How to Use the Stoichiometry Calculator
Follow the controls in order for a manual calculation. The examples use a shorter path.
- Enter a balanced equation in Balanced chemical equation, such as
2H2 + O2 -> 2H2O. - Click Parse equation. The tool validates the equation and fills Known species and Species to calculate.
- Choose the known species, enter Known quantity, and select Known unit.
- Choose the target species and select Result unit.
- Click Calculate to show the result and intermediate steps.
To use an example, click an example equation. It fills the equation and inputs, selects the species, parses the equation, and calculates immediately. Use Copy result for plain text or Download result (.txt) to save the result. Click Reset to clear the equation, quantity, selections, errors, and result.
Inputs, Equation Format, and Supported Units
- Put + between species and use a reaction arrow such as
->,-->,=>,==>,<=>, or=. Coefficients may be positive integers or decimals placed before formulas. - Formulas may include nested parentheses and square brackets. The equation needs at least one species on each side.
- Known unit and Result unit each support
mg,g,kg, andmol.
How the Calculation Works
The calculator uses the coefficients in your balanced equation:
moles(known) = mass(known) / molar mass(known)when the known value is a mass.moles(target) = moles(known) × coefficient(target) / coefficient(known).- It converts target moles to the selected mass unit with the target molar mass. A
molresult skips that conversion.
The result shows the formula, balanced equation, coefficients, molar masses, mole ratio, intermediate values, and final value. Molar masses use the built-in atomic-weight table.
Validation and Error Cases
- The parser rejects unknown element symbols, malformed formulas, and unbalanced parentheses. It also rejects duplicate formulas in the parsed species list because the selection would be ambiguous.
- The tool counts atoms on both sides and rejects an unbalanced equation. It checks balance but does not balance equations.
- Known quantity must be a positive decimal greater than
0and no greater than1e12. - The known and target species must be different. Non-finite conversions or results are rejected.
Assumptions and Limitations
The calculation uses only the mole ratio in the entered balanced equation and assumes the reaction proceeds as written to completion. It does not determine limiting reagents, side reactions, reaction conditions, equilibrium behavior, or percent yield. It does not infer missing coefficients or formulas, and its output is not certified laboratory or professional advice.
Privacy and Calculation Handling
The calculator script performs the stoichiometry calculation locally in your browser and does not upload the equation or values you enter. This statement applies to the calculator's calculation script, not to other page resources.
Frequently Asked Questions
What is the stoichiometry formula this calculator uses?
It converts the known quantity to moles using moles = mass / molar mass, applies the mole ratio from the balanced equation's coefficients (moles of target = moles of known x coefficient of target / coefficient of known), then converts the result back to your chosen unit using mass = moles x molar mass.
Does this tool balance chemical equations for me?
No. You must enter an already-balanced equation. The calculator checks that atom counts match on both sides and rejects the equation with an explicit error if they do not - it does not guess coefficients or balance the equation for you.
What units does this calculator support?
The known quantity and the calculated result can each independently use milligrams (mg), grams (g), kilograms (kg), or moles (mol). Mass units are converted to and from moles using the molar mass computed from each species' formula and the built-in atomic-weight table.
Does this account for limiting reagents or reaction yield?
No. The calculation assumes the reaction proceeds exactly as written to completion using only the mole ratio between the known and target species. It does not determine the limiting reagent among multiple reactants, side reactions, or a real-world percent yield.