Abrams' law (also called Abrams' water-cement ratio law)^[1] is a concept in civil engineering. The law states the strength of a concrete mix is inversely related to the mass ratio of water to cement.^[1][2] As the water content increases, the strength of concrete decreases.

Abrams’ law is a special case of a general rule formulated empirically by Feret:

${\displaystyle S={\frac {A}{B^{w/c}}}}$

where

S is the strength of concrete

A and B are constants and A=96 N/mm2, B=7 (this is valid for the strength of concrete at the age of 28 days)

w/c is the water–cement ratio, which varies from 0.3 to 1.20