Equivalent Weight Calculator
Find the equivalent weight (gram-equivalent) of a compound.
Result
How it is calculated
Equivalent weight is the mass that supplies one equivalent of reacting species: E = M / n, where M is the molar mass in g/mol and n is the valence factor (number of H⁺ or OH⁻ exchanged, or electrons transferred per formula unit). The result is in g/eq and is shown with four decimals. Both inputs must be greater than zero, otherwise the tool returns nothing. The valence is not a property you can read from the formula alone: it depends on the reaction. Sulfuric acid has n = 2 when it gives up both protons, but n = 1 if only one proton reacts, and a redox agent's n depends on the electrons it exchanges.
Worked example
For sulfuric acid, H₂SO₄, the molar mass is 98.08 g/mol and both hydrogens are replaced in a full neutralisation, so n = 2. Then E = 98.08 / 2 = 49.04. The tool displays 49.0400 g/eq. This means 49.04 g of sulfuric acid supplies one mole of H⁺, and it is the figure you would use to prepare a 1 N solution (49.04 g per litre of solution).
Common mistakes
- Using the wrong valence for the reaction: n is set by what actually reacts, not simply by the number of hydrogens in the formula.
- Entering molar mass in kg/mol or using an outdated mass; the tool expects g/mol.
- Mixing equivalent weight with molar mass: for monoprotic acids they match, but for H₂SO₄ they differ by a factor of two.
- Entering n = 0 or a negative number, which is rejected.
About this calculator
The equivalent weight of a substance is its molar mass divided by its valence factor (n-factor) — the number of replaceable H⁺ ions for an acid, OH⁻ ions for a base, or the number of electrons transferred for a redox reagent. It represents the mass of a substance that supplies or reacts with exactly one mole of “reacting unit” (one proton, one hydroxide, or one electron).
It's the basis of normality (N = molarity × n-factor), still widely used in acid-base and redox titrations because equivalents react in exact 1:1 ratios regardless of the compound's stoichiometry. Chemistry students and laboratory technicians use equivalent weight to prepare normal solutions and calculate titration endpoints, especially for polyprotic acids and multivalent redox reagents where molarity alone can be misleading. Enter the molar mass and valence to get the equivalent weight.
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