Stoichiometry Calculator
Stoichiometry calculator works out Balanced equation and Stoichiometric coefficients from What to calculate, Chemical equation and Amount of each reactant. The default figures on this page give theoretical yield of 33.791667 g; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
7 steps
- Balanced equation: N2 + 3H2 → 2NH3
- Molar masses (IUPAC 2021 abridged, dataset ciaaw-2024-abridged + nist-awic-ame2020): M(N2) = 28.014 g/mol; M(H2) = 2.016 g/mol; M(NH3) = 17.031 g/mol
- Moles supplied: N2 0.9995002498750625 mol; H2 2.9761904761904763 mol
- Divide by the coefficients: N2 0.9995002498750625/1 = 0.9995002498750625; H2 2.9761904761904763/3 = 0.9920634920634921
- The smallest ratio is H2, so it is the limiting reagent and the extent of reaction is 0.9920634920634921 mol.
- n(NH3) = 2 x 0.9920634920634921 = 1.9841269841269842 mol, m = 1.9841269841269842 x 17.031 = 33.791666666666664 g.
- Left over: N2 0.0074367578115703825 mol (0.2083333333333327 g)
Stoichiometric coefficientstable
Reactantstable
| formula | coefficient | molarMass | suppliedMoles | molesPerCoefficient | consumedMoles | leftoverMoles | leftoverMass | limiting |
|---|---|---|---|---|---|---|---|---|
| N2 | 1 | 28.014 | 0.9995 | 0.9995 | 0.992063 | 0.007437 | 0.208333 | No |
| H2 | 3 | 2.016 | 2.97619 | 0.992063 | 2.97619 | 0 | 0 | Yes |
Productstable
| formula | coefficient | molarMass | moles | mass |
|---|---|---|---|---|
| NH3 | 2 | 17.031 | 1.984127 | 33.791667 |
Figures from IUPAC atomic weights, 2024 edition, checked 31 August 2026. Its 4 worked examples are re-run on every release, last on 15 September 2026. What changed · how reference data is kept current
Sources and references
3 sources
What the stoichiometry calculator calculates
Balances a chemical equation, identifies the limiting reagent from the amounts of each reactant, and reports the theoretical yield, the leftover excess reactant and the percent yield.
How to use this stoichiometry calculator
Enter What to calculate, Chemical equation, Amount of each reactant and Amounts are in. Balanced equation updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Balanced equation, Stoichiometric coefficients and Limiting reagent.
The method follows OpenStax Chemistry 2e, section 4.3 Reaction Stoichiometry, OpenStax Chemistry 2e, section 4.4 Reaction Yields and IUPAC Compendium of Chemical Terminology (Gold Book), "stoichiometric number".
Ammonia synthesis from 28.0 g N2 and 6.0 g H2 example
With Chemical equation: N2 + H2 -> NH3, Amount of each reactant: 28,6, Amounts are in: g, the calculator returns Balanced equation: N2 + 3H2 → 2NH3, Limiting reagent: H2, Theoretical yield: 1.98412698. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Balanced equation, Stoichiometric coefficients and Limiting reagent. The inputs you can vary are What to calculate, Chemical equation, Amount of each reactant, Amounts are in, Product to report (optional) and Actual yield obtained (optional).
Understanding Balanced equation, Stoichiometric coefficients and Limiting reagent
Yields assume the written reaction goes to completion with pure reactants and no competing reaction. Confirm the reaction, purity and product basis before relying on the figure for laboratory or process work.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
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Frequently asked questions
How do you calculate stoichiometry?
Balances a chemical equation, identifies the limiting reagent from the amounts of each reactant, and reports the theoretical yield, the leftover excess reactant and the percent yield. Open “How this is worked out” beside the result to see each step for your own figures.
Is stoichiometry easy or hard?
Balances a chemical equation, identifies the limiting reagent from the amounts of each reactant, and reports the theoretical yield, the leftover excess reactant and the percent yield. Put your own figures in above and the working updates beside the result. For scale, the default figures on this page give 33.791667 g.
How do you calculate stoichiometry step-by-step?
It needs What to calculate, Chemical equation, Amount of each reactant, Amounts are in, Product to report (optional) and Actual yield obtained (optional). Nothing else is required, and the figures stay in your browser.
What are the five laws of stoichiometry?
On the figures this page opens with, the theoretical yield is 33.791667 g. No single number fits everyone: it follows What to calculate, Chemical equation and Amount of each reactant, so enter your own above and the answer updates as you type.
What information do I need for the stoichiometry calculator?
You need What to calculate, Chemical equation, Amount of each reactant, Amounts are in, Product to report (optional) and Actual yield obtained (optional). The page opens with default figures that give theoretical yield of 33.791667 g, so you can see the scale before entering your own.
What does this stoichiometry calculator show?
It shows Balanced equation, Stoichiometric coefficients, Limiting reagent, Extent of reaction, Product reported, Theoretical yield, Percent yield and Reactants, with the working and any warnings for your entries.