Theoretical Yield CalculatorThe most product your reaction can make, and the reactants you need for a target
Balance any equation, enter reactants as solids, solutions or gases, and plan a batch with your real-world percent yield built in.
By Manzoor Ahmad, web development expert · Updated How do you calculate theoretical yield?
Theoretical yield = moles of limiting reactant × (product coefficient ÷ reactant coefficient) × molar mass of product. For aspirin, 2.00 g of salicylic acid (138.122 g/mol) is 0.01448 mol; with a 1 : 1 ratio and aspirin’s molar mass of 180.159 g/mol, the theoretical yield is 0.01448 × 180.159 = 2.609 g.
Theoretical yield formula
Four ways a reactant can be measured
How to use the theoretical yield calculator
- Enter the reaction and press Balance & load. Coefficients are added if missing.
- Pick the product you care about.
- Theoretical yield mode: for each reactant, choose mass, moles, solution or gas and enter the amount. The limiting reactant is found automatically.
- Plan mode: enter how much product you want, your expected yield and any excess, and get the grams of every reactant to weigh.
Worked examples
1. Aspirin synthesis
2.00 g salicylic acid (0.01448 mol) and 5.4 g acetic anhydride (0.0529 mol) react 1 : 1. Salicylic acid is limiting, so aspirin = 0.01448 × 180.159 = 2.609 g. At a typical 85% yield you would expect to collect about 2.22 g.
2. Neutralisation with a solution
25.0 mL of 0.100 M HCl with excess NaOH: n(HCl) = 0.100 × 0.0250 = 0.00250 mol, giving 0.00250 mol NaCl = 0.146 g.
3. Planning 10 g of ammonia
At 85% yield you need a theoretical 11.76 g NH₃ (0.6908 mol). That requires 0.3454 mol N₂ = 9.68 g, and with 10% excess H₂, 1.036 mol × 1.10 × 2.016 = 2.30 g H₂.
Theoretical yield FAQs
Theoretical yield is the maximum amount of product a reaction can form from the given reactants, assuming the limiting reactant is completely converted and nothing is lost.
Balance the equation, convert reactants to moles, find the limiting reactant, multiply its moles by the product-to-reactant mole ratio, then multiply by the product's molar mass.
Theoretical yield (g) = moles of limiting reactant × (product coefficient ÷ limiting reactant coefficient) × molar mass of product.
Moles = molarity × volume in liters. 25.0 mL of 0.100 M HCl contains 0.100 × 0.0250 = 0.00250 mol. Choose the solution input in the calculator and enter both values.
At STP (0 °C, 1 atm) one mole of an ideal gas occupies 22.414 L; at 25 °C and 1 bar it occupies 24.79 L. Divide the volume by the molar volume to get moles. For other conditions use the ideal gas law calculator.
Theoretical yield is calculated from the equation. Actual yield is the mass you collect in the lab, which is normally lower because of losses and side reactions.
Divide the target mass by the expected fractional yield, convert to moles of product, use the mole ratio to get moles of each reactant, then convert to grams. The scale-up planner does this for every reactant.
Using a cheaper reactant in excess ensures the more valuable one is completely consumed and pushes the reaction toward completion. The planner lets you add a percentage of excess to non-limiting reactants.
Yes. The calculator reports theoretical yield in both moles and grams. Moles are useful when the product is used directly in a further reaction.
No. Theoretical yield is fixed by stoichiometry. Percent yield only describes how much of that theoretical maximum you actually obtained.
This calculator always finds the limiting reactant automatically, so the theoretical yield is based on the reactant that truly runs out first.
Not in reality. A measured yield above the theoretical value means the product is wet or impure, or a calculation error was made.
Sources
This theoretical yield calculator assumes complete reaction as written and ideal-gas behaviour for gas inputs. Real yields are lower; follow your validated procedures for scale-up.