Percent Yield Calculator:
actual vs theoretical yield.

Guide

Synthesis efficiency, from the formula to the bench.

Percent yield is the cleanest way to compare what a reaction did produce to what it could haveproduced. It’s the central efficiency metric in preparative chemistry, used everywhere from undergraduate teaching labs to industrial process development.

The three formulas

Actual and theoretical yields must share a unit — grams with grams, moles with moles. The calculator above enforces this with a single unit dropdown that both sides use.

How theoretical yield is found

Theoretical yield comes from a properly balanced equation and the limiting reactant: the reactant that runs out first and therefore caps the amount of product. You convert the limiting reactant’s mass to moles, apply the stoichiometric ratio from the balanced equation, then convert back to mass using the product’s molar mass. If you’re unsure which reagent is limiting, our stoichiometry calculator and molecular weight calculator will get you there.

Why reactions don’t hit 100%

• Side reactions divert reagent into unwanted products.
• Equilibrium-limited systems never fully convert starting material.
• Transfer losses — every pour, filter, and wash leaves product behind.
• Purification trade-offs — recrystallisation, distillation, and chromatography all sacrifice mass for purity.
• Wet or impure product can falsely inflate the apparent yield above 100%.

Percent yield vs percent error

For routine syntheses, percent error simplifies to 100% − %Yield — a 70% yield is a 30% error. The two metrics diverge once a measured value exceeds the expected value, which is impossible for a real chemical yield but routine in other experimental measurements. Our percent error calculator is the right tool when you can over- or under-shoot the reference value in either direction.

Classifying your result

The scale used here — Poor (<40%), Moderate (40–70%), Good (70–90%), Excellent (≥90%) — is a rough teaching/practitioner heuristic, not a regulatory standard. Single-step, fast, clean reactions can routinely hit excellent yields; multi-step routes compound losses and are judged accordingly.

Disclaimer: Definitions follow the IUPAC 2021 Gold Book entry for “yield (in chemical reactions)” and unit handling follows the NIST Guide for the Use of the International System of Units (SP 811). The classification bands above are practical heuristics for teaching and bench work, not regulatory limits. For coursework, research papers, or process work, follow the specific conventions of your instructor, journal, or quality system.