[mike97]

From a quick Google search: 1m3 of concrete = 150l water + 250kg cement + 700kg sand + 1200kg aggregates.

Even if you used just cement and water I think you would get more than 12L from 25kg.

[xxs]

True, I meant pre-mixed bag of cement + sand.

>Even if you used just cement and water I think you would get more than 12L from 25kg.

The thing will crack very soon. The density of concrete is around 2.4g/cm3