About the Concrete Mix Ratio Calculator
This concrete mix ratio calculator breaks a finished (wet) concrete volume into the dry ingredients you need to mix it yourself: bags of cement, the volume and weight of sand and gravel, and the water for your chosen water–cement ratio. Pick a common nominal mix such as 1:2:3 or 1:2:4, or type your own cement : sand : gravel parts.
It is meant for DIYers and small builders batching concrete on site with a mixer or by hand — footings, fence posts, patios, pads and small slabs — and for anyone checking how much cement is really in a recipe. Results are shown in cubic feet, pounds and US gallons (imperial) or cubic metres, kilograms and litres (metric).
The method is the standard dry-volume approach: loose dry materials shrink when water is added and voids fill, so the dry volume is taken as about 1.54 times the wet volume before it is shared out by the ratio. Bulk densities of 1,440 kg/m³ for cement, 1,600 kg/m³ for dry sand and 1,500 kg/m³ for gravel are typical averages; damp sand bulks up, so weigh or adjust on site. For structural work, follow the mix design your engineer or ready-mix supplier specifies.
With the default inputs, the cement bags is 7. Change any value above to recalculate instantly.
How to use the concrete mix ratio calculator
- 1Choose imperial or metric units and enter the volume of concrete you need (use a concrete volume calculator first if needed).
- 2Pick a nominal mix ratio, or choose Custom and enter your own cement, sand and gravel parts.
- 3Set the water–cement ratio and the cement bag size you can buy.
- 4Adjust the waste allowance (5–10% is common for hand mixing).
- 5Read off the cement bags, sand, gravel and water, and batch them in the same proportions.
Formula and method
Concrete ingredients are measured loose and dry, but once water is added the fine particles fill the gaps between the stones and the mix shrinks. To end up with the wet volume you need, the calculator first multiplies it by your waste allowance and by the dry volume factor (1.54 by default, the common site rule; values between about 1.52 and 1.57 are used). That dry volume is then shared out in proportion to the cement : sand : gravel parts of the ratio.
Volumes are converted to weights using typical loose bulk densities — 1,440 kg/m³ for cement, 1,600 kg/m³ for dry sand and 1,500 kg/m³ for gravel. Water is the water–cement ratio times the cement weight (1 kg of water is 1 litre). Cement is rounded up to whole bags. Nominal mixes like these are a recipe, not a strength guarantee; real strength depends on water content, aggregate quality, mixing and curing.
- Vwet
- Finished concrete volume required
- Vdry
- Total loose dry material volume
- parti
- Parts of cement, sand or gravel in the ratio
- w/c
- Water–cement ratio by weight
Worked examples
One cubic yard of 1:2:3 general-purpose concrete
One cubic yard is 0.7646 m³; adding 5% waste gives 0.8028 m³, and ×1.54 gives 1.2363 m³ of loose dry material. Cement is 1 of 6 parts: 0.2060 m³ × 1,440 kg/m³ = 296.7 kg (654 lb), which is 6.96 → 7 bags of 94 lb. Sand is 2/6 (14.55 cu ft, about 1,454 lb), gravel 3/6 (21.83 cu ft, about 2,044 lb), and water at w/c 0.5 is 148.4 L or 39.2 gallons.
One cubic metre of 1:2:4 for footings (metric, 50 kg bags)
1 m³ plus 5% waste is 1.05 m³, and the dry volume is 1.05 × 1.54 = 1.617 m³. With 7 parts in total, cement is 1.617 ÷ 7 = 0.231 m³ = 332.6 kg, or 6.65 → 7 bags of 50 kg. Sand is 0.462 m³ (739 kg), gravel 0.924 m³ (1,386 kg) and water 0.5 × 332.6 = 166 L.
Two cubic yards of strong 1:1.5:3 mix with less water
Two cubic yards (1.5291 m³) plus 10% waste is 1.682 m³, giving 2.590 m³ of dry material. Cement is 1 of 5.5 parts: 0.4710 m³ = 678.2 kg (1,495 lb), so 15.9 → 16 bags of 94 lb. Sand is 24.95 cu ft, gravel 49.9 cu ft, and water at w/c 0.45 is 305 L (80.6 gallons).
Frequently asked questions
What is the best concrete mix ratio?+
For general DIY work such as patios, paths and garden slabs, 1 part cement, 2 parts sand and 3 parts gravel (1:2:3) is a reliable all-rounder. Footings and foundations commonly use 1:2:4, lean blinding layers 1:3:6, and stronger structural mixes 1:1.5:3. Always follow an engineer or local code where strength is specified.
How many bags of cement are in a cubic yard of concrete?+
With the dry-volume method, a 1:2:3 mix needs about 6.6 bags of 94 lb portland cement per cubic yard before waste (7 bags with 5% waste), and a 1:2:4 mix about 5.7 bags. A richer 1:1.5:3 mix uses roughly 7.2 bags. Pre-mixed 80 lb bags of concrete are different: about 45 of them make a cubic yard.
Why multiply the wet volume by 1.54?+
Loose cement, sand and gravel contain air voids. When water is added and the mix is compacted, sand fills the gaps between stones and cement fills the gaps in the sand, so the dry pile shrinks by roughly a third. Multiplying by about 1.54 (some use 1.52–1.57) converts the wet volume you need into the dry volume to buy.
How much water do I add to concrete?+
Use the water–cement ratio by weight: at 0.5, every 94 lb bag of cement needs 47 lb of water, about 5.6 US gallons, and every 50 kg bag needs 25 litres. Lower ratios (0.40–0.45) give stronger, more durable concrete but are stiffer to place. Remember damp sand already carries water, so add slowly.
Is the mix ratio by volume or by weight?+
Nominal ratios such as 1:2:3 are traditionally measured by loose volume — buckets or shovels of each material. This calculator gives both volumes and approximate weights using typical bulk densities, so you can batch either way. The water–cement ratio, by contrast, is always by weight.