Stoichiometry Calculator
Convert an amount of one species into the amount of another using the mole ratio.
What is Stoichiometry?
Stoichiometry is the arithmetic of a balanced equation: the coefficients tell you the ratio in which substances react, so an amount of one species determines the amount of every other. It is the single most used calculation in introductory chemistry.
How it works
The equation you enter is balanced first, so you do not need to supply coefficients. Then the given amount is converted to moles if it was a mass, multiplied by the ratio of coefficients (target ÷ given) and converted back to a mass if you want grams. Each of those three steps is shown separately because they are the three places marks are lost.
- Enter what you know. Every field recalculates as you type — there is no submit button. Leave the quantity you want blank and the page solves for it.
- Read the answer and the working. The result appears above the fold; underneath it is the formula with your numbers substituted, so the arithmetic can be checked rather than trusted.
- Check the units and the size. Units are shown on every value and selectable per field, so a result in kJ, kPa or km/h is converted rather than assumed. Sanity-check the magnitude against a known landmark such as 1 g/cm³ for water.
Examples
A textbook problem with a known answer
Every tool here is checked against standard example problems — the molar mass of C6H12O6 is 180.16 g/mol, and free fall from 20 m takes about 2.02 s at g = 9.8 m/s².
A result you want to reason backwards from
Leave the quantity you already know blank instead: given the final answer, most tools recover the starting value — the mass needed for a target concentration, or the height a fall must have had.
Common mistakes
Forgetting that a formula is only as good as its subscripts
H2O and H2O2 are different compounds. The formula field shows its parse — element by element — so a mis-typed subscript is visible before it reaches the arithmetic.
Mixing units in the middle of a calculation
The most common source of a wrong answer is a value in grams next to a formula expecting kilograms, or Celsius next to a gas constant expecting kelvin. This category converts on the way in and labels what it used.
Frequently asked questions
Do I need to balance the equation first?
No — the calculator balances it for you and shows the balanced form it used, so a wrong ratio cannot come from an unbalanced input.
What is a mole ratio?
The ratio of the coefficients of the two species in the balanced equation. For 2H2 + O2 → 2H2O, every 2 moles of hydrogen produce 2 moles of water, so the ratio is 2:2, or 1:1.
Can the answer be a mass instead of moles?
Yes. Enter the given amount in grams or moles and the result gives both — moles for the next step of a calculation, grams for what you would weigh out.