What this calculator does
A theoretical yield calculator works out the maximum possible mass of product a reaction could give, based purely on how much limiting reagent goes in and the balanced equation ratio between it and the product. This is the number every real result gets compared against: no reaction is 100% efficient, so the actual yield obtained is always the theoretical yield or less.
The calculation runs in two stages. First the mass of the limiting reagent is converted to moles using its molar mass, since a balanced equation works in moles, not grams. Then that mole amount is scaled by the stoichiometric ratio between the reagent and the desired product, and converted back to a mass using the product's molar mass. Enter an actual yield as well and the calculator also reports the percent yield, how to calculate theoretical yield being the first half of that comparison.
The formula
Moles of limiting reagent = mass ÷ molar mass. Moles of product = moles of reagent × (product coefficient ÷ reagent coefficient), using the numbers in front of each substance in the balanced equation. Theoretical yield = moles of product × molar mass of product.
| Term | Meaning |
|---|---|
| Limiting reagent | The reactant that runs out first, and so sets the maximum amount of product possible. |
| Molar mass | The mass of one mole of a substance, in grams per mole, found by summing the atomic masses of its atoms. |
| Stoichiometric coefficient | The number in front of a substance in a balanced equation, showing how many moles of it react or form relative to the others. |
| Percent yield | Actual yield divided by theoretical yield, as a percentage. Always 100% or less for a real reaction. |
The inputs explained
| Field | What to enter |
|---|---|
| Mass of limiting reagent (g) | The mass of the limiting reagent actually used or available. |
| Molar mass of limiting reagent (g/mol) | The molar mass of the limiting reagent, in grams per mole. |
| Stoichiometric coefficient of the limiting reagent | The coefficient of the limiting reagent in the balanced equation. Leave at 1 if the equation is not scaled. |
| Stoichiometric coefficient of the desired product | The coefficient of the desired product in the same balanced equation. |
| Molar mass of the desired product (g/mol) | The molar mass of the desired product, in grams per mole. |
| Actual yield obtained, if known (0 to skip) (g) | Optional: the mass of product actually obtained, if known, to also see the percent yield. Leave at 0 to skip. |
When to use it
Planning how much product a reaction should give
Before running a synthesis, working out the theoretical yield from the reagent on hand sets an expectation for how much product should be recoverable, and whether the batch size is worth the reagent used.
Checking a lab result against the maximum possible
After weighing the actual product obtained, comparing it with the theoretical yield gives the percent yield, a standard way to judge how efficiently a reaction or purification went.
Working from a molar-mass-only reagent quantity
When a reagent amount is already given as a mass with a known molar mass, this calculator skips straight to the mole-ratio step rather than needing a separate mole conversion first.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Theoretical yield of silver chloride from varying reagent mass
Sodium chloride (molar mass 58.44 g/mol) reacting with excess silver nitrate to form silver chloride (molar mass 143.32 g/mol), across a range of starting reagent masses.
| Mass of NaCl | Theoretical yield | Moles of limiting reagent |
|---|---|---|
| 5 g | 12.262 g | 0.0856 mol |
| 10 g | 24.524 g | 0.1711 mol |
| 20 g | 49.049 g | 0.3422 mol |
| 50 g | 122.621 g | 0.8556 mol |
| 100 g | 245.243 g | 1.711 mol |
Percent yield for different actual results, same reaction
The same theoretical yield compared against a range of actual yields that might be weighed out after the reaction and any purification.
| Actual yield obtained | Theoretical yield | Percent yield (actual ÷ theoretical × 100) |
|---|---|---|
| 15 g | 24.524 g | 61.2% |
| 18 g | 24.524 g | 73.4% |
| 20 g | 24.524 g | 81.6% |
| 22 g | 24.524 g | 89.7% |
| 24.524 g | 24.524 g | 100.0% |
Questions
What is the theoretical yield formula?
Theoretical yield = (mass of limiting reagent ÷ its molar mass) × (product coefficient ÷ reagent coefficient) × molar mass of product. It converts the reagent to moles, applies the balanced equation ratio, then converts the resulting moles of product back to a mass.
How do I calculate theoretical yield without a balanced equation?
You need the balanced equation, or at least the mole ratio between the limiting reagent and the product, since that ratio is what links moles of one substance to moles of the other. For a 1:1 reaction, set both coefficients to 1.
What is the difference between theoretical and actual yield?
Theoretical yield is the maximum mass of product possible if the reaction went to completion with no losses. Actual yield is what is actually weighed out afterwards, which is always equal to or less than the theoretical yield because of side reactions, incomplete conversion or losses during purification.
How is percent yield related to theoretical yield?
Percent yield = actual yield ÷ theoretical yield × 100. It needs the theoretical yield as its denominator, which is exactly what this calculator works out first before comparing it with an actual result.
For the mole ratio between two substances in a balanced equation on its own, see the mole ratio calculator. To convert a single mass to moles or back, see the mole calculator.