Stoichiometry Calculator
Type a chemical equation, give the amount of one or more reactants, and instantly see the balanced equation, the limiting reactant, the theoretical yield of each product (in moles and grams), the leftover excess reactant, and — if you enter an actual yield — the percent yield. Every amount can be grams, moles, or a solution given as molarity × volume.
Chemical equation
Reactant amounts
Leave a reactant blank to treat it as unspecified — it won't be used to find the limiting reactant.
Results
The limiting reactant runs out first. Its moles ÷ coefficient gives the reaction extent ξ; each product's yield is ξ × its coefficient, and each reactant consumed is ξ × its coefficient.
Amounts update the results live. Use grams, moles, or a solution's molarity × volume for each reactant.
About the Stoichiometry Calculator
Stoichiometry is the heart of quantitative chemistry: it uses the whole-number ratios in a balanced equation to relate the amounts of reactants and products. This calculator does the whole workflow in one place. First it balances the equation you type, using exact arithmetic so the coefficients are always the smallest correct integers. Then, from the amount you give for each reactant — in grams, in moles, or as a solution's molarity multiplied by its volume — it converts everything to moles and finds the limiting reactant, the one that runs out first and therefore caps how much product can form. It reports the reaction extent ξ (how many "units" of the reaction occur), the theoretical yield of every product in both moles and grams, and how much of each excess reactant is left over once the limiting one is used up. Finally, if you weigh your real product and enter that actual yield, it computes the percent yield so you can judge how efficient your reaction was. It's ideal for chemistry homework, lab pre-work and report checking, and for understanding why a reaction stops where it does.
How to use this calculator
- 1 Type a chemical equation (or tap an example) — it is balanced automatically and shown with its coefficients.
- 2 For each reactant, choose grams, moles, or solution (molarity × volume) and enter the amount; leave a reactant blank to skip it.
- 3 Read the limiting reactant, the theoretical yield of each product in moles and grams, and the leftover excess — then enter an actual yield to get the percent yield.
How stoichiometry works
Every balanced equation is a recipe written in mole ratios. The steps are: 1. Balance the equation so atoms are conserved (e.g. N2 + 3 H2 → 2 NH3). 2. Convert each given amount to moles. Grams become moles by dividing by the molar mass; a solution becomes moles by multiplying molarity (mol/L) by volume (L); moles are used as-is. 3. For each supplied reactant, divide its moles by its coefficient. The smallest of these ratios is the reaction extent ξ, and the reactant that produced it is the limiting reactant — it runs out first. 4. Multiply ξ by each product's coefficient to get the theoretical yield in moles, then by the product's molar mass to get grams. 5. For every other reactant, the amount consumed is ξ × its coefficient; whatever is left over is the excess. For example, mixing 4 g of H2 with 32 g of O2 in 2 H2 + O2 → 2 H2O gives H2 = 1.984 mol (÷2 = 0.992) and O2 = 1 mol (÷1 = 1), so H2 is limiting, ξ ≈ 0.992, and about 1.98 mol (≈ 35.7 g) of water forms with a little O2 left over.
Frequently asked questions
What is the limiting reactant?
The limiting reactant is the reactant that is completely used up first, which caps how much product can form. To find it, convert every reactant to moles and divide by its coefficient in the balanced equation; the reactant with the smallest result is limiting. The others are in excess, meaning some is left over after the reaction stops. This calculator highlights the limiting reactant automatically and shows how much of each excess reactant remains.
How do I calculate theoretical yield?
Theoretical yield is the maximum amount of product a reaction can make, set by the limiting reactant. Find the reaction extent ξ (the limiting reactant's moles divided by its coefficient), then multiply ξ by the product's coefficient to get moles of product, and by the product's molar mass to get grams. This calculator reports the theoretical yield of every product in both moles and grams at once.
What is the difference between theoretical and percent yield?
Theoretical yield is the maximum product predicted by the balanced equation and the limiting reactant — what you'd get if the reaction were perfect. Percent yield compares what you actually obtained to that maximum: percent yield = actual ÷ theoretical × 100. A high percent yield means an efficient reaction. Yields above 100% are possible when the product is impure or still wet, so the value is not capped here.
Can I use molarity and volume instead of grams?
Yes. Choose "Solution (M × L)" for any reactant and enter its molarity in mol/L and its volume in litres; the moles are molarity × volume. You can mix modes freely — for instance, one reactant in grams and another as a solution. The calculator converts everything to moles before finding the limiting reactant and the yields.
Related tools
Round out your chemistry workflow on UnitConv: balance any reaction with the chemical equation balancer, find any compound's molar mass with the molar mass calculator, and judge reaction efficiency with the percent error & percent yield calculator.