Limiting Reactant Calculator
Find the limiting reactant from a chemical equation and the amount of each reactant in grams or moles. Auto-balances the equation, then reports theoretical yield for every product, how much of each excess reactant is left over, and percent yield from your actual yield.
Input
Reactants → products, separated by + and an arrow (->, →, or =). Coefficients are optional — the equation is re-balanced automatically. Symbols are case-sensitive.
One amount per reactant, comma-separated, in the same order as the equation.
The mass of product you actually collected — fill in to get the percent yield.
Which product (1 = first after the arrow) the actual yield refers to.
Output
| Reactant | Coef. | Molar Mass (g/mol) | Moles Given | Moles ÷ Coef. | Status | Left Over (mol) | Left Over (g) |
|---|---|---|---|---|---|---|---|
| No data yet | |||||||
| Product | Coef. | Molar Mass (g/mol) | Yield (mol) | Yield (g) |
|---|---|---|---|---|
| No data yet | ||||
More ways to use this tool
REST API
curl -X POST https://api.iotools.cloud/v1/tool/limiting-reactant-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"equation": "H2 + O2 -> H2O",
"amounts": "10, 64",
"unit": "g",
"actualYield": "65",
"yieldProduct": "1"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `limiting-reactant-calculator` tool (Limiting Reactant Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.
Embed widget
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src="https://iotools.cloud/embed/limiting-reactant-calculator/"
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<script src="https://iotools.cloud/embed.js" async></script>Drop this into your own page — free, no key required, just a link back.
| Cost per API/MCP call | From 5 credits |
|---|---|
| Need more credits? | View pricing |
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Guides
The Limiting Reactant Calculator finds which reactant runs out first in a chemical reaction, how much product that allows, and how much of every other reactant is left over. Type the equation, enter how much of each reactant you have in grams or moles, and the whole stoichiometry problem is worked out, step by step.
How to use it
- Type the chemical equation, e.g.
H2 + O2 -> H2O. Separate species with+and the two sides with->,→or=. You don't need to balance it first: the calculator balances it for you, and if you typed coefficients that don't balance, it replaces them. - Enter the reactant amounts, one per reactant, separated by commas and in the same order as the equation (
10, 64). - Pick the unit: grams or moles.
- Optionally enter the actual yield in grams, and which product it refers to, to get the percent yield.
Formulas follow the same rules as the Molar Mass Calculator. Element symbols are case-sensitive (Co is cobalt, CO is carbon monoxide), groups like Ca(OH)2 work, and so do hydrates like CuSO4·5H2O.
How the limiting reactant is found
For each reactant:
moles = grams ÷ molar mass
ratio = moles ÷ coefficient in the balanced equationThe reactant with the smallest ratio is limiting. That ratio is the reaction extent, meaning how many times the balanced reaction can run. Everything else follows from it:
- Theoretical yield of each product = extent × product coefficient (moles), × molar mass (grams).
- Left over of each excess reactant = moles given − extent × its coefficient.
If two reactants have the same ratio, the mixture is exactly stoichiometric. Both are marked limiting and nothing is left over.
Example
10 g of hydrogen and 64 g of oxygen:
Balanced: 2H2 + O2 → 2H2O
H2: 10 g ÷ 2.016 g/mol = 4.960 mol ÷ 2 = 2.480
O2: 64 g ÷ 31.998 g/mol = 2.000 mol ÷ 1 = 2.000 ← smallest, limiting
H2O: 2.000 × 2 × 18.015 = 72.06 g theoretical yieldAbout 0.96 mol (1.94 g) of hydrogen is left unreacted. If you actually collected 65 g of water, the percent yield is 90.2%.
What the results show
- Balanced equation, with a note in the steps if your coefficients were recalculated.
- Reactants table: coefficient, molar mass, moles, the moles ÷ coefficient ratio, limiting/excess status, and leftover amount in moles and grams.
- Theoretical yield for every product, not just one.
- Percent yield when you enter an actual yield.
Both tables can be copied or downloaded as CSV.
Limitations
Ionic equations with charges (Fe3+, e-) aren't supported, since the + would be read as a separator. Write them as neutral compounds instead. An equation that adds two independent reactions together can't be balanced uniquely, so split it into separate reactions.
FAQ
Is limiting reactant the same as limiting reagent?
Yes. Both terms mean the reactant that is completely consumed first and so caps the amount of product.
I only need the percent yield. Is there a simpler tool?
If you already know the theoretical yield, the Percent Yield Calculator takes just the two masses. To turn a mass into a concentration for solution reactions, use the Molarity Calculator.
Privacy
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