Avogadro's Law Calculator
Volume and moles at constant temperature and pressure.
Work out Avogadro's Law. Volume and moles at constant temperature and pressure. Kelvin conversion handled for you.
V₂
20 L
2× the starting value
Equal volumes of any two gases at the same temperature and pressure hold equal numbers of molecules. That was Avogadro's 1811 hypothesis, and it took half a century to be accepted, because it implied elemental gases were diatomic when everyone assumed they were single atoms. The practical consequence is that gas volumes behave like mole ratios directly: two litres of hydrogen react with one of oxygen because the equation says 2:1, with no molar mass arithmetic in between. Only true at constant temperature and pressure — the molar volume is 22.414 L at 0 °C and 1 atm, but 24.055 L at 20 °C.
How the Avogadro's Law Calculator works
Solve V₁/n₁ = V₂/n₂ for volume or amount of gas. The law is why gas volumes can be used as mole ratios directly — two litres of hydrogen react with one of oxygen because the equation says 2:1, with no molar mass arithmetic needed in between.
Also known as: volume mole ratio calculator · v1/n1 = v2/n2 calculator · molar volume of a gas calculator · avogadro's law formula
Frequently asked questions
What is Avogadro's law?
Equal volumes of any gases, at the same temperature and pressure, contain equal numbers of molecules. So volume is proportional to moles: V₁/n₁ = V₂/n₂.
What is molar volume?
The volume one mole of gas occupies — 22.414 L at 0 °C and 1 atm, or 24.055 L at 20 °C. It is the same for every gas, which is the direct consequence of this law.
Why was Avogadro's hypothesis rejected for fifty years?
Because it implied elemental gases were diatomic when chemists assumed they were single atoms. It took Cannizzaro's work in 1860 to show that accepting it resolved the contradictions in atomic weights rather than creating them.
Does this work for gas mixtures?
Yes. The law counts molecules, not species, so a mixture behaves as the total number of moles regardless of what those moles are. That is also why Dalton's law of partial pressures works.
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