Quick answer
Stoichiometry converts between reactants and products with mole ratios: mass B = (mass A ÷ M_A) × (coef B ÷ coef A) × M_B. For 2H₂ + O₂ → 2H₂O, 10 g of H₂ (M = 2.016) makes 4.960 mol and 89.36 g of water.
Enter the mass and molar mass of species A, the coefficients and the molar mass of B. The calculator returns the mass of B and the moles.
Related tools: Mole Calculator: Convert between mass, moles and number of particles. Percent Yield Calculator: Percent yield of a reaction. Electron Configuration Calculator: Ground-state electron configuration of an element or monatomic ion, with noble-gas shorthand and unpaired electrons.
How to use the Stoichiometry Calculator
- Enter mass of species A (g) (above 0).
- Enter molar mass of A (g/mol) (above 0).
- Enter coefficient of A (above 0).
- Enter coefficient of B (above 0).
- Enter molar mass of B (g/mol) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Mass of species A | A number, in g | > 0 |
| Molar mass of A | A number, in g/mol | > 0 |
| Coefficient of A | A number | > 0 |
| Coefficient of B | A number | > 0 |
| Molar mass of B | A number, in g/mol | > 0 |
Formula and method
Formula
mass B = (mass A ÷ M_A) × (coef B ÷ coef A) × M_B
IEEE-754 double precision; shown to the decimals indicated.
Assumes A is the limiting reagent and the reaction goes to completion.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Mass of species A = 10; Molar mass of A = 2.016; Coefficient of A = 2; Coefficient of B = 2; Molar mass of B = 18.015.
| Result | Value |
|---|---|
| Mass of species B | 89.3601 g |
| Moles of reactant | 4.960317 mol |
| Moles of product | 4.960317 mol |
Example 2
Inputs: Mass of species A = 25; Molar mass of A = 32.06; Coefficient of A = 1; Coefficient of B = 1; Molar mass of B = 98.079.
| Result | Value |
|---|---|
| Mass of species B | 76.4808 g |
| Moles of reactant | 0.779788 mol |
| Moles of product | 0.779788 mol |
Example 3
Inputs: Mass of species A = 5.5; Molar mass of A = 44.01; Coefficient of A = 1; Coefficient of B = 2; Molar mass of B = 28.01.
| Result | Value |
|---|---|
| Mass of species B | 7.0009 g |
| Moles of reactant | 0.124972 mol |
| Moles of product | 0.249943 mol |
The first line is the headline result (mass of species B). Below it the stoichiometry Calculator lists moles of reactant and moles of product, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Steps
10 ÷ 2.016 = 4.960 mol of H₂. The ratio of water to hydrogen is 2:2 = 1, so 4.960 mol of H₂O. Multiplying by 18.015 g/mol gives 89.36 g.
Balance first
The equation must be balanced, and the result assumes the reagent is limiting and the reaction goes to completion. Compare actual with theoretical yield using the Percent Yield calculator.
How the result changes with mass of species A
Holding every other input at the first worked example, this table changes only mass of species A. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Mass of species A | Mass of species B | Moles of reactant | Moles of product |
|---|---|---|---|
| 5 | 44.6801 g | 2.480159 mol | 2.480159 mol |
| 10 | 89.3601 g | 4.960317 mol | 4.960317 mol |
| 20 | 178.7202 g | 9.920635 mol | 9.920635 mol |
| 40 | 357.4405 g | 19.84127 mol | 19.84127 mol |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Mass of species A: entering "0" shows "Mass of species A must be greater than 0." beside that field and no result.
- Coefficient of A: entering "0" shows "Coefficient of A must be greater than 0." beside that field and no result.
Choosing between the Stoichiometry Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Mole Calculator](/science/mole/) | start from and molar mass | Amount |
| [Percent Yield Calculator](/science/percent-yield/) | actual yield and theoretical yield | Percent yield |
| [Electron Configuration Calculator](/science/electron-configuration/) | element and charge | Electron configuration of H |
| [Dilution Calculator](/science/dilution-ratio/) | solve for | Final volume V₂ |
| [Molarity Calculator](/science/molarity-calculator/) | solute mass, molar mass and solution volume | Molarity |
Background: chemistry calculations
Most basic chemistry calculations chain three relations: moles n = mass ÷ molar mass, molarity M = n ÷ volume in litres, and dilution C₁V₁ = C₂V₂. Keep units consistent: grams with g/mol, litres with mol/L.
Molar masses come from standard atomic weights, which differ slightly between tables and with the isotopic make-up of a real sample.
Assumptions and limitations
- Balance the equation first
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for mass of species A and coefficient of A to confirm this.
Frequently asked questions
What is a mole ratio?
The ratio of coefficients in the balanced equation.
What is a limiting reagent?
The reactant that runs out first.
How many grams of O₂ are needed?
About 79.4 g for 10 g of H₂.
What does the Stoichiometry Calculator calculate?
Mass of a product (or reactant) from the mass of another species in a balanced equation. It returns Mass of species B, Moles of reactant and Moles of product.
What formula does the Stoichiometry Calculator use?
mass B = (mass A ÷ M_A) × (coef B ÷ coef A) × M_B. Assumes A is the limiting reagent and the reaction goes to completion.
What do I need to enter in the stoichiometry Calculator?
You enter Mass of species A (g), Molar mass of A (g/mol), Coefficient of A, Coefficient of B and Molar mass of B (g/mol).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Balance the equation first.
What is an example of a stoichiometry result?
With mass of species A 10, molar mass of A 2.016, coefficient of A 2, coefficient of B 2 and molar mass of B 18.015, the mass of species B is 89.3601 g.
Where does the method come from?
The method follows: OpenStax, Chemistry 2e (Rice University).
Related calculators
- Mole Calculator — Convert between mass, moles and number of particles.
- Percent Yield Calculator — Percent yield of a reaction.
- Electron Configuration Calculator — Ground-state electron configuration of an element or monatomic ion, with noble-gas shorthand and unpaired electrons.
- Molarity Calculator — Concentration of a solution from solute mass, molar mass and volume.
- Average Atomic Mass Calculator — Weighted average of isotope masses.
Sources
- OpenStax, Chemistry 2e (Rice University)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.