The Percent Yield Formula (Chemistry)

The formula

percent yield = (actual yield ÷ theoretical yield) × 100

Where:

• Actual yield = the mass of product you measure after the reaction
• Theoretical yield = the mass you’d get if every reactant atom went into product (calculated from stoichiometry)

Why it’s rarely 100%

• Side reactions consume some reactant
• Product loss during isolation (filtering, transferring, drying)
• Reactions don’t go to completion at finite rates
• Impurity in starting material

A “good” percent yield is context-dependent. For straightforward reactions, 80–95% is achievable. For complex multistep syntheses, 30–50% per step is common.

Example

You start a reaction expecting 12.0 g of product (theoretical yield based on the limiting reagent). After the reaction and workup, you weigh 9.6 g of pure product.

9.6 ÷ 12.0 × 100 = 80%

That’s a respectable yield for many organic transformations.

Multistep yield

For a multi-step synthesis, the overall yield is the product of each step’s yield (as decimals), not the sum. Three steps at 80% each give:

0.80 × 0.80 × 0.80 = 0.512 = 51.2%

This is why total synthesis chemists obsess over high yields per step.