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Chemistry Tools · Updated October 21, 2026 · Reviewed by FormatFlow Editorial

Limiting Reactant Calculator

You can find the limiting reactant by comparing moles divided by coefficient for two or more reactants, then get the theoretical yield of a chosen product and the leftover amounts.

Runs in your browserFree · No sign-up · No watermark
REACTANTS → YIELDRuns in your browser
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Everything runs locally in this tab. No file is uploaded while the tool loads.

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How files are handled

At a glance

Works with
REACTANTS → YIELD
Processing
In your browser
Price
Free, no account
Updated
October 21, 2026
All Chemistry Tools

About Limiting Reactant Calculator

When two reactants are mixed, the reaction stops when the first one runs out. That reactant is the limiting reagent, and it decides how much product can form; the other reactants are in excess and some of each is left over.

This calculator balances the equation, converts each reactant amount to moles, divides by that reactant's coefficient and compares the ratios. It then works out the theoretical yield of a chosen product and the leftover amount of every excess reactant, with the working shown line by line.

What this tool does

The details that matter when you use Limiting Reactant Calculator for real work.

  • Compares every reactant

    Enter amounts for two or more reactants and the tool computes moles divided by coefficient for each one, which is the direct test for a limiting reagent.

  • Auto-balanced equation

    Type the reaction as written and the shared integer solver supplies the smallest whole-number coefficients before any comparison starts.

  • Mass or moles per reactant

    Each reactant row can be entered in grams with its molar mass or directly in moles, and the formula molar mass is offered as a one-click fill.

  • Theoretical product yield

    Choose a product and the calculator scales from the limiting amount through the coefficient ratio to give the product's moles and mass.

  • Leftover excess amounts

    Every non-limiting reactant gets a consumed amount and a leftover amount in moles and grams, so nothing is left implicit.

  • Step-by-step working

    The conversion steps, ratio comparison, limiting callout and yield calculation are printed so a hand check is quick.

How to use Limiting Reactant Calculator

No account, no installation — the whole job happens in this browser tab.
  1. 01

    Enter the equation

    Type the balanced or unbalanced reaction with ->, → or = between the sides and + between formulas.

  2. 02

    Give at least two reactant amounts

    Choose each reactant from the picker and enter its starting mass with a molar mass, or its amount in moles.

  3. 03

    Pick the product

    Select which product's theoretical yield you want; only species from the right-hand side are listed.

  4. 04

    Read the limiting reagent

    The reactant with the smallest moles divided by coefficient is the limiting reagent, and it is highlighted in the comparison table.

  5. 05

    Check the yield and leftovers

    Review the theoretical product yield, the leftover excess amounts and the step-by-step working for a hand check.

How this tool works

Works with
REACTANTS → YIELD
Processing
Client-side, in your browser. Nothing is uploaded.
Requirements
Chrome, Edge, Firefox or Safari · JavaScript enabled

Limitations worth knowing

  • Assumes the reaction goes to completion along the balanced ratio with a 100% theoretical yield and no side reactions.
  • Requires at least two reactants in a neutral, balanceable molecular equation; ionic and redox charge balancing is not supported.
  • All species are assumed to react in one step, so parallel reactions, equilibria and real reaction rates are outside its scope.

Privacy and file handling

Equations and amounts are processed in your browser tab. Nothing you enter is uploaded, stored or logged, and the calculator makes no network request.

Read the full privacy policy

Limiting Reactant Calculator FAQ

Short, direct answers to the questions people ask before using this tool.
How do I find the limiting reactant in a reaction?
Convert every reactant amount to moles, divide each by its coefficient in the balanced equation, and compare the results. The smallest quotient identifies the limiting reactant; in 2H2 + O2 -> 2H2O, H2 has a coefficient of 2 in the ratio.
What is the difference between a limiting reactant and an excess reactant?
The limiting reactant is completely consumed first and therefore determines how much product can form. An excess reactant is present in a larger stoichiometric amount, so some of it remains unreacted when the limiting reactant runs out.
Does the limiting reactant always have the smallest mass?
No. The comparison is in moles divided by coefficient, not in grams. A dense or heavy compound can have a large mass and still run out first if its molar mass or coefficient is large, which is why the mass must be converted to moles first.
Why is the theoretical yield based on the limiting reactant?
The reaction stops once the limiting reactant is gone, no matter how much of the other reactants remain. The balanced coefficients convert the limiting amount into the maximum possible product amount, which is the theoretical yield.
What if two reactants have the same moles divided by coefficient?
Then they run out together and both are limiting; the reaction consumes each exactly to completion at the same point. The calculator flags the tie and uses the first reactant as the limiting one, which gives the same theoretical yield.
Does this calculator include percent yield?
No. It reports the theoretical yield assuming complete reaction along the balanced ratio. To compare with what you actually collected, open the theoretical yield calculator's percent mode and divide the actual mass by this theoretical mass.
Can I mix grams and moles for different reactants?
Yes. Each reactant row has its own unit switch, so one reactant can be entered as a mass with its molar mass while another is entered directly in moles. Both are converted to moles before the ratio comparison.
Why does the calculator need a balanced equation?
The coefficients supply the mole ratio, without which moles divided by coefficient has no meaning. The tool balances the equation automatically when needed and explains why if the equation cannot be balanced.

Background reading

Format guides that explain the trade-offs behind Limiting Reactant Calculator.