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
Water needed
5.64 gallons
47.0 lb of water at 0.5 w/c ratio.
- Cement94 lb (1.00 ft³)
- Sand (2:1 ratio)2.00 ft³
- Stone (3:1 ratio)3.00 ft³
- Resulting mix volume~67% of dry volumes due to packing.4.02 ft³
Step-by-step
- Water by weight = cement × w/c = 94 × 0.5 = 47.0 lb.
- Convert to gallons: 47.0 ÷ 8.34 = 5.64 gal.
- For a 1:2:3 mix by volume, use 2.00 ft³ sand and 3.00 ft³ stone.
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
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.
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