Gas Volume at STP Calculator
The volume an amount of gas occupies at standard conditions — from moles or from a mass and molar mass — with the molar volume for the standard you choose.
One mole of any ideal gas fills the same volume at a given temperature and pressure: 22.
How the gas volume at stp calculator works
One mole of any ideal gas fills the same volume at a given temperature and pressure: 22.71 L at IUPAC STP (0 °C, 1 bar), 22.41 L at the older 0 °C and 1 atm, and 24.79 L at SATP (25 °C, 1 bar). Multiply moles by the molar volume; for a mass, divide by the molar mass first. Real gases deviate by under 1% at these conditions.
Formula: V = n × V_m; n = mass ÷ M
Worked examples
| Inputs | Volume | Note |
|---|---|---|
| 2 mol at STP | 45.422 L | 45.42 L |
| 64 g of O₂ at 1 atm | 44.828 L | 44.83 L |
| 44 g of CO₂ at SATP | 24.79 L | 24.79 L |
FAQFrequently asked questions
Why are there two STPs?
IUPAC redefined standard pressure from 1 atm (101.325 kPa) to 1 bar (100 kPa) in 1982, moving the molar volume from 22.41 to 22.71 L. Many textbooks still use 22.4; check which your course expects.
Does the gas matter?
Not for an ideal gas — helium, oxygen and carbon dioxide all occupy the same volume per mole. Real gases differ slightly (CO₂ is about 0.6% smaller at 0 °C); the molar mass only matters when you start from a mass.
What about other temperatures and pressures?
Use the ideal gas law calculator: V = nRT ÷ P. STP and SATP are just the two conditions everyone agrees to quote.
How do I go from volume to moles?
Divide the volume by the molar volume: 10 L at STP is 10 ÷ 22.71 = 0.44 mol. Enter the moles that gives to get the mass with the molar mass.
Where these figures come from
- IUPAC — Standard atomic weights (2021 conventional values) — the molar-mass table
- NIST — CODATA 2018 fundamental physical constants — Avogadro constant, gas constant, speed of light
- NIST Chemistry WebBook — thermochemical data
- National Institute of Standards and Technology — the US measurement and reference-data authority
Last checked: September 2026. Atomic masses are the IUPAC conventional values; constants are CODATA 2018; equations are the standard textbook forms.