Understanding percent yield
No chemical reaction is perfectly efficient. Side reactions, incomplete conversion, mechanical losses during transfer and purification, and equilibrium limitations all reduce how much product you actually collect compared to what’s theoretically possible.
Percent yield quantifies this efficiency. A 100% yield means every molecule of starting material converted to product and you recovered all of it — essentially impossible in practice. Real yields are always somewhat lower, and understanding why helps chemists optimise reactions.
The most common mistake is using the wrong theoretical yield — often by forgetting to account for a limiting reagent, or by confusing mass with moles during the calculation.
How to Calculate Percent Yield (step by step)
Step One: Determine your theoretical yield
Calculate the maximum possible product from your limiting reagent using stoichiometry. This is what you’d get with 100% efficiency.
theoretical yield = from stoichiometric calculation
For this example: 10 g theoretical yield.
Step Two: Measure your actual yield
Weigh the purified product you actually isolated from the reaction.
actual yield = mass of isolated product
For this example: 8.5 g actual yield.
Step Three: Divide and multiply by 100
percent yield = (actual yield ÷ theoretical yield) × 100
For this example: (8.5 ÷ 10) × 100 = 85.00%.