Work out water cement ratio instantly with clear inputs, formula shown and shareable results.
Water-cement ratio is the mass of free water divided by the mass of cement, and it governs strength and durability more than any other mix variable. Bolomey's relation, fc = K x (C/W - 0.5) with K around 22 for ordinary Portland cement, shows why: strength climbs steeply as the ratio falls.
Water-cement ratio
w/c = water kg / cement kg (1 litre of water = 1 kg)
Bolomey strength
fc = 22 x (cement/water - 0.5) MPa
Preliminary estimate only. Mix design and strength verification must follow the applicable concrete standard with trial mixes and cube testing.
w/c = water kg / cement kg (1 litre of water = 1 kg). Water-cement ratio is the mass of free water divided by the mass of cement, and it governs strength and durability more than any other mix variable.
Yes. Free water on wet sand is part of the mix water. Ignoring it is the most common reason site concrete has a higher ratio than the design assumed.
This calculator takes 3 inputs: Cement content, Water added, Target water-cement ratio. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.