Stoichiometry Calculator (Moles to Moles)
Use coefficients from a balanced chemical equation to convert moles of one substance into moles of another.
What this moles to moles calculator does
A moles-to-moles conversion is one of the most common tasks in chemistry. This calculator handles the stoichiometry step: it uses the coefficient ratio from your balanced equation to convert a known number of moles into the moles of a different substance in the same reaction.
In other words, this tool answers questions like: “If I have 3.2 mol of reactant A, how many moles of product B can form?”
How moles-to-moles conversion works
1) Start with a balanced equation
Coefficients from a balanced equation represent mole ratios. For example:
This means 2 moles of hydrogen react with 1 mole of oxygen to make 2 moles of water.
2) Use the coefficient ratio as a conversion factor
The calculator applies this exact formula and gives you the target moles instantly.
3) Keep units as moles
In this specific conversion, units stay in moles throughout. If you need grams or particles, do a second step after this conversion.
How to use this calculator
- Enter the known amount in moles.
- Enter the coefficient of the known substance from your balanced equation.
- Enter the coefficient of the target substance.
- Optionally add substance labels (like CO2, NH3) to make the result easier to read.
- Click Calculate.
Worked examples
Example 1: Oxygen to water
Equation: 2H2 + O2 → 2H2O
Known: 3.5 mol O2
Coefficients: O2 = 1, H2O = 2
Calculation: 3.5 × (2/1) = 7.0 mol H2O
Example 2: Hydrogen to ammonia
Equation: N2 + 3H2 → 2NH3
Known: 4.2 mol H2
Coefficients: H2 = 3, NH3 = 2
Calculation: 4.2 × (2/3) = 2.8 mol NH3
Common coefficient ratios at a glance
| Balanced Reaction | Known → Target | Mole Ratio |
|---|---|---|
| 2H2 + O2 → 2H2O | O2 → H2O | 2 : 1 |
| N2 + 3H2 → 2NH3 | H2 → NH3 | 2 : 3 |
| CH4 + 2O2 → CO2 + 2H2O | CH4 → CO2 | 1 : 1 |
Common mistakes to avoid
- Using an unbalanced equation: always balance first.
- Flipping the ratio: use target coefficient over known coefficient.
- Mixing grams and moles: convert grams to moles first if needed.
- Rounding too early: keep extra digits until your final step.
FAQ
Can I use decimals for coefficients?
You can enter them, but standard balanced equations usually use whole numbers. If you used fractional balancing temporarily, convert to whole-number coefficients when possible.
Does this calculator account for limiting reagent?
No. This tool performs a direct mole-ratio conversion. If multiple reactants are given, you must determine the limiting reagent first.
What if I start with grams, not moles?
Convert grams to moles using molar mass, run the moles-to-moles conversion, then convert back to grams if needed.
Final thoughts
Stoichiometry becomes much easier when you separate it into clear steps: balance the equation, apply the mole ratio, and keep your units organized. This calculator handles the ratio step quickly and cleanly so you can focus on chemistry instead of calculator errors.