Molar Ratio Calculator
Use balanced-equation coefficients to convert from a known reactant/product amount to another substance amount.
What is a molar ratio?
A molar ratio is the proportional relationship between substances in a balanced chemical equation. The coefficients in front of each chemical formula tell you how many moles of one substance react with or produce moles of another.
For example, in the reaction:
N₂ + 3H₂ → 2NH₃
The molar ratio of hydrogen to ammonia is 3:2. That means every 3 moles of H₂ can produce 2 moles of NH₃ (assuming complete reaction and no limiting side effects).
How this molar ratio calculator works
This calculator follows standard stoichiometry steps:
- Convert your known amount to moles (if needed).
- Apply the mole ratio from equation coefficients.
- Convert target moles to grams if you selected mass output.
The core formula is:
Target moles = Known moles × (Target coefficient / Known coefficient)
Step-by-step usage
1) Enter the known side
Input the coefficient of the known compound and the amount you currently have. Choose whether that amount is in moles or grams.
2) Add molar mass when using grams
If your known amount is in grams, provide its molar mass (g/mol) so the calculator can convert grams to moles accurately.
3) Enter the target side
Input the coefficient for the substance you want to find. Then choose whether you want the result in moles or grams.
4) Click calculate
You’ll get the mole ratio used, converted known moles, computed target moles, and final target amount.
Worked example
Reaction: 2H₂ + O₂ → 2H₂O
- Known: 10 g of H₂
- Known coefficient: 2
- Target: H₂O (coefficient 2), output in grams
- Molar masses: H₂ = 2.016 g/mol, H₂O = 18.015 g/mol
Since coefficients are 2 and 2, the mole ratio is 1:1. So moles of water formed equal moles of hydrogen consumed. The calculator automates this and gives final grams of H₂O.
Common stoichiometry mistakes to avoid
- Using an unbalanced equation.
- Mixing grams and moles without conversion.
- Entering molecular weight in wrong units.
- Confusing coefficient values with subscripts in formulas.
Why molar ratios matter
Molar ratio calculations are essential in lab synthesis, chemical manufacturing, environmental chemistry, pharmaceuticals, and engineering process design. They help you estimate reactant requirements, theoretical yield, and material efficiency before running an experiment or production batch.
Final note
This tool gives stoichiometric results based on ideal balanced-equation math. Real reactions can differ due to limiting reagents, incomplete conversion, impurities, and side reactions, so treat results as theoretical unless verified experimentally.