site, in the truck, or on the phone with a supplier. Slab, footing and column modes cover most residential forms, and results are shareable as a link with the inputs preserved.
Anyone checking a supplier order
A short-load fee or an over-order is expensive in both directions. Running the numbers yourself before the truck is scheduled catches a mis-keyed dimension while it is still free to fix.
How they help
They keep the units straight
Thickness is entered in inches, length and width in feet, and the answer comes back in cubic yards. Doing that by hand means dividing by 12, then by 27, and the single most common concrete ordering error is forgetting one of those steps — which puts you out by a factor of twelve.
They make waste explicit
Real pours consume more than the geometry says: spillage, an uneven subgrade, over-excavated trenches. Most tools bury a fixed allowance in the result. Here it is a field you control, and you see the raw volume and the order volume side by side.
They convert to what you actually buy
Nobody sells cubic feet. You buy cubic yards from a plant or bags from a merchant, so the results show cubic yards, 80 lb bag count and 60 lb bag count together — the three numbers a supplier will ask you for.
They show the formula
Every result prints the expression behind it. If a number looks wrong you can check it in thirty seconds rather than guessing whether the tool assumed a different density.
Worth saving for next time
Concrete work is rarely one calculation. You size the slab, then the footings, then price the rebar, then re-run everything when the design moves by two feet. Having the whole set in one place — with the same waste allowance and the same assumptions across all of them — is faster than reaching for a different site each time.
Results are shareable as a link with your inputs preserved, and printable as a clean job sheet with the formula on it. Bookmark the hub rather than a single tool: the calculators here cross-reference each other, and the set grows.
Concrete guides
Concrete Slab Cost per Square Foot — A standard broom-finish slab installs at $6–$12 per square foot in 2026. This guide shows where in that range your project lands, and what the per-square-foot number hides.
How to Calculate Concrete for a Slab — Length × width × thickness, ÷ 27, plus waste. Four steps, two unit conversions, and one worked example you can follow with a pencil.
Concrete calculator FAQ
How many cubic yards of concrete do I need?
Multiply length by width in feet, multiply by thickness in feet (inches ÷ 12), then divide by 27. A 24 × 24 ft slab at 4 inches is 192 cubic feet, or 7.11 cubic yards. Add 5–10% waste and order 8.
How many bags of concrete are in a cubic yard?
45 eighty-pound bags, 60 sixty-pound bags, or 72 fifty-pound bags. An 80 lb bag yields about 0.6 cubic feet, and there are 27 cubic feet in a cubic yard.
When is ready-mix cheaper than bags?
Around one cubic yard. At that point you are mixing 45 bags — about 3,600 lb of material — by hand. Ready-mix is cheaper per yard above that, though most plants add a short-load fee below 3–4 yards, so the 1–3 yard range is genuinely a judgement call.
How thick should a concrete slab be?
4 inches suits patios, walkways and shed bases. Use 5–6 inches for driveways and anything carrying vehicles, and thicker still for heavy equipment. Thickness for anything structural should come from an engineer, not a calculator.
How much waste should I allow on a concrete order?
5–10% on a well-prepared flat subgrade. Go to 15% for hand-dug footing trenches, irregular forms, or ground that has not been properly levelled — over-excavation quietly swallows concrete.
Are these concrete calculators free?
Yes. No account, no limit on calculations, and no paywalled results. The site is funded by advertising.