Percent Yield Calculator
Calculate percent yield of a chemical reaction: (actual yield ÷ theoretical yield) × 100. Enter masses in any consistent unit (g, mg, kg). For education only.
How to use this tool
- Enter actual yield and theoretical yield in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your percent yield and the full breakdown beneath it.
Percent yield measures reaction efficiency: % yield = (actual ÷ theoretical) × 100. A yield of 100% means all theoretical product was collected; in practice losses from side reactions, incomplete reactions and handling reduce the yield.
For education only.
Formula
% yield = (actual yield ÷ theoretical yield) × 100
Mass not obtained: wasted = theoretical yield − actual yield
How it works
This calculator divides the actual (experimentally measured) yield by the theoretical (maximum possible) yield and multiplies by 100 to give the percent yield — the standard metric for evaluating reaction efficiency in chemistry.
Both yields must be in the same mass unit (g, mg, kg, etc.). The calculator enforces that actual yield cannot exceed theoretical yield by more than 0.1 %, guarding against data-entry errors. Losses to side reactions, incomplete conversion, and purification steps are normal reasons for yields below 100 %.
Worked example
Worked example: yield of a synthesis reaction
- Identify inputs: actual yield = 4.5 g, theoretical yield = 6.0 g.
- Apply the formula: % yield = (4.5 ÷ 6.0) × 100 = 75.0 %.
- Calculate mass not obtained: wasted = 6.0 − 4.5 = 1.5 g.
Percent yield = 75.0 %; Mass not obtained = 1.5 g
Common mistakes to avoid
- Entering actual yield larger than theoretical yield -- this gives over 100%, which is physically impossible and usually indicates impurities or moisture in the product.
- Using inconsistent mass units -- if actual yield is in grams and theoretical yield is in milligrams, the result is off by 1000x; use the same unit for both.
- Confusing percent yield with atom economy -- percent yield measures how much of the theoretical product you obtained; atom economy measures how much reactant mass ends up in the product.
Key terms
- Theoretical yield
- The maximum mass of product that could form if the reaction went to completion with no losses; calculated from stoichiometry.
- Actual yield
- The mass of product actually isolated and measured after the reaction and purification.
- Percent yield
- The ratio of actual to theoretical yield expressed as a percentage; 100 % would mean a perfect, lossless reaction.
- Limiting reagent
- The reactant that is completely consumed first and thus determines the theoretical yield.
- Side reaction
- An unintended reaction that consumes reactants or products, reducing the actual yield.
Frequently asked questions
- Can percent yield exceed 100%?
- No — a yield above 100% indicates an error such as impure product, incomplete drying, or a mistake in calculating the theoretical yield.
- What is a 'good' percent yield?
- Depends on the reaction. Industrial processes often target >90%; complex organic syntheses may only achieve 30–50% per step.