About the Molar Volume Calculator
This molar volume calculator finds the volume one mole of an ideal gas occupies, Vm = RT/P, and uses it to convert between moles and liters. Pick a standard condition — STP at 1 atm (22.414 L/mol), IUPAC STP at 1 bar (22.711 L/mol), SATP or NTP — or enter your own temperature and pressure in any common unit.
It is a quick tool for stoichiometry problems that involve gases, for lab work collecting gas over a reaction, and for converting cylinder or balloon volumes into amounts of substance. Add a molar mass to also get the mass of gas and its density under those conditions.
Be careful which “STP” your course uses: many US textbooks still use 0 °C and 1 atm (22.4 L/mol), while IUPAC has defined standard pressure as 1 bar since 1982 (22.7 L/mol). Results assume ideal-gas behaviour, which is accurate to within about 1% for most gases near room conditions.
With the default inputs, the answer is 44.8279. Change any value above to recalculate instantly.
How to use the molar volume calculator
- 1Choose whether to convert moles to volume or volume to moles.
- 2Enter the amount of gas in moles or the volume in liters.
- 3Select STP, IUPAC STP, SATP, NTP or enter your own temperature and pressure.
- 4Optionally enter a molar mass to get the mass and density of the gas.
Formula and method
From the ideal gas law PV = nRT, the volume per mole is Vm = RT/P, independent of which gas it is. With R = 8.314462618 J/(mol·K), T in kelvin and P in pascals, Vm comes out in m³/mol, which the calculator multiplies by 1,000 to give liters per mole. At 273.15 K and 101.325 kPa this is 22.414 L/mol; at 273.15 K and 100 kPa it is 22.711 L/mol.
Multiplying moles by Vm gives the gas volume, and dividing a volume by Vm gives moles. If you supply a molar mass, mass = n × M and density = M ÷ Vm. Real gases differ slightly from ideal behaviour, most noticeably at high pressure or near their condensation point.
- Vm
- Molar volume (L/mol)
- R
- Molar gas constant, 8.314462618 J/(mol·K)
- T
- Absolute temperature (K)
- P
- Absolute pressure (Pa)
- n
- Amount of gas (mol)
Worked examples
2 mol of CO₂ at STP (0 °C, 1 atm)
At 273.15 K and 101.325 kPa, Vm = 22.414 L/mol, so 2 mol occupies 44.83 L. With M = 44.01 g/mol that is 88.02 g of CO₂ at a density of 1.964 g/L.
10 L of gas at SATP (25 °C, 1 bar)
At SATP, Vm = 8.314 × 298.15 ÷ 100,000 × 1,000 = 24.79 L/mol. Dividing 10 L by 24.79 L/mol gives 0.4034 mol.
1 mol of O₂ at body temperature and 740 mmHg
740 mmHg is 98.66 kPa and 37 °C is 310.15 K, so Vm = 8.314 × 310.15 ÷ 98,659 × 1,000 = 26.14 L/mol. Oxygen’s density there is 32 ÷ 26.14 = 1.224 g/L.
Frequently asked questions
What is the molar volume of a gas at STP?+
At 0 °C and 1 atm (101.325 kPa) one mole of an ideal gas occupies 22.414 L. Under the IUPAC definition of STP, 0 °C and 1 bar (100 kPa), it occupies 22.711 L.
Why does my textbook say 22.4 L but another says 22.7 L?+
They use different standard pressures. 22.4 L/mol corresponds to 1 atm, the older convention still common in US courses; 22.7 L/mol corresponds to 1 bar, the IUPAC standard since 1982. Use whichever your course or exam specifies.
How do I convert moles of gas to liters?+
Multiply the number of moles by the molar volume at your conditions: V = n × Vm. At STP (1 atm), 0.5 mol × 22.414 L/mol = 11.21 L.
Is molar volume the same for every gas?+
For an ideal gas, yes — Avogadro’s law says equal volumes at the same temperature and pressure contain equal numbers of molecules. Real gases differ slightly: N₂ and O₂ deviate by about 0.1% or less near room conditions, and CO₂ by roughly 0.5–0.7% because its molecules attract each other more strongly.
What is SATP?+
Standard ambient temperature and pressure is 25 °C (298.15 K) and 1 bar. The molar volume of an ideal gas at SATP is 24.790 L/mol, a handy value for room-temperature lab calculations.