Percent yield calculator

A percent yield calculator compares the mass of product you actually made with the most you could have made. Percent yield = actual yield ÷ theoretical yield × 100. Our Stoichiometry Calculator works out the theoretical yield from the balanced equation and your reactant amounts, then gives the percent yield as soon as you type the mass you collected.

Percent yield is one of the results of the Stoichiometry Calculator, so there is nothing to switch on: fill in the Actual mass collected box and the percentage appears. It is called percentage yield in the UK.

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Stoichiometry Calculator

Find reacting masses, limiting reactants, yield and atom economy

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How to use the percent yield calculator

1. In Reaction, type the equation, such as Mg + O2 -> MgO. It does not need to be balanced: the calculator balances it for you.
2. In Amounts, type how much of each reactant you started with, in grams or moles. Leave a reactant blank if it was in excess.
3. In Product, choose the product you collected.
4. Type its mass in Actual mass collected, in grams.
5. Read the results: the limiting reactant, the theoretical yield, the percentage yield and the atom economy, with each step of the working.

The working balances the equation, finds the moles of each reactant, finds which runs out first, uses the mole ratio, and converts to a mass. Under the equation box, four example reactions are ready to load with one click, including iron from its ore and making ammonia.

The percent yield formula

The actual yield is the mass of product you really collected. The theoretical yield is the mass you would get if every bit of the limiting reactant turned into product, worked out from the balanced equation. Rearranged, actual yield = percent yield × theoretical yield ÷ 100, which tells you how much to expect.

How to find the theoretical yield

1. Balance the equation.
2. Turn each reactant mass into moles: moles = mass ÷ molar mass.
3. Find the limiting reactant: divide each reactant's moles by its number in the equation. The smallest runs out first.
4. Use the mole ratio to find the moles of product.
5. Turn the moles of product into a mass: mass = moles × molar mass.

Worked examples you can check in the calculator

Example 1: burning magnesium

4.8 g of magnesium is burned in plenty of oxygen and 7.2 g of magnesium oxide is collected. Find the percent yield. The balanced equation is 2Mg + O₂ → 2MgO, so 1 mol of Mg makes 1 mol of MgO.

In the calculator, type Mg + O2 -> MgO, put 4.8 g for Mg, leave O2 blank because it was in excess, and type 7.2 for the actual mass. It gives a theoretical yield of 7.96 g and a percentage yield of 90.46%.

Example 2: a limiting reactant

14 g of nitrogen reacts with 6 g of hydrogen to make ammonia, and 5.1 g of ammonia is collected. N₂ + 3H₂ → 2NH₃.

• Moles: N₂ = 14 ÷ 28.014 = 0.4998 mol, and H₂ = 6 ÷ 2.016 = 2.976 mol.
• Divide by the numbers in the equation: N₂ gives 0.4998 ÷ 1 = 0.4998, and H₂ gives 2.976 ÷ 3 = 0.992. Nitrogen is smaller, so it is the limiting reactant.
• Ammonia made: 2 × 0.4998 = 0.9995 mol, which is 0.9995 × 17.031 = 17.02 g.
• Percent yield: 5.1 ÷ 17.02 × 100 = 30.0%.

Type both amounts into the calculator and it names N₂ as the limiting reactant and gives the same 17.02 g and 29.96%. Making ammonia is a reversible reaction, so a low yield like this is expected.

Example 3: heating limestone

20 g of calcium carbonate is heated: CaCO₃ → CaO + CO₂. The theoretical yield of calcium oxide is 11.21 g. If 9.5 g is collected, the percent yield is 9.5 ÷ 11.21 × 100 = 84.8%. In the calculator, choose CaO as the product. Its atom economy for CaO is 56.0%, because the carbon dioxide is wasted.

Why is the percent yield less than 100%?

• The reaction is reversible, so it never goes to completion, as in making ammonia.
• Side reactions turn some reactant into other products.
• Product is lost when it is filtered, transferred between containers or purified.
• The reaction is incomplete, for example because it was stopped too soon or not heated enough.

A percent yield over 100% means something went wrong: usually the product is still wet or contains impurities, so it weighs more than the pure product could. Percent yield is not the same as atom economy, which measures how much of the reactants' mass ends up in the wanted product even with a perfect yield. Our atom economy guide covers that, and the stoichiometry calculator guide covers limiting reactants and reacting masses in full.

Common mistakes

• Dividing the wrong way round. It is actual over theoretical. A yield over 100% usually means the division is upside down.
• Skipping the balanced equation. The mole ratio comes from the balancing numbers, so an unbalanced equation gives the wrong theoretical yield.
• Using the reactant in excess. The theoretical yield always comes from the limiting reactant.
• Mixing grams and moles. Compare the actual and theoretical yields in the same units.
• Using the wrong molar mass. MgO is 40.30 g/mol, not 24.31 for Mg plus 16.00 for one O counted twice. Add up each atom once per formula.

Practise yield questions in a short timed paper

Percent yield comes up in Honors Chemistry and High School Chemistry practice, and in A-level Chemistry: Year 1 in the UK. Each daily paper is a short timed paper of 8 questions worth 25 to 35 marks, and the papers mix topics, so yield will not come up in every one. For the moles step on its own, use the Moles Calculator.

Read next

Chemistry · Moles and quantitiesStoichiometry calculator: limiting reactant and yieldFind the limiting reactant, theoretical yield, percentage yield and atom economy from any equation, balanced for you, with worked examples to check.