# Definition of water cement ratio & calculation of water amount for concrete

In this construction video tutorial, the renowned engineer Sami Ullah, presents a useful video tutorial where he briefly explains the definition of water cement ratio and how the amount of water is obtained for concrete.

Water cement ratio means the proportion of weight of blending water to that of cement in the mixture.

The strength of concrete/mortar is based on the net quantity of water utilized with per bag of cement.

For full hydration, cement requires water nearly 38% by weight. As full hydration is an everlasting method and the period of concrete mixing and casting is short, the cement is amalgamated with 23% water. Because of this, the concrete may not be functional with such a low water cement ratio of 0.23.

Therefore, extra water is necessary to keep the workability. This surplus water by weight will vaporize on drying of concrete and it leads to form voids in it owning to trap of air bubbles insides.

In this way the strength of concrete will be reduced.

For nominal concrete mix that ranges from M10, M15, M20 and M25, water cement ratio will remain at 0.4 to 0.6.

The water quantity for concrete can be worked out as follow :-

Suppose water is needed for 50 kg cement i.e. one bag cement. One bag cement (50 kg) = 1.25 cft

So, total amount of water = 0.5 x 50 kg (as water cement ratio remains at 0.4 to 0.6, here 0.5 is taken) = 25 litres of water for 50 kg cement.

To get more details, go through the following video tutorial.

Video Source: Sami Ullah Stanikzai