Concrete Calculator

Ordering concrete is one of those tasks that feels straightforward until a truck arrives with half a metre too little and the whole pour stops while you scramble. The good news is the numbers are simple: a slab is length times width times thickness, a column is a cylinder, and the cement, sand and stone are then split out of that volume using the mix ratio. The details — the 1.54 dry-volume factor, the waste allowance, the water-cement ratio — are what turn a rough guess into a quantity you can actually order.

Concrete Calculator estimates the volume of concrete you need for slabs, beams, square and round columns, and trapezoidal footings, then breaks that volume down into bags of cement, sand, coarse aggregate and water for every common mix grade from M5 to M25. Choose metric or imperial units, set the mix and the bag size, add a waste allowance, and read off your materials in cubic metres, kilograms and tonnes.

Underneath the inputs is a learning guide that explains what the mix ratios mean, why the dry volume is higher than the finished volume, how much concrete one bag makes, and which grade to use where. Everything runs in your browser; nothing is uploaded.

• Five shapes: Rectangular slab, beam or wall, square column, round column, and trapezoidal footing — the shapes that cover nearly every concrete pour.
• Volume in any unit: Metres, centimetres, millimetres, feet, inches or yards for the dimensions, with volume always reported in cubic metres, feet and yards.
• All common mix grades: M5 (1:5:10), M7.5 (1:4:8), M10 (1:3:6), M15 (1:2:4), M20 (1:1.5:3), M25 (1:1:2), plus a custom ratio.
• Cement bags breakdown: Bags of cement needed (25, 40 or 50 kg), exact fractional value and rounded-up order quantity.
• Full material bill: Sand and coarse aggregate volumes with kilogram and tonne conversions using standard bulk densities.
• Water estimate: Litres of water from the water-cement ratio, automatically set to the recommended value for each grade.
• Waste & dry factor: Adjustable waste allowance and the standard 1.54 dry-volume factor, so the estimate matches real site wastage.
• Reverse converter: Enter any volume in cubic metres, feet or yards and get the materials for it without drawing a shape.
• Live estimate: The concrete volume and bag count update as you type, with a working-through line that shows the maths.
• Export your estimate: Copy or download the full breakdown as text, CSV or JSON for use in a quote or spreadsheet.
• Learning guide: Mix-grade table, cement yield per bag, water-cement guidance, shape formulas and practical site tips built into the tool.

1. Pick the shape. Slab for floors and pads, beam for beams and walls, square or round column for vertical members, and trapezoid footing for spread footings.
2. Enter the dimensions. Use the unit selector first so the numbers you type are in the unit you think they are.
3. Choose the mix grade. Start with M15 (1:2:4) for general reinforced work; switch to M20 or M25 for heavier structures.
4. Select the bag size. 50 kg is the standard construction bag; 25 kg and 40 kg are common for retail and repair work.
5. Set the waste allowance. 5 percent is a sensible default for site wastage, spillage and levelling.
6. Read the estimate. Concrete volume and cement bags appear instantly, with sand, aggregate, water and weight beneath.
7. Review the working. The maths line shows wet volume, dry volume and the division into parts so you can verify every number.
8. Export the bill. Copy or download the summary as text, CSV or JSON for your quote, order or spreadsheet.
9. Or use the converter. Jump straight to material quantities from any volume without drawing a shape.
10. Check the guide. The learning tab explains mix grades, yields, water-cement ratios and which concrete goes where.

Example 1 — House slab. A 5 m × 3 m floor slab at 0.15 m thick holds 2.25 m³. On a 1:2:4 mix with 5 percent waste this is 15 bags of 50 kg cement, about 1.04 m³ sand and 2.08 m³ coarse aggregate.

Example 2 — Round column. Four columns, each 0.3 m across and 3 m tall, hold about 0.21 m³ each for a total of 0.85 m³. At M20 that works out to roughly 8.1 bags of cement per cubic metre.

Example 3 — Trapezoidal footing. A footing 1.2 m square at the base, 0.5 m square at the top and 0.3 m high holds about 0.30 m³ (the volume of a prismoid, not a plain box).

Example 4 — Concrete to a volume. Using the converter, order 10 m³ of M15 from a ready-mix plant: the estimate says about 63 bags of cement-equivalent, 4.6 m³ sand and 9.2 m³ stone if you batch it on site.

Example 5 — Checking a quote. A contractor quotes for a 2.5 m³ patio at M15. The calculator gives 16 bags of cement, 1.15 m³ sand and 2.31 m³ aggregate before waste — a quick cross-check that keeps your order honest.

• Order the right amount: Stop the short-pour panic with volume and bag quantities you can trust before the truck leaves the plant.
• Know your materials: Cement, sand, aggregate and water all come out in the units you buy in — volumes, kilograms and tonnes.
• Pick the right grade: The mix table shows which ratio carries which strength and where each grade belongs on the site.
• Work in any unit: Mix metric and imperial freely; every output converts in all three volume units.
• Verify the maths: The working-through line shows wet volume, dry factor and parts so nothing is a black box.
• Batch or ready-mix: Estimate site-batched bags or convert a ready-mix volume — the calculator does both.
• Export the bill: Text, CSV and JSON summaries drop straight into quotes, purchase orders and spreadsheets.
• Free and private: No account, no watermark, nothing uploaded.