Theoretical Yield Calculator
Enter the mass and molar mass of your limiting reactant, plus the stoichiometric coefficients from the balanced equation, to calculate moles of product and the theoretical yield in grams.
Reviewed by the ToolNestr Editorial Team — July 2026
Limiting reactant
Product
Two ideas that trip students up
1. The mole ratio can shrink or match the pile
The left pile (reactant, in moles) converts into the right pile (product, in moles) using the mole ratio from the balanced equation — here NH₃:H₂ = 2:3, so the product pile ends up smaller.
2. Theoretical yield scales linearly with mass
Three reactant masses, same mole ratio and molar masses — doubling the starting mass simply doubles the theoretical yield.
Theoretical yield graphs
How it works
The core idea in one line: theoretical yield is the mass of product a reaction could form if the limiting reactant converted completely — found by walking mass → moles → moles of product (via the mole ratio) → mass of product.
mol reactant = mass ÷ Mreactant
mass to moles
mol product = mol reactant × (coeffproduct ÷ coeffreactant)
mole ratio from balanced equation
theoretical yield = mol product × Mproduct
moles to mass of product
This calculator does the full stoichiometric chain for you: it converts the limiting reactant's mass to moles, applies the mole ratio (coefficient of product ÷ coefficient of reactant) from your balanced equation, and converts the resulting moles of product back to a mass. The output — theoretical yield — is exactly the number a percent yield calculator needs as its theoretical yield input, so the two tools chain together naturally.
Worked example 1 — thermite reaction
Given: 2 Al + Fe₂O₃ → Al₂O₃ + 2 Fe. You start with 10.0 g of Al (M = 26.98 g/mol), the limiting reactant. Find the theoretical yield of Fe (M = 55.85 g/mol).
A 1:1 mole ratio here means moles of product equal moles of reactant — the coefficients happen to match.
Worked example 2 — ammonia synthesis
Given: N₂ + 3 H₂ → 2 NH₃. You start with 15.0 g of H₂ (M = 2.016 g/mol), the limiting reactant. Find the theoretical yield of NH₃ (M = 17.03 g/mol).
Here the coefficients differ (3 vs 2), so the mole ratio noticeably shrinks the moles of product below the moles of reactant.
How theoretical yield is calculated by reaction type
The core three-step chain (mass → mol → mol → mass) is identical; only the mole ratio changes.
| Reaction type | Example | Mole ratio (product:reactant) |
|---|---|---|
| 1:1 stoichiometry | 2 Al + Fe₂O₃ → Al₂O₃ + 2 Fe (Fe:Al) | 2:2 = 1.00 |
| Product ratio < 1 | N₂ + 3 H₂ → 2 NH₃ (NH₃:H₂) | 2:3 = 0.667 |
| Product ratio > 1 | 2 H₂ + O₂ → 2 H₂O (H₂O:H₂) | 2:2 = 1.00 |
| Decomposition | CaCO₃ → CaO + CO₂ (CaO:CaCO₃) | 1:1 = 1.00 |
The mole ratio is always coefficient of product ÷ coefficient of the reactant you started from — read straight from the balanced equation.
Where theoretical yield actually matters
🏭 Industrial process design
Chemical engineers calculate theoretical yield at the design stage to size reactors, estimate raw-material feed rates, and set production targets before a single batch is ever run.
💊 Pharmaceutical batch planning
Before scaling up a drug synthesis, chemists calculate theoretical yield for every step to forecast how much active ingredient a batch of starting material can possibly produce, which drives costing and scheduling.
🔬 Lab report grading
Instructors compare a student's reported yield against the correctly calculated theoretical yield to check both the student's stoichiometry and their lab technique — an error here throws off every yield calculation downstream.
Common misconceptions
"Theoretical yield is just whatever number you plug into a yield formula."
Theoretical yield is itself calculated — from the limiting reactant's mass, its molar mass, the mole ratio from the balanced equation, and the product's molar mass. It is not a given, it is derived.
"You can use either reactant's mass to calculate theoretical yield."
Only the limiting reactant determines theoretical yield. Using the excess reactant overstates how much product could actually form, because the limiting reactant runs out first.
"The mole ratio is always 1:1."
The mole ratio is coefficient of product ÷ coefficient of reactant from the balanced equation, and is only 1:1 when those coefficients happen to match — as in worked example 1, but not example 2.
"Theoretical yield can be achieved in the lab with careful technique."
Theoretical yield assumes 100% conversion with zero losses — an idealized ceiling. Real reactions lose product to side reactions, incomplete conversion and purification, so actual yield is always at or below it.
Formula sources & further reading
The formulas here are standard, traceable to:
- • OpenStax, Chemistry 2e — Chapter 4.4, Reaction Yields (free, peer-reviewed). openstax.org
- • Brown, LeMay & Bursten, Chemistry: The Central Science — Chapter 3.6–3.7, Stoichiometric Calculations and Limiting Reactants.
- • Zumdahl & Zumdahl, Chemistry — Chapter 3, Stoichiometry, section on calculating theoretical yield.
Theoretical yield = (mass ÷ molar mass of reactant) × (coeff product ÷ coeff reactant) × molar mass of product. Use the limiting reactant's mass. Results are rounded for display.
How to use this calculator
Enter reactant data
Mass (g) and molar mass (g/mol) of the limiting reactant.
Enter coefficients
Reactant and product coefficients from the balanced equation.
Enter product molar mass
g/mol of the product you are forming.
Related tools
Frequently asked questions
What is theoretical yield?
Theoretical yield is the maximum mass of product a reaction can form, calculated from the limiting reactant using stoichiometry, assuming complete conversion with no losses whatsoever.
How do you calculate theoretical yield?
Convert the limiting reactant's mass to moles (mass ÷ molar mass), convert to moles of product using the mole ratio from the balanced equation (coefficient of product ÷ coefficient of reactant), then convert moles of product to mass (moles × molar mass of product).
Why do I need a balanced equation first?
The mole ratio between reactant and product comes directly from the coefficients in the balanced equation. An unbalanced equation gives the wrong ratio and therefore the wrong theoretical yield — balance it first, for example with a chemical equation balancer.
Is theoretical yield the same as actual yield?
No. Theoretical yield is the calculated ideal maximum from stoichiometry. Actual yield is what you actually measure after running the reaction and purifying the product — it is almost always lower, due to side reactions, incomplete conversion and purification losses.
What if I have two reactants — which one do I use?
Use the limiting reactant — the one that runs out first and caps how much product can form. If you are not sure which reactant is limiting, use a limiting reagent calculator first to identify it, then feed its mass into this calculator.