Concrete Mix Design Helper
Work out the water-cement ratio, total batch mass and aggregate-to-cement ratio for a concrete mix from the mass of each ingredient per cubic metre. The water-cement (w/c) ratio is the number that most controls strength and durability, so it is the first thing to check on any mix.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the cement content and water content in kilograms per cubic metre (kg/m³).
- Optionally add the fine aggregate (sand) and coarse aggregate contents to get the total batch mass and aggregate-to-cement ratio.
- Read the water-cement ratio and compare it against the durability guide for your exposure class before proceeding to trial mixes.
How it works
The water-cement ratio is simply water content divided by cement content. Total batch mass adds up whichever ingredients you supply (cement + water + fine + coarse aggregate) to give the mass of one cubic metre of fresh concrete. The aggregate-to-cement ratio divides the combined aggregate mass by the cement mass. A lower w/c ratio packs less water into the paste, giving denser, stronger, more durable concrete; AS 3600 effectively limits w/c by exposure class.
Worked example
Worked example. For cement 360, water 180, sand 700 and coarse 1100 kg/m³: w/c = 180 / 360 = 0.50; total batch mass = 360 + 180 + 700 + 1100 = 2,340 kg/m³; aggregate-to-cement ratio = (700 + 1100) / 360 = 5.0. A w/c of 0.50 sits in a common workable range but should be confirmed against the required exposure class.
Common mistakes
- Treating this as a full mix design — it does not check slump, admixtures, air content, aggregate moisture or target strength, all of which need trial mixes.
- Ignoring free moisture in aggregates, which adds to the effective water and raises the true w/c above what you entered.
- Chasing workability by adding water on site, which lifts the w/c ratio and quietly cuts strength and durability.
Frequently asked questions
Why is the water-cement ratio so important?
It is the dominant factor in concrete strength and durability. Lower w/c means a denser paste with fewer capillary pores, so higher strength and better resistance to water, chlorides and freeze-thaw. AS 3600 caps w/c by exposure class for this reason.
Does the total batch mass tell me the density?
For a complete mix (cement, water and both aggregates) the total mass per cubic metre is close to the fresh density of normal-weight concrete, typically about 2,300–2,450 kg/m³. If you leave out ingredients the total is only a partial sum, not the density.
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Tip: Enter any known values to calculate the remaining results.
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