Theoretical Yield Calculator

The Theoretical Yield Calculator finds the maximum amount of product a reaction can make from the reactants you have. Enter any balanced chemical equation, choose the product you care about, and enter how much of each reactant you have in grams or moles. The calculator reports the theoretical yield in both grams and moles, identifies the limiting reactant, and shows the excess reactant left over. Molar masses are parsed automatically, and a visual "yield race" shows how much product each reactant could make on its own — the smallest amount is the theoretical yield. You can also enter an actual yield to get the percent yield.

What Is Theoretical Yield?

Theoretical yield is the maximum amount of product a reaction can produce, assuming the reaction goes perfectly to completion with no losses. It is determined by the limiting reactant — the reactant that runs out first. Once the limiting reactant is gone, the reaction stops, so it sets a hard ceiling on how much product can form, no matter how much of the other reactants remain. Theoretical yield is the benchmark against which real (actual) lab results are compared.

How to Calculate Theoretical Yield

The most reliable approach is the mole ratio (product potential) method:

1. Balance the equation so the coefficients give the correct mole ratios.
2. Convert each reactant to moles by dividing its mass by its molar mass (skip this if you already have moles).
3. Use the mole ratio to find how many moles of product each reactant could make: multiply the reactant's moles by (product coefficient ÷ reactant coefficient).
4. The smallest result is the theoretical yield in moles. The reactant that produced it is the limiting reactant.
5. Multiply by the product's molar mass to convert the theoretical yield to grams.

Theoretical Yield vs. Actual Yield vs. Percent Yield

The theoretical yield is the best-case maximum from stoichiometry. The actual yield is what you measure in the lab, which is almost always lower because of side reactions, losses during transfer and purification, and reactions that do not go fully to completion. The percent yield tells you how efficient the reaction was:

Worked Example

Consider the Haber process making ammonia: N₂ + 3 H₂ → 2 NH₃, starting with 28 g of N₂ and 10 g of H₂. We want the theoretical yield of NH₃ (molar mass 17.03 g/mol).

N₂ could make only 2.00 mol of NH₃, less than the 3.31 mol H₂ could make, so N₂ is the limiting reactant. The theoretical yield is 2.00 mol of NH₃, which is 2.00 × 17.03 ≈ 34.1 g of NH₃. The leftover H₂ is the excess reactant.

Common Mistakes

• Forgetting to balance the equation. The coefficients are the mole ratios — without them the answer is wrong.
• Comparing grams instead of moles. Always convert to moles first; equal masses are not equal numbers of particles.
• Using the wrong mole ratio. Multiply by (product coefficient ÷ reactant coefficient), not the other way around.
• Assuming the reactant with the smallest mass is limiting. Molar mass and coefficients decide it, not raw mass.
• Confusing theoretical and actual yield. Theoretical is the calculated maximum; actual is what you measure.

How to Use This Calculator

1. Enter a balanced equation such as N2 + 3 H2 -> 2 NH3. Use -> or = for the arrow and + between species. Input boxes appear automatically.
2. Choose the product you want the theoretical yield for.
3. Enter each reactant's amount and pick grams or moles.
4. (Optional) Enter an actual yield to also get the percent yield.
5. Click Calculate to see the theoretical yield, the yield race, the limiting reactant, the excess left over, and a full step-by-step solution.

Frequently Asked Questions

What is theoretical yield?

Theoretical yield is the maximum amount of product that a reaction can make from the given reactants, assuming the reaction goes to completion with no losses. It is set by the limiting reactant and is calculated from the mole ratios in the balanced equation.

How do you calculate theoretical yield?

Convert each reactant to moles, use the mole ratio in the balanced equation to find how much product each reactant could make, and take the smallest result. That smallest value is the theoretical yield in moles. Multiply it by the product's molar mass to get grams.

How is theoretical yield related to the limiting reactant?

The limiting reactant is the one that can make the least product, so it sets the theoretical yield. Once it runs out the reaction stops, no matter how much of the other reactants remain.

What is the difference between theoretical yield and actual yield?

Theoretical yield is the maximum predicted by stoichiometry. Actual yield is what you actually obtain in the lab, which is usually lower because of side reactions, losses during transfer, and incomplete reactions.

Does the equation need to be balanced?

Yes. The coefficients in a balanced equation give the mole ratios used to calculate the theoretical yield. If the equation is not balanced, balance it first or the result will be wrong.

How do you calculate percent yield from theoretical yield?

Percent yield equals the actual yield divided by the theoretical yield, multiplied by 100. For example, an actual yield of 12 g against a theoretical yield of 15 g is 80 percent.

Additional Resources

• Yield (Chemistry) - Wikipedia
• Limiting Reagent - Wikipedia