What this calculator does
The Concrete Calculator tells you how much concrete you need for a rectangular slab, footing or column, or for a round column. Enter the dimensions of the pour; the calculator works out the exact volume, adds a waste allowance for spillage and uneven ground, and — if you choose a mix ratio — estimates the bags of cement and the amounts of sand and gravel needed to mix that concrete yourself.
It works with metric (meters) and imperial (feet) units, and reports the result in cubic meters and cubic yards, so you can order a ready-mix delivery or buy bagged materials with confidence. The page is available in English, Arabic, and Spanish.
How to use the Concrete Calculator
- Choose the shape. Use "Slab / footing" for anything poured as a rectangular prism: floor slabs, foundations, footings, paths and pads. Use "Round column" for cylindrical columns and piers.
- Enter the dimensions in meters or feet. For a slab, enter the length, width and thickness (for example 6 × 4 × 0.15 m). For a round column, enter the diameter and the height.
- Set the waste allowance (5% by default). Use 5–10% for slabs on uneven ground and 10–15% for hand mixing on site or small pours where spillage and residue in the mixer matter.
- Optionally choose a mix ratio to estimate materials: 1:2:4 is a common general-purpose mix, 1:1.5:3 is a stronger mix, and 1:3:6 is a lean mix for blinding or leveling layers.
- Click "Calculate" to see the volume with and without waste, plus the cement bags, sand and gravel if a mix was selected.
Formulas
For a rectangular slab or footing with length L, width W and thickness h, and for a round column with diameter ⌀ and height H:
Material estimates use common rule-of-thumb yields per cubic meter of finished concrete. For the 1:2:4 mix: about 320 kg of cement (roughly 6.5 bags of 50 kg), 0.45 m³ of sand and 0.90 m³ of gravel. For 1:1.5:3: about 380 kg of cement (7.6 bags), 0.42 m³ of sand and 0.84 m³ of gravel. For the lean 1:3:6 mix: about 220 kg of cement (4.4 bags), 0.47 m³ of sand and 0.94 m³ of gravel. Cement bags are always rounded up to a whole bag.
Examples
- A house slab of 6 × 4 m, 15 cm thick, at 5% waste: V = 6 × 4 × 0.15 = 3.6 m³; with waste 3.78 m³ ≈ 4.9 yd³ to order.
- A footing strip of 30 ft × 1.5 ft, 1 ft deep, at 10% waste: V = 45 ft³ = 1.27 m³; with waste 1.4 m³. With a 1:2:4 mix that is roughly 9 bags of cement, 0.63 m³ of sand and 1.26 m³ of gravel.
- A round column of ⌀ 40 cm, 3 m tall, at 5% waste: V = π × 0.2² × 3 = 0.377 m³; with waste 0.396 m³. With a 1:1.5:3 mix that is about 4 bags of cement.
Frequently asked questions
How much waste allowance should I add?
5% is a reasonable default for formwork on reasonably level ground. Use 10% for uneven excavation or thin pours, and 10–15% when hand-mixing on site, where some concrete always stays in the mixer, wheelbarrow and forms.
Should I order ready-mix or mix it myself?
For pours above roughly 1 m³, ordering ready-mix concrete is usually faster, more consistent and often cheaper than hand mixing. The bag, sand and gravel estimates are for on-site mixing with a mixer or by hand.
How many bags of cement do I need per cubic meter?
It depends on the mix. As a rule of thumb: 1:2:4 needs about 6.5 bags of 50 kg per m³, 1:1.5:3 about 7.6 bags, and the lean 1:3:6 mix about 4.4 bags. The calculator applies these factors to the volume including waste.
Why are the sand and gravel quantities larger than the concrete volume?
Cement and water fill the voids between sand grains, and sand fills the voids between gravel pieces, so the sum of the dry ingredients is larger than the finished volume. The rule-of-thumb yields already account for this, which is why they are given per cubic meter of finished concrete.
Does the calculator include rebar or formwork?
No. It estimates the concrete volume and dry ingredients only. Rebar, mesh, formwork, vapor barriers and curing materials must be estimated separately.
Are these material quantities exact?
No. Actual yields depend on the moisture and grading of your sand and gravel and on the exact water-cement ratio. The estimates are deliberately on the safe side, but for structural work follow the mix design specified by your engineer.
Is my data saved or sent anywhere?
No. Every calculation runs in your browser, and nothing you type is stored or sent to a server.
Related calculators
Other free calculators commonly used with this tool: Tile Calculator, Paint Calculator, and Stair Calculator.
Want a deeper walkthrough? Read our concrete volume guide.