ChemBench

Avogadro's Law Calculator

More moles, more volume — same ratio.

Initial volume (L)

Initial moles

Final moles

Final volume

10 L

V₁/n₁ = V₂/n₂

What you entered

Initial volume (L): 5Initial moles: 1Final moles: 2

1
V₂ = V₁n₂ ÷ n₁
(5 × 2) ÷ 1= 10

Result

Final volume: 10 L

Adding moles to reach 2 total expands the gas to 10L.

Avogadro's law: volume against amount of gas

V1/n1 = V2/n2. At fixed temperature and pressure, volume is directly proportional to the number of moles, whatever the gas is.

Initial volume	Initial moles	New moles	New volume
22.4 L	1	2	44.800 L
22.4 L	1	0.5	11.200 L
11.2 L	0.5	1	22.400 L
10 L	2	3	15.000 L
5 L	1	4	20.000 L

Equal volumes of any two gases at the same temperature and pressure contain equal numbers of molecules. Hydrogen and xenon behave identically here despite a 65-fold difference in molar mass.

Equal moles, equal volume

At the same temperature and pressure, equal volumes of any gas contain the same number of moles — this is the basis for why gas volume scales directly and linearly with mole count.

The foundation of molar volume

This law is why '22.4 liters per mole at STP' is a single constant that works for any ideal gas, regardless of what the gas actually is.

Frequently asked questions

I have 1.5 mol of gas occupying 33.6 L at STP — if I add 0.5 mol more gas, what is the new volume?

V2 = V1 × n2/n1 = 33.6 × 2.0/1.5 = 44.8 L. Adding more moles proportionally increases volume at constant T and P.

Why does 1 mol of any gas occupy the same volume at STP?

Avogadro's law says equal moles of any ideal gas at the same T and P occupy the same volume. At STP (0°C, 1 atm) that volume is 22.4 L regardless of whether the gas is helium, nitrogen, or CO2.

How is Avogadro's law related to the ideal gas law?

It is the special case of PV = nRT where both P and T are constant. The ratio V/n = RT/P becomes a fixed constant, so volume scales linearly with moles.