Avogadro's Law Calculator
Avogadro's law states that, at constant temperature and pressure, the volume of a gas is directly proportional to the number of moles. This means doubling the number of moles of gas doubles its volume. The relationship V1/n1 = V2/n2 can be solved for any unknown when the other three values are known. This calculator is used in stoichiometry to determine the volume of gas produced in a chemical reaction, and in laboratory settings to relate measured gas volumes to molar quantities. Volume can be in any unit (L, mL, m^3) as long as both V1 and V2 use the same unit.
Avogadro's law formula
V1 / n1 = V2 / n2
Solve for the unknown: V2 = V1 * n2 / n1; n2 = n1 * V2 / V1; V1 = V2 * n1 / n2; n1 = n2 * V1 / V2. Temperature and pressure must remain constant between states 1 and 2.
Key reference values
- At STP (0 degrees C, 1 atm): 1 mol of ideal gas occupies 22.414 L.
- At NIST standard conditions (20 degrees C, 1 atm): 1 mol occupies 24.055 L.
- Avogadro's number: 6.02214076 x 10^23 entities per mole (exact by NIST/SI definition since 2019).
Frequently asked questions
What is Avogadro's law?
Avogadro's law states that equal volumes of all ideal gases at the same temperature and pressure contain the same number of molecules. Mathematically, V1/n1 = V2/n2, meaning volume is directly proportional to the number of moles at constant temperature and pressure.
What is the molar volume of a gas at STP?
At standard temperature and pressure (0 degrees C, 1 atm), one mole of any ideal gas occupies 22.414 liters. At NIST standard conditions (20 degrees C, 1 atm), the molar volume is 24.055 liters per mole.
What does Avogadro's law assume?
The law assumes ideal gas behavior (negligible intermolecular forces and molecular volumes), constant temperature, and constant pressure. Real gases at moderate conditions closely follow this relationship.
How is Avogadro's law used in chemistry?
It is used to find the volume of gas produced in a reaction when the moles of product are known, to compare gas volumes in balanced equations (mole ratios equal volume ratios), and to calculate molar volumes.
What is Avogadro's number?
Avogadro's number (6.022 x 10^23 mol^(-1)) is the number of molecules in one mole of any substance. It is the proportionality constant that relates macroscopic amounts to individual particle counts.
Official sources
- NIST: Avogadro Constant (NIST CODATA).
- OpenStax University Chemistry: 9.2 Relating Pressure, Volume, Amount, and Temperature.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.