The use of water reducing agent can improve the strength and state of concrete. The purpose of water reducer is to reduce water consumption. The strength of concrete generally adopts the theory of water-cement ratio. Theoretically, if the water-cement ratio is 0.6, then if the water consumption of your admixture is 20Kg, it can be regarded as saving cement by 20/0.6 = 33kg. Considering all kinds of factors, it is generally believed that how much water is reduced is equivalent to how much cement is saved.

The water reducing rate of each water reducer is different, and the specific value can't be given to you. In addition, concrete is generally calculated in cubic meters, so it is easy to talk about weight. I hope I have solved your problem.