Math & Science · Guide
How to Calculate Percent Yield, Percent Recovery and Mass Percent
Three chemistry formulas, one idea: the part divided by the whole, times 100.
Want the answer for your own numbers? Use the free Percentage Calculator — it does every step below for you.
Percent yield
Percent yield compares how much product you actually made with the most you could have made.
Percent yield = actual yield ÷ theoretical yield × 100
Finding the theoretical yield
- Write the balanced equation.
- Convert the mass of the limiting reactant to moles (divide by its molar mass).
- Use the mole ratio to find moles of product.
- Convert back to grams (multiply by the product's molar mass).
Example: heating limestone
CaCO3 → CaO + CO2. You heat 10.0 g of CaCO3 and collect 4.90 g of CaO.
Moles of CaCO3: 10.0 ÷ 100.09 = 0.0999 mol. The ratio is 1:1, so 0.0999 mol of CaO.
Theoretical yield: 0.0999 × 56.08 = 5.60 g.
Percent yield = 4.90 ÷ 5.60 × 100 = 87.5%
Need molar masses? The molar mass calculator gives them for any formula.
When two reactants are involved: the limiting reactant
With more than one starting material, the theoretical yield comes from whichever one runs out first — the limiting reactant.
2H2 + O2 → 2H2O, with 4.0 g H2 and 16.0 g O2
Moles: H2 = 4.0 ÷ 2.016 = 1.98 mol. O2 = 16.0 ÷ 32.00 = 0.500 mol.
The equation needs 2 mol H2 per mol O2. So 0.500 mol O2 uses only 1.00 mol H2. Oxygen runs out first: it is limiting.
Water formed: 0.500 × 2 = 1.00 mol × 18.02 = 18.02 g theoretical yield.
If you collect 15.5 g: 15.5 ÷ 18.02 × 100 = 86.0%
Basing the yield on the wrong reactant is the most common mistake. Always compare the mole amounts against the ratio in the equation first.
Why yields fall short — or go over 100%
- Below 100%: incomplete reactions, side reactions, product lost during transfer or filtering.
- Above 100%: almost always a sign of impurity — often the product is still wet with solvent or water. Dry it and weigh again.
Percent recovery
Percent recovery measures how much of a substance you got back after a purification step, such as recrystallisation.
Percent recovery = mass recovered ÷ starting mass × 100
Example
You start with 5.00 g of impure benzoic acid and recover 3.85 g of pure crystals.
Percent recovery = 3.85 ÷ 5.00 × 100 = 77.0%
Percent recovery is not the same as percent yield: no reaction happened, so there is no theoretical yield. Some loss is normal, because a little of the compound always stays dissolved in the cold solvent.
Mass percent (percent by mass)
Mass percent tells you how much of a mixture or compound is one component.
Mass percent = mass of component ÷ total mass × 100
Example 1: a salt solution
25 g of salt dissolved in 200 g of water. Total mass: 225 g.
Mass percent = 25 ÷ 225 × 100 = 11.1%
A common slip is dividing by the water alone (200 g). Always divide by the total.
Example 2: an element in a compound
Water, H2O: 2 × 1.008 = 2.016 for hydrogen; molar mass 18.015.
Hydrogen = 2.016 ÷ 18.015 × 100 = 11.2%; oxygen = 88.8%
All three side by side
| Measure | Top of the fraction | Bottom of the fraction |
|---|---|---|
| Percent yield | Actual product mass | Theoretical product mass |
| Percent recovery | Mass recovered | Starting mass |
| Mass percent | Mass of one component | Total mass |
The last step is always the same: divide and multiply by 100. Use the "X is what percent of Y?" mode in the percentage calculator to check your answers.
Two related measures
Percent purity
Percent purity = mass of pure substance ÷ mass of sample × 100
A 12.0 g sample that contains 10.8 g of the pure compound is 90% pure.
Atom economy
Atom economy asks how much of the starting material ends up in the product you want, assuming a perfect reaction:
Atom economy = molar mass of desired product ÷ total molar mass of reactants × 100
For CaCO3 → CaO + CO2: 56.08 ÷ 100.09 × 100 = 56.0%. Even at a 100% yield, 44% of the mass leaves as carbon dioxide. Green chemistry favours reactions with high atom economy because they make less waste.
Frequently asked questions
Percent yield = actual yield ÷ theoretical yield × 100. If you could make 5.60 g of product but collect 4.90 g, the percent yield is 87.5%.
Percent recovery = mass of pure substance recovered ÷ mass you started with × 100. Recovering 3.85 g from 5.00 g gives 77.0%.
Divide the mass of the component by the total mass of the mixture or compound, then multiply by 100. 25 g of salt in 225 g of solution is 11.1% by mass.
Convert each reactant to moles, then divide each by its coefficient in the balanced equation. The smallest result is the limiting reactant, and it sets the theoretical yield.
Percent yield compares what you actually made with what was possible. Atom economy is fixed by the equation itself: the share of reactant mass that can end up in the desired product. A reaction can have a high yield but poor atom economy.