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Percent Yield Calculator

From grams of limiting reactant to theoretical yield to percent yield, in one chain — and backwards, to see what you should have recovered.

By Dr. Priya Nair, science writer and former university physics lecturer · Updated

Percent Yield Calculator

Enter any 5 known values — the others are solved as you type. Change units at any time.

Fill in the values you know.

How to use this calculator

Start from the balanced equation and identify the limiting reactant. Enter its mass and molar mass, the mole ratio of product to reactant from the coefficients (for 2 H₂ + O₂ → 2 H₂O with hydrogen limiting, the ratio is 2 / 2 = 1), and the product’s molar mass. The theoretical yield appears; add the mass you actually isolated to get the percent yield.

If you already know the theoretical yield, type it directly with the actual yield. Running backwards is handy for planning: enter a target mass of product and an expected percent yield, and the calculator tells you how much reactant to start with. Use the molar mass calculator to get molar masses from formulas.

The formula

n_R = m_R / M_R
n_P = ν × n_R
m_theo = n_P × M_P
%Y = m_act / m_theo × 100%
m_R
mass of limiting reactant
M_R
molar mass of limiting reactant
n_R
moles of limiting reactant
ν
mole ratio (mol product per mol reactant)
n_P
theoretical moles of product
M_P
molar mass of product
m_theo
theoretical yield
m_act
actual yield
%Y
percent yield

Worked example

Heating 10.0 g of calcium carbonate decomposes it: CaCO₃ → CaO + CO₂. You recover 5.00 g of calcium oxide. What is the percent yield?

  1. Moles of CaCO₃ = 10.0 / 100.09 = 0.09991 mol; the mole ratio CaO : CaCO₃ is 1 : 1.
  2. Theoretical yield = 0.09991 × 56.08 = 5.603 g CaO.
  3. Percent yield = 5.00 / 5.603 × 100 = 89.2%.

The reaction gave 89% of the maximum possible calcium oxide.

Assumptions and limits

  • The reactant entered is the limiting reactant; if not, the theoretical yield will be overstated.
  • Percent yields above 100% usually mean the product is wet or impure, not that the reaction made extra.

Frequently asked questions

What is a good percent yield?

It depends on the reaction. In teaching labs 70–90% is typical; multi-step syntheses multiply the losses, so a five-step route at 80% per step gives only 33% overall.

How do I find the limiting reactant?

Divide the moles of each reactant by its coefficient in the balanced equation. The smallest result identifies the limiting reactant.

Can percent yield be over 100%?

Not for a pure, dry product. Values above 100% point to residual solvent, moisture or side products in the weighed material.

Sources

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