The limiting reagent calculator identifies which reactant runs out first in a chemical reaction, calculates the theoretical yield of the product, and determines percent yield if the actual yield is known. Enter reactant masses and the balanced equation stoichiometry.
Limiting Reagent Calculator
Select a preset reaction or enter custom stoichiometry manually.
Reactant A
Reactant B
Product
Results
Step-by-Step
How to Use the Limiting Reagent Calculator
Identifying the limiting reagent requires comparing the available moles of each reactant to the stoichiometric ratio in the balanced equation. The reactant that provides fewer moles per stoichiometric unit is the limiting reagent.
Step 1: Select or Enter the Reaction
Choose a preset reaction from the dropdown or enter custom values. For custom reactions, enter the chemical formula, molar mass, stoichiometric coefficient, and available mass for each reactant, plus the product information.
Step 2: Enter Available Masses
Enter the mass (in grams) of each reactant you have available. The calculator converts to moles using the molar mass you provided.
Example: Water Synthesis
2H₂ + O₂ → 2H₂O. If you have 10g H₂ (MW=2.016) and 20g O₂ (MW=32). Moles H₂ = 10/2.016 = 4.96 mol. Moles O₂ = 20/32 = 0.625 mol. Ratio check: H₂ needs 2×O₂, so compare 4.96/2 = 2.48 vs 0.625/1 = 0.625. O₂ is smaller → O₂ is the limiting reagent.
Percent Yield
Optionally enter the actual yield obtained from your experiment. Percent yield = (actual/theoretical) × 100%. A 75% yield from the above example would give: 75% × theoretical yield grams of water.
FAQ
What is the limiting reagent?
The limiting reagent (or limiting reactant) is the reactant that is completely consumed first in a chemical reaction, limiting the amount of product that can be formed. The other reactants are in excess. Identifying it is essential for calculating theoretical yield.
How do I find the limiting reagent step by step?
Step 1: Convert grams of each reactant to moles using molar mass. Step 2: Divide moles by the stoichiometric coefficient in the balanced equation. Step 3: The reactant with the smallest result is the limiting reagent.
What is theoretical yield?
Theoretical yield is the maximum amount of product that could be formed if all the limiting reagent reacted completely, with no losses. Real reactions give less — the percent yield = (actual yield / theoretical yield) × 100%.
Is this calculator free?
Yes, completely free with no signup required. All calculations run in your browser.
What is a good percent yield?
In industrial chemistry, yields above 90% are excellent. In organic synthesis, 70-80% is often considered good. Many complex multi-step syntheses achieve only 20-40%. Losses come from side reactions, incomplete reactions, and physical handling.