Percent Yield Calculator — Actual vs. Theoretical Yield
Calculate percent yield for chemical reactions. Enter actual and theoretical yield to find efficiency, or work backward to find what you needed to produce a target amount.
No real chemical reaction runs at 100% efficiency. Side reactions happen, products are lost during purification, reagents aren't perfectly pure, and some reactions simply don't go to completion. Percent yield puts a number on how close you got to the theoretical maximum. The CalcHub Percent Yield Calculator handles the calculation both ways — giving yield percentage or working backward to find theoretical yield from an actual amount.
The Formula
% Yield = (Actual Yield / Theoretical Yield) × 100
- Actual yield: What you physically obtained and measured (in grams or moles)
- Theoretical yield: The maximum possible based on stoichiometry (assuming 100% conversion)
How to Use the Calculator
- Open CalcHub and select the Percent Yield Calculator.
- Enter your actual yield and the theoretical yield in the same units.
- The percent yield is returned immediately.
Worked Example
You're synthesizing aspirin (C₉H₈O₄, MW = 180.16 g/mol) from 5.0 g of salicylic acid (C₇H₆O₃, MW = 138.12 g/mol).
Theoretical yield:
- Moles of salicylic acid = 5.0 / 138.12 = 0.0362 mol
- Mole ratio is 1:1, so 0.0362 mol aspirin expected
- Theoretical mass = 0.0362 × 180.16 = 6.52 g
You actually collected 5.1 g after drying.
% Yield = (5.1 / 6.52) × 100 = 78.2%
What's a Good Percent Yield?
| Range | Interpretation |
|---|---|
| > 90% | Excellent — industrial-grade |
| 70 – 90% | Good — typical in well-optimized lab syntheses |
| 50 – 70% | Acceptable — common in teaching labs |
| < 50% | Low — indicates side reactions, poor purification, or procedural issues |
| > 100% | Error — product contaminated, insufficiently dried, or calculation mistake |
Common Reasons for Low Yield
- Incomplete reaction: Equilibrium disfavors product at the conditions used
- Side reactions: Reagents form byproducts instead of desired product
- Purification losses: Filtering, washing, recrystallizing all lose some product
- Transfer losses: Sticking to glassware, pipette walls, filter paper
- Impure reagents: If your starting material isn't pure, fewer moles react than you calculate
Can percent yield ever exceed 100%?
Not in a real, valid experiment. If you calculate a yield above 100%, the product is likely contaminated (contains solvent, unreacted starting material, or byproducts), was not fully dried before weighing, or there's an error in the theoretical yield calculation.
How is percent yield different from atom economy?
Percent yield measures how much of the theoretical maximum you actually collected. Atom economy measures what fraction of all reactant atoms end up in the desired product (ignoring byproducts). A reaction can have 100% percent yield but poor atom economy if it generates a lot of waste byproducts.
Should I report percent yield in a lab report?
Yes — it's standard practice in synthesis lab reports. It tells readers how efficient the procedure was and helps them troubleshoot if they try to replicate it. Report theoretical yield, actual yield, and percent yield clearly with units.
Related calculators: Stoichiometry Calculator · Limiting Reagent Calculator · Molar Mass Calculator