Equivalent Weight Calculator

Calculate equivalent weight, molar mass, or n-factor from any two inputs, with unit conversions for g/mol, kg/mol, mg/mol, and lb/mol.

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Equivalent Weight Formula

The following formula is used to calculate an equivalent weight (equivalent mass).

EW = M / n

• Where EW is the equivalent weight (mass per equivalent)
• M is the molar mass (molecular weight in g/mol)
• n is the n‑factor (number of equivalents per mole). In a redox reaction, n is the number of electrons transferred per formula unit in the balanced reaction.

To calculate the equivalent weight, divide the molar mass by the n‑factor.

Equivalent Weight Definition

Equivalent weight (also called equivalent mass) is the mass of a substance that corresponds to 1 equivalent of reaction. It can be defined as the molar mass divided by the n‑factor, where the n‑factor depends on the reaction context (for example, moles of H⁺ or OH⁻ exchanged in acid–base chemistry, or moles of electrons transferred in a balanced redox reaction). Historically, it was described as the mass that combines with or displaces 1.008 g of hydrogen (or 8.00 g of oxygen, 35.45 g of chlorine).

What are the units for equivalent weight?

Equivalent weight is typically expressed as a mass per equivalent, such as g/eq (grams per equivalent). Any mass-per-equivalent unit can be used (for example, kg/eq, mg/eq, or lb/eq), as long as you are consistent.

Is equivalent weight and equivalent mass the same?

In chemistry, “equivalent weight” and “equivalent mass” are generally used interchangeably. Despite the word “weight,” the quantity refers to a mass corresponding to 1 equivalent (not the physics definition of weight as a gravitational force).

Equivalent Weight Example

FAQ