Molar Ratio Calculator
Use balanced equation coefficients to convert an amount of one substance into the corresponding amount of another.
01 Set up your calculation
- Balance the reaction before using its coefficients.
- Enter the coefficients for the starting substance A and desired substance B.
- Enter the amount of A and read the stoichiometrically corresponding amount of B.
02 The relationship
For the assumptions behind these results, read the explanation below. You can also explore Theoretical Yield and Grams to Moles.
Follow the numbers
If 2 mol of A correspond to 3 mol of B, then 4 mol of A correspond to 4 × 3/2 = 6 mol of B.
03 Coefficients connect particles and moles
A balanced reaction encodes relative amounts. Scaling every coefficient by the same positive number leaves the molar ratio unchanged. Coefficients can relate two reactants, two products, or a reactant and product; the meaning depends on which substances you select.
The ratio is a mole ratio, not generally a mass ratio. To start with grams, divide by the molar mass first. To report the result in grams, multiply the resulting moles by the other substance’s molar mass.
04 Stoichiometry is not a guarantee of recovery
The output assumes that the selected amount participates in the stated balanced reaction. It does not determine whether another reactant runs out first or whether a competing reaction occurs.
For a product prediction, establish the limiting reagent before applying this conversion. For ideal gases at the same temperature and pressure, volume ratios can equal mole ratios, but this shortcut is not valid for arbitrary liquids and solids.
Questions from the notebook
Should I enter subscripts from a formula?
No. Use coefficients in front of whole species, such as the 2 in 2H₂, not the 2 within H₂.
Must the coefficients be integers?
Any positive equivalent scale gives the same ratio, including fractions from an otherwise balanced equation.
Does this balance a reaction?
No. It converts amounts using the balanced coefficients you provide.
References & reading
- OpenStax, Rice University — Reaction Stoichiometry ↗
Derives mole relationships from balanced reaction coefficients and converts between moles and mass.
- NIST — Guide to SI conversion factors ↗
Supports physical unit conversions. Input values are converted to the formula’s base units before calculation.
Our explanations are written for ChemistryCalc. Read how we build and check our tools. These calculations are educational estimates where the underlying model requires assumptions.