Percent Yield Calculator — Actual vs Theoretical Yield

Calculate percent yield from actual and theoretical yield in grams or moles. Instant result plus a plain-language read on what your yield suggests.

July 13, 2026

Actual Yield

Theoretical Yield

Unit

Unit is just a label here — the math is identical for grams or moles as long as both yields use the same unit.

Percent Yield

83.41%

3.42 g actual ÷ 4.10 g theoretical × 100

Good yield — the most common range for routine lab work. Some product is lost to transfer steps, incomplete reaction, or purification.

Percent Yield = (Actual Yield ÷ Theoretical Yield) × 100. Actual yield is the amount you actually measured in the lab; theoretical yield is the maximum possible amount from stoichiometry, assuming 100% conversion with no losses. This calculator checks a reported theoretical yield — it doesn't derive one from a balanced chemical equation.

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Reference Values

Last verified: Jul 11, 2026

Category	Range	What It Means	Status
90–100% ★	Excellent yield	Close to the theoretical maximum. Typical of clean, efficient reactions with minimal side reactions, careful technique, and thorough (but not excessive) purification.	★ Best
70–90%	Good yield	The most common range reported in undergraduate and routine synthetic lab work. Some product is lost to transfer steps, incomplete reactions, or purification (recrystallization, filtration).	Good
50–70%	Acceptable yield	Workable but shows meaningful losses — often from side reactions competing with the main pathway, an equilibrium-limited reaction, or a multi-step purification.	Okay
Below 50%	Low yield	Signals a real problem: incomplete reaction, a dominant side reaction, a limiting-reagent miscalculation, or significant product lost during transfer/purification/filtration.	Poor
Above 100%	Over-theoretical yield	Not "better than perfect." Almost always means the measured product still contains impurities, residual solvent, or moisture that add extra mass — or a measurement/calculation error. Re-dry and re-weigh before trusting a result over 100%.	Poor

Source: Percent yield formula and typical undergraduate-lab yield ranges per LibreTexts Chemistry, "Theoretical Yield and Percent Yield" (chem.libretexts.org). Range bands reflect common general-chemistry lab conventions — individual reactions and instructors vary.

Worked Examples

Typical Good Lab Yield

Actual Yield: 3.42 g
Theoretical Yield: 4.10 g

83.4% yield

(3.42 ÷ 4.10) × 100 = 83.4% — a solid, realistic result for a routine synthesis with some transfer and purification loss.

Excellent, Near-Complete Reaction

Actual Yield: 9.61 g
Theoretical Yield: 10.00 g

96.1% yield

(9.61 ÷ 10.00) × 100 = 96.1% — close to the theoretical maximum, typical of a clean, high-efficiency reaction.

Low Yield From a Side Reaction

Actual Yield: 1.85 g
Theoretical Yield: 5.20 g

35.6% yield

(1.85 ÷ 5.20) × 100 = 35.6% — well below 50% suggests a competing side reaction, an incomplete reaction, or major product loss during purification.

Yield in Moles Instead of Mass

Actual Yield: 0.0842 mol
Theoretical Yield: 0.100 mol

84.2% yield

(0.0842 ÷ 0.100) × 100 = 84.2%. The formula works identically whether both yields are in grams or in moles — it just needs matching units.

Over 100% — Likely Impure or Wet Product

Actual Yield: 5.35 g
Theoretical Yield: 5.00 g

107.0% yield

(5.35 ÷ 5.00) × 100 = 107.0%. A result over 100% is not a better-than-perfect reaction — it almost always means the isolated product still contains residual solvent, moisture, or an unreacted impurity adding extra mass. Drying the sample fully and re-weighing usually brings this back under 100%.

How to Use This Calculator

1

Find or calculate your theoretical yield

This is the maximum product possible from your reaction's stoichiometry, assuming 100% conversion of the limiting reagent with no losses — usually given in your lab manual or calculated separately.
2

Weigh or measure your actual yield

The amount of product you actually isolated and measured after the reaction and any purification steps, in the same unit as your theoretical yield.
3

Enter both values

Type the actual yield and theoretical yield into the calculator. The unit selector (grams or moles) is just a label — the math is identical either way.
4

Read your percent yield and its interpretation

The result updates instantly and includes a plain-language note on what your yield range typically suggests, including a flag if it's over 100%.

What Each Value Means

Actual Yield (g or mol): The amount of product you actually obtained and measured in the lab after the reaction and any purification steps — always a real, weighed or measured quantity.
Theoretical Yield (g or mol): The maximum possible amount of product predicted by reaction stoichiometry, assuming the limiting reagent converts completely with no losses or side reactions.
Percent Yield (%): The ratio of actual yield to theoretical yield, expressed as a percentage — a measure of how efficiently a reaction was carried out in practice compared to the ideal case.

Frequently Asked Questions

What is the percent yield formula?

Percent Yield = (Actual Yield ÷ Theoretical Yield) × 100. Actual yield is the amount of product you actually measured after the reaction and any purification. Theoretical yield is the maximum possible amount predicted by stoichiometry, assuming the limiting reagent converts completely with zero losses. Both values must be in the same unit — grams and grams, or moles and moles.

Why is percent yield usually less than 100%?

Real reactions almost never hit their theoretical maximum. Product is lost during transfer between containers, some reactant is diverted into side reactions, the reaction may not go to completion (especially if it's reversible or equilibrium-limited), and purification steps like recrystallization or filtration intentionally sacrifice some product to remove impurities. A yield in the 70-90% range is considered good for typical lab work.

Can percent yield be over 100%? What does that mean?

Yes, and it happens more often than beginners expect — but it is not a sign of an unusually efficient reaction. A result above 100% almost always means the isolated "product" still contains extra mass that shouldn't be there: residual solvent, absorbed moisture, an unreacted starting material, or another impurity that was weighed along with the real product. It can also come from a measurement or calculation error. The fix is usually to dry the sample fully (e.g., in a desiccator or oven) and re-weigh — a properly dried product should come back under 100%.

Do I need a balanced chemical equation to use this calculator?

No. This calculator checks a percent yield once you already know (or have been given) both the actual yield and the theoretical yield — it doesn't derive theoretical yield from a balanced equation and starting reagent amounts, which requires a full stoichiometry calculation (molar masses, mole ratios, and identifying the limiting reagent). If your assignment gives you a theoretical yield or asks you to calculate one from an equation, do that step first, then enter the result here.

Does it matter if I use grams or moles for actual and theoretical yield?

No — the percent yield formula is a ratio, so the units cancel out as long as both the actual and theoretical yield are expressed in the same unit. 3.42 g actual over 4.10 g theoretical gives the same 83.4% as 0.00834 mol over 0.0100 mol theoretical, assuming those numbers represent the same reaction. Just don't mix grams in one field with moles in the other.