About the Theoretical Yield Calculator
This theoretical yield calculator works out the maximum mass of product a reaction can make, based on the mass of the limiting reactant and the balanced chemical equation. Enter the reactant’s mass and molar mass, the stoichiometric coefficients of the reactant and the product, and the product’s molar mass. The calculator converts grams to moles, applies the mole ratio and converts back to grams.
It is designed for chemistry students checking stoichiometry homework and lab reports, and for anyone running a synthesis who wants to know what a 100% yield would look like. If you also enter the actual mass you recovered, it reports the percent yield.
Use the limiting reactant — the one that runs out first. If you are not sure which reactant is limiting, check with the limiting reactant calculator first. Molar masses are in g/mol and masses in grams.
With the default inputs, the theoretical yield is 2.6087 g. Change any value above to recalculate instantly.
How to use the theoretical yield calculator
- 1Balance the chemical equation and identify the limiting reactant.
- 2Enter the mass and molar mass of the limiting reactant.
- 3Enter the coefficients of the reactant and the product from the equation.
- 4Enter the molar mass of the product.
- 5Optionally enter your actual yield to get the percent yield.
Formula and method
Stoichiometry always goes through moles. First divide the mass of the limiting reactant by its molar mass to get moles. Then multiply by the mole ratio from the balanced equation — the product coefficient b divided by the reactant coefficient a — to get moles of product. Finally multiply by the product’s molar mass to get grams.
The result is the maximum possible mass assuming the reaction goes to completion with no side reactions or losses. Real experiments recover less, and the percent yield compares what you actually isolated with this theoretical maximum.
- m_reactant
- Mass of the limiting reactant (g)
- M
- Molar mass (g/mol)
- a, b
- Coefficients of reactant and product in the balanced equation
Worked examples
Aspirin from 2.00 g of salicylic acid
2.00 g ÷ 138.12 g/mol = 0.01448 mol of salicylic acid. The 1:1 ratio gives 0.01448 mol of aspirin, × 180.158 g/mol = 2.609 g theoretical. Recovering 2.2 g is an 84.3% yield.
Water from 10 g of hydrogen (2H₂ + O₂ → 2H₂O)
10 g ÷ 2.016 g/mol = 4.960 mol H₂. The 2:2 ratio gives 4.960 mol H₂O, × 18.015 g/mol = 89.36 g of water if oxygen is in excess.
Iron from 100 g of iron(III) oxide (Fe₂O₃ + 3CO → 2Fe + 3CO₂)
100 g ÷ 159.69 g/mol = 0.6262 mol Fe₂O₃. Each mole makes 2 mol of iron, so 1.2524 mol Fe × 55.845 g/mol = 69.94 g of iron at most.
Frequently asked questions
How do you calculate theoretical yield?+
Convert the mass of the limiting reactant to moles, multiply by the mole ratio of product to reactant from the balanced equation, then multiply by the product’s molar mass to get grams.
What is the difference between theoretical and actual yield?+
Theoretical yield is the maximum product possible if every molecule of limiting reactant reacts perfectly. Actual yield is what you really isolate in the lab, which is almost always lower because of losses and side reactions.
How do I calculate percent yield?+
Divide the actual yield by the theoretical yield and multiply by 100. For example, 2.2 g recovered from a theoretical 2.61 g is an 84.3% yield.
Why must I use the limiting reactant?+
The limiting reactant is used up first and stops the reaction, so it determines how much product can form. Using a reactant that is in excess would overestimate the yield.
Can percent yield be over 100%?+
Not in reality. A result above 100% usually means the product is still wet with solvent, contains impurities or unreacted starting material, or there was a weighing error.