# Stoichiometry Calculator

Free stoichiometry calculator. Use mole ratios from balanced equations to calculate reactant or product quantities in moles and grams.

## What this calculates

Use stoichiometry to convert between moles of reactants and products in a chemical reaction. Enter the balanced equation coefficients and the known quantity to find the unknown.

## Inputs

- **Known Substance (moles)** (mol) — min 0 — The number of moles of the known substance.
- **Known Substance Coefficient** — min 1, max 20 — The stoichiometric coefficient of the known substance in the balanced equation.
- **Unknown Substance Coefficient** — min 1, max 20 — The stoichiometric coefficient of the substance you want to find.
- **Unknown Substance Molar Mass** (g/mol) — min 0 — Enter to also calculate grams of the unknown substance. Leave 0 for moles only.
- **Known Substance Molar Mass** (g/mol) — min 0 — If you have grams instead of moles, enter the molar mass to convert.

## Outputs

- **Unknown Substance (moles)** (mol) — Moles of the unknown substance calculated from the mole ratio.
- **Unknown Substance (grams)** (g) — Mass of the unknown substance (if molar mass provided).
- **Mole Ratio** — formatted as text — The mole ratio used in the calculation.
- **Calculation Steps** — formatted as text — Step-by-step calculation explanation.

## Frequently Asked Questions

**Q: What is stoichiometry?**

A: Stoichiometry is the quantitative relationship between reactants and products in a balanced chemical equation. It uses mole ratios (the coefficients in the balanced equation) to convert between amounts of different substances.

**Q: How do I find the mole ratio?**

A: The mole ratio comes from the coefficients in the balanced equation. For example, in 2H₂ + O₂ → 2H₂O, the mole ratio of H₂ to O₂ is 2:1, and H₂ to H₂O is 2:2 (or 1:1).

**Q: Why do I need a balanced equation?**

A: A balanced equation ensures the law of conservation of mass is satisfied. Without it, the mole ratios would be incorrect, leading to wrong calculations of how much product is formed or reactant is needed.

**Q: How do I convert grams to moles?**

A: Divide the mass in grams by the molar mass (g/mol) of the substance. For example, 36 g of water / 18.015 g/mol = 2.0 mol of water.

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Source: https://vastcalc.com/calculators/chemistry/stoichiometry
Category: Chemistry
Last updated: 2026-04-21