Avogadro's Law Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/8/2026
Avogadro's law states that V₁/n₁ = V₂/n₂ at constant temperature and pressure, where V is volume and n is amount of substance. For 10 L at 2 mol, going to 5 mol, the new volume is 25 L.
Explanation
Avogadro's law states that, at constant temperature and pressure, the volume occupied by a gas is directly proportional to its amount of substance (the number of moles), regardless of the nature of the gas: equal volumes of different gases, under the same temperature and pressure conditions, contain the same number of molecules. This law is what defines the standard molar volume, the best-known reference being that one mole of gas occupies about 22.4 liters under standard temperature and pressure conditions (0°C, 1 atm). This law is a special case of the full ideal gas law (PV = nRT), obtained by fixing both temperature and pressure, exactly on the same principle as Boyle's law (temperature fixed) or Charles's law (pressure fixed): each isolates a pair of variables by holding the other two constant. This calculator typically answers the question: if I change the amount of gas (for example by adding or removing material in a closed flask, without changing temperature or pressure), what final volume will I get? For the full relationship between pressure, volume, amount of substance, and temperature, see our ideal gas law calculator.
Example: 10 L at 2 mol, amount increased to 5 mol
Inputs
Initial volume (V₁): 10 L. Initial amount (n₁): 2 mol. Final amount (n₂): 5 mol.
Calculation
Final volume = 10 × 5 ÷ 2 = 25 L.
Result
Going from 2 to 5 mol at constant temperature and pressure, the volume goes from 10 L to 25 L.
Frequently asked questions
Where does the value of 22.4 L for one mole of gas come from?
This value, often called the standard molar volume, follows directly from the ideal gas law (PV = nRT) applied to 1 mole under standard temperature and pressure conditions (0°C, i.e. 273.15 K, and 1 atm). It holds for any gas assumed to be ideal under these specific conditions — it changes if the reference temperature or pressure changes.
Does this law apply to a mixture of several different gases?
Yes, Avogadro's law applies regardless of the nature of the gas or gases present: what matters is the total number of moles of gas particles, not their chemical identity. A mixture of two different gases therefore occupies the same volume as a pure gas, for the same total amount of substance, temperature, and pressure.
What happens if temperature or pressure change at the same time as the amount of substance?
This law no longer applies directly in that case, since it assumes constant temperature and pressure. For a transformation where several variables change simultaneously, you need to use the full ideal gas law (PV = nRT), which relates all four quantities at once — see our ideal gas law calculator.