Concrete Calculator
Enter the size of your slab, footing, wall, beam or column to find how much concrete you need in cubic metres, cubic yards and cubic feet, along with the cement, sand and aggregate for your mix.
Your calculation is performed in your browser.How it works
The calculator finds the volume of one item from its dimensions: length × width × thickness for a slab, footing, wall or beam, or π × radius² × height for a round column. It multiplies by the number of identical items, adds your wastage allowance, and shows the total in cubic metres, cubic yards and cubic feet. It then splits that volume into cement, sand and coarse aggregate using the nominal mix ratio you pick.
Formula & methodology
Concrete volume is the space the concrete fills, so every length is first converted to metres. The wastage allowance is a percentage added on top of the net volume. To work out materials, the calculator uses the dry volume method: wet concrete needs about 1.54 times its volume in dry cement, sand and aggregate, because the dry materials contain air voids that fill up when water is added. That dry volume is divided between cement, sand and aggregate in the mix ratio. Cement volume is converted to weight at 1,440 kg/m³ and to 50 kg bags, which are rounded up. Sand and aggregate are also shown in tonnes using typical bulk densities of 1,600 and 1,500 kg/m³.
Volume = Length × Width × ThicknessVolume = π × (Diameter ÷ 2)² × HeightNet volume = Volume of one item × Number of itemsTotal = Net volume × (1 + Wastage % ÷ 100)Dry volume = Total × 1.54Material volume = Dry volume × (Material part ÷ Sum of mix parts)Bags = (Cement volume × 1,440) ÷ 50, rounded up1 m³ = 35.3147 ft³ = 1.30795 yd³ | 1 yd³ = 27 ft³ = 0.7646 m³What each term means
- Thickness / depth
- Depth of the pour. Entered in cm or inches and converted to metres.
- Wastage %
- Extra concrete for spillage, uneven ground and over-excavation. 5–10% is typical.
- Mix ratio
- Cement : sand : coarse aggregate by volume, such as 1 : 1.5 : 3 for M20.
- 1.54
- Dry volume factor that accounts for voids in the dry materials.
Materials per 1 m³ of concrete by nominal mix (before wastage)
| Grade | Mix (C : S : A) | Cement (50 kg bags) | Sand (m³) | Aggregate (m³) |
|---|---|---|---|---|
| M5 | 1 : 5 : 10 | 2.8 | 0.48 | 0.96 |
| M7.5 | 1 : 4 : 8 | 3.4 | 0.47 | 0.95 |
| M10 | 1 : 3 : 6 | 4.4 | 0.46 | 0.92 |
| M15 | 1 : 2 : 4 | 6.3 | 0.44 | 0.88 |
| M20 | 1 : 1.5 : 3 | 8.1 | 0.42 | 0.84 |
| M25 | 1 : 1 : 2 | 11.1 | 0.39 | 0.77 |
Worked example
A garage slab that is 5 m long, 4 m wide and 150 mm (15 cm) thick has a volume of 5 × 4 × 0.15 = 3 m³. Adding 5% wastage gives 3.15 m³, which is about 4.12 cubic yards. For an M20 (1 : 1.5 : 3) mix you need roughly 26 bags of 50 kg cement, 1.32 m³ of sand and 2.65 m³ of coarse aggregate. In imperial units, a 10 ft × 10 ft patio that is 4 inches thick needs 100 × (4 ÷ 12) = 33.3 cubic feet, or about 1.23 cubic yards, before wastage.
Common uses
- —Working out how many cubic yards or cubic metres of ready-mix concrete to order for a slab, driveway or patio.
- —Estimating cement bags, sand and aggregate for a site-mixed foundation, footing or column.
- —Checking a contractor’s or supplier’s concrete quantity before you approve it.
- —Budgeting the concrete portion of a build alongside your overall construction cost.
Important notes
- —This is a planning estimate. Always order a little extra, because over-excavation, uneven sub-base and formwork movement all use more concrete than the drawings show.
- —Nominal mix ratios and bag counts are approximations. Structural concrete such as beams, columns and suspended slabs should follow the grade and mix design specified by your structural engineer.
- —Ready-mix suppliers sell by the cubic metre or cubic yard and usually have a minimum order. Confirm quantity, slump and delivery details with your supplier.
- —Reinforcement steel, formwork, sub-base, curing and finishing are not included in this calculation.