About Concrete Volume Calculator
The concrete volume calculator estimates how much concrete you need for a slab, footing, column, or beam, and converts the result between cubic metres and cubic yards. Enter the member dimensions in metres and the tool returns the in-place volume, a volume including a waste allowance, the number of premix bags, and an approximate cement, sand, and aggregate breakdown.
Volume is the product of the cross-section and the member length: a slab is length x width x thickness, a footing is length x width x depth, a rectangular column is width x depth x height, a circular column is pi/4 x diameter squared x height, and a beam is width x depth x length. A count multiplier scales the result for repeated members, and the nominal mix ratio (such as 1:2:4) splits the dry volume into its constituent materials.
How It Works
- Pick a shape: slab, footing, rectangular column, circular column, or beam.
- Enter the member dimensions in metres and, optionally, a count for repeated members.
- Set a waste allowance percentage and the finished-concrete yield per premix bag.
- Choose a nominal mix ratio; the tool returns volume (m^3 and yd^3), bags, and cement / sand / aggregate quantities.
Worked Example
Take the classic 10 x 10 ft slab poured 4 in thick. Converted to metres the inputs are 3.048 x 3.048 m with a 0.1016 m thickness, so the in-place volume is 3.048 x 3.048 x 0.1016 = 0.944 m^3. A 10% waste allowance brings the order to 0.944 x 1.10 = 1.04 m^3, which is 1.04 / 0.764555 = 1.36 cubic yards. Mixing from 80 lb premix bags at a 0.017 m^3 (about 0.60 ft^3) finished yield each — enter 0.017 in the bag-yield field — the bag count rounds up to 62 bags. Mixing 62 bags by hand is a full day of work, so at this size it is worth pricing a short-load ready-mix delivery against the bagged route before buying.
How much concrete do I need for a slab, footing, or pier?
The table below covers the slab and footing sizes people most often price out, computed with this calculator. Every row includes a 10% waste allowance and counts 80 lb premix bags at a 0.017 m³ (≈0.60 ft³) yield — the value to enter in the bag-yield field.
| Project | Concrete needed (m³) | Cubic yards | 80 lb bags |
|---|---|---|---|
| 10 × 10 ft slab, 4 in thick | 1.04 | 1.36 | 62 |
| 12 × 12 ft patio slab, 4 in thick | 1.50 | 1.96 | 88 |
| 20 × 20 ft two-car driveway, 4 in thick | 4.15 | 5.43 | 245 |
| 24 × 24 ft garage slab, 6 in thick | 8.97 | 11.73 | 528 |
| 20 ft strip footing, 16 in wide × 8 in deep | 0.55 | 0.72 | 33 |
| Six 12-in sonotube piers, 4 ft deep | 0.59 | 0.77 | 35 |
Formulas
- Slab / footing volume
V = L * W * t- Rectangular column volume
V = W * d * H- Circular column volume
V = (pi / 4) * D^2 * H- Total volume with waste & yards
V_total = V_net * count * (1 + waste/100) ; V_yd3 = V_m3 / 0.764555- Material breakdown (nominal mix)
V_dry = V_total * dryFactor ; cement = V_dry * c/(c+s+a) ; mass = V * 1440
Standards & References
- ACI 211.1 nominal concrete mixes
- 1 cubic yard = 0.764554857984 cubic metres
- Cement bulk density ~1440 kg/m^3
Frequently Asked Questions
How many 25 kg bags of premix concrete do I need per cubic metre?
A 25 kg bag of dry premix yields roughly 0.0125 to 0.0166 m^3 of finished concrete, so you need about 60 to 80 bags per cubic metre. Always check the yield printed on the bag, since it varies by product, and enter that figure in the bag-yield field.
How do I convert cubic metres of concrete to cubic yards?
Divide the volume in cubic metres by 0.764555 (one cubic yard equals 0.764555 m^3). For example, 3.0 m^3 is 3.0 / 0.764555 = 3.92 cubic yards. The calculator reports both units automatically.
Why should I add a waste allowance?
Spillage, over-excavation, uneven subgrade, and pump losses mean you almost always place more concrete than the theoretical volume. A waste allowance of 5 to 10 percent is typical for slabs and footings; add more for rough ground or small pours.
How many bags of concrete do I need for a 10x10 slab?
A 10 x 10 ft slab poured 4 in thick needs 62 bags of 80 lb premix, counting a 10% waste allowance and a 0.017 m^3 (about 0.60 ft^3) finished yield per bag. That corresponds to 1.36 cubic yards with waste included; at 6 in thick the same slab needs half again as much.
How many 80 lb bags of concrete are in a cubic yard?
A cubic yard is 27 cubic feet, and an 80 lb bag of premix yields about 0.60 ft^3 of placed concrete, so a yard takes 27 / 0.60 = 45 bags. Smaller bags scale accordingly: a 60 lb bag yields about 0.45 ft^3 (60 bags per yard). Enter the yield printed on your bag to get an exact count.
How much concrete do I need for a 24x24 garage slab?
At the common 6 in thickness, a 24 x 24 ft garage slab needs 11.73 cubic yards (8.97 m^3) including a 10% waste allowance, as computed in the table above. A quantity that size is ready-mix territory rather than bagged premix — the equivalent bag count is 528 bags of 80 lb mix.
What does the 1:2:4 mix ratio mean?
It is the ratio of cement to fine aggregate (sand) to coarse aggregate by volume, a nominal mix of roughly C20 strength. The dry volume is multiplied by a bulking factor (about 1.54) because the combined dry materials compact when water is added, then split into the three parts.