Equivalent weight in chemistry is also known as gram equivalent. It is the mass of a given substance which will combine with or displace a fixed quantity of another substance.

The equivalent weight of an element is the mass which combines with or displaces 1.008 gram of hydrogen or 8.0 grams of oxygen or 35.5 grams of chlorine. These values are the atomic weight divided by the usual valence. For oxygen, as an example, that is 16.0g / 2.