How to use the Stoichiometry Calculator
Start with a balanced reaction such as 2H2 + O2 -> 2H2O. The calculator checks the atom totals, lets you choose the known and target species, and shows each conversion used to reach the result. The known quantity and result can each be in milligrams, grams, kilograms, or moles.
- Enter the balanced reaction in Balanced chemical equation, such as
2H2 + O2 -> 2H2O. - Click Parse equation. The calculator checks the equation and fills the species menus.
- Choose the known formula in Known species, enter Known quantity, and select Known unit.
- Choose a different formula in Species to calculate, then select Result unit.
- Click Calculate to display the result and its calculation steps.
The example equation buttons fill the equation, quantity, unit, and species selections, then calculate immediately. Once a result appears, Copy result copies the plain text to the clipboard. Download result (.txt) saves the same text as a file, and Reset clears the current calculation.
How the mole ratio calculation converts units
For a mass value, the calculator converts the known unit to grams and divides by the known species' molar mass. It then multiplies the moles by the target coefficient divided by the known coefficient. Finally, it converts the target moles to the selected Result unit. When Result unit is moles, the final mass conversion is skipped.
2H2 + O2 -> 2H2O
Known species: H2 (reactant)
Known quantity: 2 g
Species to calculate: H2O (product)
Result: 17.872 g H2OThe result includes the balanced equation, the coefficient ratio, molar masses, intermediate values, and final value. The calculator gets each molar mass from its built-in atomic-weight table.
Equation formats the Stoichiometry Calculator accepts
- Separate species with
+. The reaction arrow can be->,-->,=>,==>,<=>, or=. - Put a positive integer or decimal coefficient before a formula. Formulas can contain element symbols, numbers, parentheses, and square brackets, including a grouped formula such as
Al2(SO4)3. - Put at least one species on each side. Every formula must use element symbols from the built-in atomic-weight table.
What the calculator checks and leaves out
- The equation must already be balanced. The parser counts each element on both sides and rejects a mismatch. It does not find missing coefficients.
- Known quantity must be a positive decimal no greater than
1e12. The known and target species must be different. - Unknown elements, malformed formulas, unbalanced parentheses, duplicate formulas, and non-finite results cause an error.
The calculation runs in your browser. The page contains no request that sends the equation or quantities you enter.
Examples with grouped formulas and mole ratios
Use 2H2 + O2 -> 2H2O to calculate a water quantity from a known hydrogen quantity. The coefficient ratio for H2O to H2 is 2 / 2. The equation N2 + 3H2 -> 2NH3 uses a different ratio and can return grams or moles.
For a grouped formula, enter the balanced reaction directly, such as 2Al + 3CuSO4 -> Al2(SO4)3 + 3Cu. The parser calculates the molar mass of Al2(SO4)3 before applying the coefficient ratio.
Choosing a related science calculator
Use the Science Calculators category to browse related calculations. Choose the Chemistry Calculator for limiting reagent, percent yield, pH, dilution, or several chemistry calculations. Choose the Molar Mass Calculator when you need the mass of one formula. Choose the Percent Yield Calculator when the actual and theoretical yields are already known.
Questions about stoichiometry calculations
How do I calculate stoichiometry from a balanced equation?
Enter the equation, click Parse equation, choose Known species and Species to calculate, enter Known quantity, and click Calculate. The calculator converts to moles, applies the coefficient ratio, and converts to Result unit.
Can a stoichiometry calculator balance my chemical equation?
No. Enter the balanced equation first. The calculator checks the atom totals and rejects the equation when the totals do not match.
What units can I use for a stoichiometry calculation?
Known unit and Result unit each support milligrams (mg), grams (g), kilograms (kg), and moles (mol). The calculator uses the selected species' molar mass when converting a mass value.
Does this calculate limiting reagent or percent yield?
No. It uses the mole ratio in the entered equation and assumes the reaction proceeds as written to completion. It does not determine the limiting reagent, side reactions, or percent yield.