Cement-Water Mix Ratio Calculator

How much water to add to a bag of cement for a target water-cement ratio (and matching aggregate volumes for a 1:2:3 mix).

Result

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How to use this calculator

Enter the cement weight (a Portland cement bag is 94 lb).
Pick a w/c ratio — lower = stronger.
Read the gallons of water and matching aggregate volumes for a 1:2:3 mix.

About this calculator

The water-cement (w/c) ratio is the single most important variable in concrete strength. Lower w/c gives stronger, more durable concrete; higher w/c is easier to work but weaker. 0.45 is the upper limit for structural concrete; 0.55-0.6 is typical for non-structural pours. The 1:2:3 cement:sand:stone proportion (by volume) gives roughly 3,000 PSI standard concrete.

Frequently asked

What does "1:2:3 mix" mean?+

One part cement, two parts sand, three parts coarse aggregate (stone) — measured by volume. It produces roughly 3,000 PSI concrete suitable for most non-structural residential work.

How low can the w/c ratio go?+

About 0.30 with super-plasticizers — below that the mix has no workability. Above 0.65 the concrete is weak and prone to bleeding.

Why does adding more water make weaker concrete?+

Excess water leaves voids when it evaporates, reducing density and strength. Every extra gallon of water above the design w/c can drop strength 200+ PSI.

What is the difference between cement and concrete?+

Cement is the binder powder. Concrete is cement + water + sand + stone. The terms are often used interchangeably but they're not the same thing.

Should I add admixtures?+

For DIY pours, no. For freeze-thaw climates, professionals use air-entraining admixtures. For long pours, a retarder slows set time.