What this calculator does
A concrete mix ratio states the proportions of cement, sand and coarse aggregate by volume, such as 1:2:4 (one part cement, two parts sand, four parts aggregate) or the stronger 1:1.5:3. Builders choose a ratio based on how much load the concrete needs to bear: a footing or driveway slab typically uses a leaner mix like 1:2:4, while structural work often calls for 1:1.5:3 or richer.
This calculator splits a target volume of finished concrete into the volume and weight of each material, given any ratio you enter. It is not locked to one specific mix, because the right ratio depends on the job: enter whatever ratio your project specifies, add a wastage allowance for spillage and over-excavation, and it works out how much of each material to order.
The formula
Add the three ratio parts together to get the total number of parts. Each material then gets that fraction of the total volume: a material with 2 parts out of 7 total gets two-sevenths of the concrete volume. Multiplying each material's volume by its density converts it to a weight in kilograms, which is how cement and aggregate are normally bought.
| Term | Meaning |
|---|---|
| Ratio part | The relative proportion of a material in the mix, such as the 1, 2 and 4 in a 1:2:4 mix. Only the ratio between the numbers matters, not their absolute size. |
| Wastage allowance | Extra volume added to cover spillage, over-excavation and the material lost sticking to mixing equipment. |
| Density | Mass per cubic metre of a material once compacted. Real densities vary with moisture content and particle size, so treat the defaults as reasonable estimates rather than exact figures for your materials. |
The inputs explained
| Field | What to enter |
|---|---|
| Target concrete volume (m³) | The finished volume of concrete you need, in cubic metres. |
| Cement ratio part | The cement portion of the ratio, e.g. the 1 in 1:2:4. |
| Sand ratio part | The sand portion of the ratio, e.g. the 2 in 1:2:4. |
| Aggregate ratio part | The aggregate portion of the ratio, e.g. the 4 in 1:2:4. |
| Wastage allowance (%) | Extra percentage added on top of the target volume to cover spillage and losses. |
| Cement density (kg/m³) | Bulk density of the cement being used. |
| Sand density (kg/m³) | Bulk density of the sand being used. |
| Aggregate density (kg/m³) | Bulk density of the coarse aggregate being used. |
When to use it
A standard 1:2:4 footing or slab
General-purpose concrete for footings, paths and non-structural slabs is commonly specified as 1:2:4, a relatively lean mix that keeps material cost down while still meeting typical load requirements.
A richer structural mix
Load-bearing elements such as columns and beams often call for a richer ratio like 1:1.5:3 or 1:1:2, which uses proportionally more cement for higher strength.
Ordering materials for a job
Once the mix ratio and total volume are set, converting straight to kilograms of cement, sand and aggregate makes it easy to work out how many bags or truckloads to order.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does the material split change across common mix ratios for 1 m³ of concrete?
The same target volume, split according to a few widely used ratios.
| Mix ratio (cement:sand:aggregate parts) | Cement needed | Sand needed | Aggregate needed |
|---|---|---|---|
| 1:1:2 | 302.40 kg | 672.00 kg | 630.00 kg |
| 1:1.5:3 | 252.00 kg | 560.00 kg | 787.50 kg |
| 1:2:4 | 216.00 kg | 480.00 kg | 900.00 kg |
| 1:3:6 | 168.00 kg | 373.33 kg | 1,050.00 kg |
How much material does a 1:2:4 mix need at different volumes?
Cement, sand and aggregate weights for a 1:2:4 mix across a range of job sizes.
| Target volume | Cement needed | Sand needed | Aggregate needed |
|---|---|---|---|
| 0.5 m³ | 108.00 kg | 240.00 kg | 450.00 kg |
| 1 m³ | 216.00 kg | 480.00 kg | 900.00 kg |
| 2 m³ | 432.00 kg | 960.00 kg | 1,800.00 kg |
| 5 m³ | 1,080.00 kg | 2,400.00 kg | 4,500.00 kg |
| 10 m³ | 2,160.00 kg | 4,800.00 kg | 9,000.00 kg |
Questions
What does a ratio like 1:2:4 actually mean?
It is the proportion by volume of cement to sand to coarse aggregate in the dry mix, before water is added. A 1:2:4 mix has one part cement for every two parts sand and four parts aggregate.
Which ratio should I use?
It depends on the structural demands of the job: leaner mixes like 1:2:4 suit footings, paths and non-structural slabs, while richer mixes like 1:1.5:3 or 1:1:2 suit load-bearing structural work. Check the specification for your project or ask a structural engineer if you are unsure.
Why does this calculator use weight, not just volume, for ordering?
Cement and aggregate are almost always sold by weight (bags of cement, tonnes of aggregate), so converting the volume split to kilograms using each material's density makes the figures directly useful for ordering.
Does this account for water?
No. This works out the dry cement, sand and aggregate proportions only. Water content is normally set separately as a water-cement ratio appropriate to the mix and site conditions.
For the total volume and weight of a slab or footing before splitting it into materials, see the concrete volume calculator. To check the compressive strength of a cured sample, use the concrete cylinder strength calculator.