📊 Percent Yield

Written and maintained by the PhDino author · Last reviewed 21 September 2026 · Checked against 1 independent reference calculation · how PhDino checks its numbers

How a reaction's actual, measured output compares to the maximum stoichiometry predicts.

Stoichiometry predicts a theoretical yield — the maximum amount of product possible if the limiting reagent reacted completely and nothing was lost along the way. Real reactions almost always produce less than that, for reasons ranging from an equilibrium that doesn't fully favor products, to side reactions consuming some of the starting material, to simple mechanical loss during transfer, filtration, or purification.

Percent yield is simply how the actual, measured product mass compares to that theoretical maximum, expressed as a percentage. It's one of the most basic checks in experimental chemistry — a yield far below expectation is often the first sign something in a procedure needs troubleshooting.

Key formula

Percent yield = (actual yield ÷ theoretical yield) × 100%

Notes & limitations

• A percent yield over 100% is possible in practice, but it's a red flag rather than good news — it usually means the product wasn't fully dried (residual solvent adding weight) or was contaminated with something else, not that more product formed than the reaction stoichiometry allows.
• Theoretical yield itself comes from a stoichiometry calculation using the limiting reagent — percent yield only makes sense once that number is already known.