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Chemistry Tools · Updated October 21, 2026 · Reviewed by FormatFlow Editorial

Gas Molar Volume Calculator

You can calculate a gas volume from moles or mass, find moles from a volume, and read the molar volume RT/P at any temperature and pressure using the ideal gas law.

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GAS → VOLUMERuns in your browser
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Everything runs locally in this tab. No file is uploaded while the tool loads.

This tool runs in your tab. Nothing is uploaded and no copy is stored.

How files are handled

At a glance

Works with
GAS → VOLUME
Processing
In your browser
Price
Free, no account
Updated
October 21, 2026
All Chemistry Tools

About Gas Molar Volume Calculator

One mole of an ideal gas occupies the same volume as any other gas at the same temperature and pressure, which is why a molar volume calculation works without knowing which gas is present. The volume follows directly from PV = nRT.

This calculator converts between moles or mass and gas volume at a chosen temperature and pressure, and reports the molar volume Vm = RT/P for those conditions. Standard conditions, room conditions and legacy STP are one click away, and every step is shown with the converted units.

What this tool does

The details that matter when you use Gas Molar Volume Calculator for real work.

  • Both calculation directions

    Find a volume from moles or from mass plus a formula, or find the moles and mass that a known gas volume contains at the chosen conditions.

  • Any common conditions

    Temperature in K or °C, pressure in kPa, atm, bar, mmHg or Pa, and volume in L, mL or m³, with conversions in the working.

  • Molar volume at a glance

    The result panel always shows Vm = RT/P, so you can compare the conditions with standard molar volume directly.

  • Condition presets

    IUPAC standard (273.15 K, 100 kPa), room conditions (298.15 K, 100 kPa) and legacy STP (273.15 K, 101.325 kPa) fill the fields in one click.

  • Mass through the formula parser

    Enter a formula such as O2 or CO2 to get its molar mass and convert between mass and moles without a separate lookup.

  • Worked steps

    The formula, substituted values, unit conversions and the final volume or mole amount are written out for a hand check.

How to use Gas Molar Volume Calculator

No account, no installation — the whole job happens in this browser tab.
  1. 01

    Choose the direction

    Pick volume from amount when you know moles or mass, or amount from volume when you know the gas volume and want moles.

  2. 02

    Set the conditions

    Enter a temperature and pressure, or click a preset for standard, room or legacy STP conditions, then adjust the units if you need to.

  3. 03

    Enter the known amount

    Type moles directly, or a mass with the gas formula so the molar mass comes from the formula parser.

  4. 04

    Read the result

    The big result and the summary show the volume or amount, the molar volume RT/P and the converted temperature and pressure.

  5. 05

    Check the working

    The step panel shows the conversions and the substituted ideal gas law, and notes that ideal behavior is assumed.

How this tool works

Works with
GAS → VOLUME
Processing
Client-side, in your browser. Nothing is uploaded.
Requirements
Chrome, Edge, Firefox or Safari · JavaScript enabled

Limitations worth knowing

  • Assumes ideal gas behavior, so compressibility and intermolecular forces are ignored; real gases deviate at high pressure and low temperature.
  • For gas mixtures the volume gives the total moles only; the composition is needed before a mixture mass can be calculated.
  • The result depends on the entered temperature and pressure, which must be positive and are not corrected for measurement or non-ideal effects.

Privacy and file handling

Temperatures, pressures, amounts and formulas are processed only in your browser tab. Nothing is uploaded, stored or logged, and the calculator makes no network request.

Read the full privacy policy

Gas Molar Volume Calculator FAQ

Short, direct answers to the questions people ask before using this tool.
What is molar volume?
Molar volume is the volume occupied by one mole of a gas, Vm = V/n, and for an ideal gas it is Vm = RT/P. At legacy STP (273.15 K, 101.325 kPa) it is 22.414 L/mol; at IUPAC standard (273.15 K, 100 kPa) it is 22.71 L/mol.
Why is 22.4 L per mole used at STP?
The familiar 22.4 L/mol comes from the older definition of STP as 273.15 K and 1 atm (101.325 kPa). With R = 8.314462618 J/(mol·K), RT/P gives 22.414 L/mol at those conditions, which is why textbooks round it to 22.4.
What is the difference between STP and SATP?
Legacy STP is 273.15 K and 101.325 kPa, giving 22.414 L/mol. SATP is 298.15 K and 100 kPa, giving 24.79 L/mol. IUPAC also defines standard conditions as 273.15 K and 100 kPa, which gives 22.71 L/mol, so the pressure matters as much as the temperature.
Does the identity of the gas affect the molar volume?
For an ideal gas, no: all gases have the same molar volume at a given temperature and pressure. Real gases deviate by a few percent, especially near condensation, so the identity only matters when the result needs real-gas accuracy.
How do I find moles from a gas volume?
Rearrange PV = nRT to n = PV/RT, with pressure in pascals, volume in cubic meters and temperature in kelvin. This calculator does the conversion for the units you enter and shows the substituted calculation.
Why must the temperature be in kelvin?
The ideal gas law uses an absolute temperature scale, so the gas constant and the volume are defined relative to zero kelvin. A temperature in °C must be converted by adding 273.15 before it enters PV = nRT.
Can I use this calculator for real gases?
It uses the ideal gas approximation, which is good for gases well above their boiling point and at moderate pressure. At high pressure or low temperature, attractive forces and molecular volume cause deviations, and an equation of state with a compressibility factor would be more accurate.
How do I convert °C to K?
Add 273.15 to the Celsius temperature: 25 °C becomes 298.15 K. The calculator accepts °C directly and performs the conversion before using the ideal gas law, so the same field can be used either way.

Background reading

Format guides that explain the trade-offs behind Gas Molar Volume Calculator.