Limiting Reagent Calculator
Find the limiting reactant from equation stoichiometry and amounts.
Enter a reaction and the amount of each reactant you have. The equation is balanced automatically, every amount is converted to moles, and moles ÷ coefficient identifies which reactant runs out first — along with the theoretical yield of every product and how much excess is left over.
Balanced equation
Enter what you have for each reactant
Comparing raw masses is the classic mistake: always divide moles by the balanced coefficient before deciding which reactant runs out.
How to Use the Limiting Reagent Calculator
1
Enter the reaction. Type the chemical equation; it is balanced automatically and the coefficients are used for the comparison.
2
Enter what you have. Give the amount of each reactant in grams or moles. At least two reactants are needed to make a comparison.
3
Read the comparison. The table shows moles divided by coefficient for every reactant, marks the limiting one, and reports the theoretical yield of each product and the excess left over.
What is the Limiting Reagent Calculator?
The limiting reagent calculator compares the available moles of each reactant against the balanced equation's coefficients to find which reactant runs out first. It reports the limiting reagent, the theoretical yield of each product, and how much excess reactant remains.
The moles-divided-by-coefficient comparison is one of the most tested skills in general chemistry and the most common source of errors in yield problems. Seeing the comparison laid out for every reactant side by side is the fastest way to internalize the method.
Common Uses
- Identify the limiting reactant from starting amounts
- Calculate theoretical yield for a reaction
- Find leftover excess reagent after completion
- Set up percent yield problems correctly
How to Solve It by Hand
Manual calculation is still important: identify the known variables, convert units before substitution, apply the equation, and check whether the result is chemically reasonable. The most common mistakes are inconsistent units, constants rounded too early, and skipping the interpretation step.
Practice Prompt
Try changing the default values and ask the lower-right chemistry chat why the result increased or decreased. That turns the calculator from a number machine into a study loop.
Convert each reactant's amount to moles, then divide those moles by that reactant's coefficient in the balanced equation. The reactant with the smallest result runs out first and is the limiting reagent. Comparing raw masses or raw moles without dividing by the coefficient is the most common mistake.
Because molar masses and coefficients differ. 8 g of H2 is 4 moles while 28 g of N2 is only 1 mole, so the lighter reactant can easily be in excess. Only the moles-to-coefficient ratio tells you which reactant limits the reaction.
Multiply the reaction extent (limiting moles divided by its coefficient) by the product's coefficient to get moles of product, then multiply by the product's molar mass. The calculator reports this for every product in the equation.
Subtract the moles actually consumed from the moles supplied. Consumed moles equal the reaction extent times that reactant's coefficient. The results table shows the leftover amount in both moles and grams.
Yes. Type an unbalanced reaction such as Al + Fe2O3 = Al2O3 + Fe and it is balanced first, then the coefficients are used for the limiting reagent comparison.