# What is my percent yield?

Finds the percent yield of a reaction from the actual and theoretical yield, or works out the theoretical yield from the limiting reactant first.

- Page: https://www.acalculator.org/chemistry/percent-yield-calculator
- JSON spec: https://www.acalculator.org/chemistry/percent-yield-calculator.json
- Version: b7fa85027d03

## Default answer

Example with the default inputs (Theoretical yield I know it, Actual yield 0.392 g, Theoretical yield 0.5072 g): Your percent yield is 77.29%: 0.392 g of 0.5072 g.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| mode | Theoretical yield | Type the theoretical yield, or let the page find it from the limiting reactant. |
| a | Actual yield | The mass of product you obtained. |
| t | Theoretical yield | The mass of product the balanced equation predicts. |
| r | Mass of limiting reactant | The mass of the reactant that runs out first. |
| mr | Reactant molar mass | The molar mass of the limiting reactant, in g/mol. |
| cr | Reactant coefficient | The limiting reactant’s coefficient in the balanced equation. |
| cp | Product coefficient | The product’s coefficient in the balanced equation. |
| mp | Product molar mass | The molar mass of the product, in g/mol. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| percent | Percent yield | Actual yield ÷ theoretical yield × 100. |
| theoreticalGrams | Theoretical yield (g) | The theoretical yield in grams. |
| actualGrams | Actual yield (g) | The actual yield in grams. |
| productMoles | Theoretical product (mol) | Moles of limiting reactant × product coefficient ÷ reactant coefficient. |
| note | Note | Shown when the percent yield is over 100%. |

## Method

Percent yield = actual yield ÷ theoretical yield × 100. From the limiting reactant: theoretical yield = reactant mass ÷ reactant molar mass × (product coefficient ÷ reactant coefficient) × product molar mass.

## Assumptions

- The reactant you type is the limiting reactant: the one that runs out first. Check it with the mole ratios before you use this mode.
- Molar masses are typed in g/mol; masses can be typed in g, mg, kg, oz or lb and are worked in grams.
- Each typed mass and molar mass is used as the exact decimal you typed; the result is rounded once.

## Worked examples

1. mode = yields, a = 0.000392, t = 0.000507 gives percent = 77.287066%, theoreticalGrams = 0.5072, actualGrams = 0.392. Source: OpenStax, Chemistry 2e, §4.4 Reaction Yields, https://openstax.org/books/chemistry-2e/pages/4-4-reaction-yields (Example 4.13: 0.392 g ÷ 0.5072 g × 100% = 77.3%).
2. mode = reactant, a = 0.000392, r = 0.001274, mr = 159.62, cr = 1, cp = 1, mp = 63.55 gives percent = 77.283786%, theoreticalGrams = 0.507222, productMoles = 0.007981. Source: OpenStax, Chemistry 2e, §4.4 Reaction Yields, https://openstax.org/books/chemistry-2e/pages/4-4-reaction-yields (Example 4.13: 1.274 g CuSO₄ ÷ 159.62 g/mol × 63.55 g/mol = 0.5072 g Cu).
3. mode = reactant, a = 0.0125, r = 0.0329, mr = 153.81, cr = 1, cp = 1, mp = 120.91 gives percent = 48.332189%, theoreticalGrams = 25.862681. Source: OpenStax, Chemistry 2e, §4.4 Reaction Yields, https://openstax.org/books/chemistry-2e/pages/4-4-reaction-yields (Check Your Learning after Example 4.13: 48.3%).
4. mode = reactant, a = 0.01, r = 0.004, mr = 2, cr = 2, cp = 2, mp = 18 gives percent = 27.777778%, theoreticalGrams = 36, productMoles = 2. Source: OpenStax, Chemistry 2e, §4.4 Reaction Yields, https://openstax.org/books/chemistry-2e/pages/4-4-reaction-yields.

## FAQ

### What is the percent yield formula?

Percent yield = actual yield ÷ theoretical yield × 100%. If a reaction should give 0.5072 g of copper and you collect 0.392 g, the percent yield is 0.392 ÷ 0.5072 × 100 = 77.3%.

### How do I find the theoretical yield?

Convert the mass of the limiting reactant to moles (divide by its molar mass), multiply by the mole ratio from the balanced equation (product coefficient ÷ reactant coefficient), and convert to grams (multiply by the product’s molar mass).

### Can percent yield be over 100%?

Not for a pure, dry product. A result over 100% usually means the product still holds water or solvent, has an impurity, or a mass was weighed or typed wrong. The page still shows the number and adds a note.

### Why is percent yield usually below 100%?

Side reactions make other products, reactions may not go to completion, and some product is lost when it is filtered, moved or purified.

### What is the limiting reactant?

The reactant that runs out first. It sets how much product can form. To find it, convert each reactant to moles and divide by its coefficient; the smallest result is the limiting reactant.

### Which units can I use?

Masses in grams, milligrams, kilograms, ounces or pounds; molar masses in g/mol. Both yields must be the same substance, so the ratio has no unit.

## Sources

- OpenStax, Chemistry 2e, §4.4 Reaction Yields (percent yield = actual ÷ theoretical × 100%; Example 4.13 and its Check Your Learning). https://openstax.org/books/chemistry-2e/pages/4-4-reaction-yields (retrieved 2026-10-02)
- NIST Special Publication 811, Guide for the Use of the International System of Units, Appendix B (1 oz = 28.349523125 g, 1 lb = 453.59237 g). https://www.nist.gov/pml/special-publication-811 (retrieved 2026-10-02)