What a stoichiometry calculator needs
Enter coefficients for reactants and products, input quantities for reactants, and, when needed, molar masses and yield information.
Stoichiometry Calculator (Limiting Reagent, Theoretical Yield, Percent Yield)
Calculate the limiting reagent, excess amount, theoretical yield, and percent yield from reaction coefficients and input quantities such as g, mol, and solution M×L.
Uses user-entered coefficients to reduce ambiguity
Works with g, mol, and solution M×L inputs
Shows excess amount, theoretical yield, and percent yield together
Supports share URLs and local auto-save
Choose an example and the same setup will be loaded when you open the tool.
Current example
Choose an example to preview the reaction and the sample quantities here.
What stoichiometry calculation means (limiting reagent, theoretical yield, and percent yield)
Stoichiometry is the quantitative relationship between reaction coefficients and actual input amounts. It tells you which reactant runs out first, how much product can form, and how an actual result compares with the theoretical maximum.
The core of a limiting reagent calculation
Divide each reactant amount in mol by its coefficient. The smallest value determines the limiting reagent.
How to read percent yield
Theoretical yield is the ideal maximum with no loss or side reaction. Percent yield compares the actual amount with that theoretical value.
How to use
- Load an example or enter the reactant and product coefficients, names, and any molar masses you need.
- For each reactant, enter the amount as mass, amount of substance, or solution input (M×L).
- If needed, choose a target product and enter expected yield or actual yield.
- Run the calculation to review the limiting reagent, excess amount, theoretical yield, yield values, and the calculation details.
Examples
Water formation
Input
2 H2 + O2 → 2 H2O, H2 4 g, O2 32 g
Output
H2 is limiting and the theoretical yield of H2O is about 35.7 g
Ammonia synthesis
Input
N2 + 3 H2 → 2 NH3, N2 28 g, H2 6 g
Output
H2 is limiting and the tool shows both the theoretical NH3 yield and the excess N2
Abstract ratio example
Input
A + 2 B → C, A 1 mol, B 1 mol
Output
B is limiting and C is 0.5 mol
How the limiting reagent is calculated (with example input)
How to read a limiting reagent calculation
The calculator divides each reactant amount in mol by the corresponding coefficient. The smallest result is used to identify the limiting reagent. When differences are extremely small, the tool also warns about a possible co-limiting case.
How percent yield is calculated (expected yield and actual yield)
A common point of confusion in yield calculations
Expected yield is a planning estimate. Actual yield is an observed result after the reaction or process. This tool keeps them separate so they are not mixed together.
Frequently asked questions
Can this tool balance a chemical equation automatically?
Not at this time. The tool is limited to user-entered coefficients so the quantitative assumptions stay explicit.
Can it calculate from solution input (M×L)?
Yes. The calculator converts concentration and volume into mol before applying the reaction ratio.
Can I use it for multistep reactions?
For now, calculate each step separately. A linked step workflow may be added later.
Which product does the yield refer to when there are multiple products?
Yield is normally reported for a chosen target product. This tool lets you select that product.
How do I handle reagent purity or assay value?
Enter purity as a percentage and the calculator will adjust the effective input mol accordingly.
Glossary
Limiting reagent
The reactant that runs out first and therefore limits the extent of reaction.
Theoretical yield
The maximum amount predicted when no side reaction or process loss occurs.
Percent yield
The actual yield divided by the theoretical yield, expressed as a percentage.
Extent of reaction ξ
A quantity that describes how far the reaction proceeds and connects coefficients to mol calculations.
Formulas
Mass to mol: n = m / MSolution to mol: n = C × VLimiting reagent: ξ = min(n_i / ν_i)Product amount: n_product = ν_product × ξPercent yield: actual / theoretical × 100
Notes
- Any mistake in molar mass, coefficient, or purity feeds directly into the result.
- The remaining solution volume is shown as supply-equivalent volume, not as the true remaining mixed solution volume.
- Substance names are included in the share URL, so do not enter confidential names.