Mole Ratio Calculator
Convert moles between substances in a reaction.
Optional, for mass
Results update as you type.
How it works
Mole ratios from a balanced chemical equation let you convert the amount of one substance into the amount of another, and this calculator performs that essential stoichiometry step. You enter the known number of moles, the coefficient of that known substance, and the coefficient of the substance you want to find, plus optionally the molar mass of the unknown, and it returns the moles of the unknown, the mole ratio, and the mass if a molar mass is given. The principle is that a balanced equation's coefficients give the exact ratio in which substances react and form, so multiplying the known moles by the ratio of coefficients converts between them. For example, in a reaction where 1 mole of a reactant produces 2 moles of a product, 3 moles of the reactant yield 6 moles of product. This mole-to-mole conversion is the heart of stoichiometry, used to figure out how much product a reaction will make, how much reactant is needed, or how substances relate quantitatively. Providing the molar mass extends the answer to grams, connecting the mole world to weighable amounts. Always start from a correctly balanced equation, since the coefficients are what make the ratio valid. Enter the known moles and coefficients to find the moles of the unknown.
Moles unknown = moles known × (coefficient unknown ÷ coefficient known)
The mole ratio between two substances in a balanced equation is the ratio of their coefficients. Multiplying the known moles by the coefficient of the unknown divided by the coefficient of the known gives the moles of the unknown. Multiplying by its molar mass converts that to grams.
Source:Stoichiometry
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter known moles, coefficient of known and coefficient of unknown.
- 2
Adjust the options
Adjust molar mass of unknown if they apply — sensible defaults are already set.
- 3
Read your result
Moles of unknown updates instantly as you type — no button to press.
Frequently asked questions
What is a mole ratio?
A mole ratio is the ratio between the amounts of two substances in a balanced chemical equation, taken directly from their coefficients. For example, in 2H₂ + O₂ → 2H₂O, the mole ratio of hydrogen to water is 2 to 2, or 1 to 1. Mole ratios let you convert moles of one substance into moles of another.
How do you use mole ratios in stoichiometry?
Multiply the known number of moles by the ratio of the unknown's coefficient to the known's coefficient. This converts the amount of one substance into the amount of another involved in the reaction. It is the central step in stoichiometry, letting you calculate how much product forms or how much reactant is required from a balanced equation.
Why must the equation be balanced first?
The mole ratio comes from the coefficients of a balanced equation, which reflect the actual proportions in which substances react by the law of conservation of mass. An unbalanced equation has incorrect coefficients, so its ratios would be wrong. Always balance the equation before using coefficients as a mole ratio, or your stoichiometry result will be inaccurate.
How do I convert moles to grams?
Multiply the number of moles by the molar mass of the substance in grams per mole. This calculator does that automatically if you enter the unknown's molar mass, giving the mass in grams alongside the moles. Converting moles to grams links the mole-based reaction ratios to the actual weighable quantities you measure in the lab.
Can I use mole ratios for reactant and product?
Yes. Mole ratios work between any two substances in the equation, whether reactant-to-reactant, reactant-to-product, or product-to-product. You simply use the coefficients of the two substances of interest. This flexibility lets you answer many questions, such as how much reactant is needed for a desired product amount, all from the same balanced equation.