Can I solve for different variables?

Yes! This calculator supports reverse solving. You can solve for: Universal gas constant, Mass, Molar mass, Moles, Pressure, Temperature, Volume.

Molar mass of gas

Solve molar mass of gas relationships quickly using core chemistry formulas.

Formula shown6 inputs definedUpdated Nov 2025By Automated Chemistry GeneratorFree, no sign-up

Quick Summary

Use this when you need:

Identify an unknown gas from measured P–V–T data
Check whether collected gas was dry by comparing calculated molar mass
Teach how the ideal gas law links density and molar mass

You’ll need:Mass, Molar mass, Moles, Pressure, and 2 more

You’ll get:Universal gas constant

How this is calculated

Formula:

n = PV / (R T); M = mass / n

In plain language:

Using the ideal gas law, moles n equal pressure times volume divided by the gas constant R and temperature T; dividing the sample mass by n returns the experimental molar mass of the gas.

The formula is always visible so you can verify the math and explain your numbers to anyone who asks.

What these terms mean

Universal gas constant

Universal gas constant used in the calculation.

Mass

Mass used in the calculation.

Molar mass

Molar mass used in the calculation.

Moles

Moles used in the calculation.

Pressure

Pressure used in the calculation.

Temperature

Temperature used in the calculation.

Volume

Volume used in the calculation.

When to use this calculator

Identify an unknown gas from measured P–V–T data
Check whether collected gas was dry by comparing calculated molar mass
Teach how the ideal gas law links density and molar mass

Last updated: November 19, 2025

Molar mass of gas calculator explained

Collecting a gas sample and measuring its pressure, volume, temperature, and mass lets you determine its molar mass through the ideal gas law. This calculator applies $n = \\frac{PV}{RT}$ to find moles {moles}, then divides the measured mass {mass} by $n$ to report molar mass {molar_mass}.

Use it to confirm the identity of laboratory gases, check whether a sample is dry, or demonstrate how density and molar mass are connected.

How the conversion works

Starting from $PV = nRT$ :

n = \\frac{P V}{R T}, \\qquad M = \\frac{m}{n}

where $P$ is absolute pressure, $V$ is volume, $T$ is absolute temperature, $R$ is the universal gas constant, $m$ is mass, and $M$ is molar mass. The calculator keeps $R$ configurable so you can use $0.082057$ L atm mol $^{-1}$ K $^{-1}$ , $8.314$ J mol $^{-1}$ K $^{-1}$ , or another unit system.

Units and conversions

Quantity	Units	Notes
Pressure $P$	atm, bar, kPa	Convert gauge readings to absolute pressure.
Volume $V$	L, m $^3$	Must match the pressure unit and chosen $R$ .
Temperature $T$	K	Convert deg C to K by adding 273.15.
Gas constant $R$	depends on units	e.g., 0.082057 L atm mol $^{-1}$ K $^{-1}$ .
Mass $m$	g	Same unit appears in molar mass output.
Molar mass $M$	g/mol	$M = m / n$ .

Worked examples

Identify an unknown cylinder gas
$m = 0.845\\ \\text{g}$ , $P = 0.978\\ \\text{atm}$ , $V = 0.250\\ \\text{L}$ , $T = 295\\ \\text{K}$ , $R = 0.082057$ .

n = \\frac{0.978 \\times 0.250}{0.082057 \\times 295} = 1.01 \\times 10^{-2}\\ \\text{mol}

M = \\frac{0.845}{1.01 \\times 10^{-2}} = 83.7\\ \\text{g}\\,\\text{mol}^{-1}

The value suggests the gas could be SO $_2$ (64 g/mol) with moisture or another heavier species present; check for leaks or impurities.

Confirm density during gas evolution
$m = 1.52\\ \\text{g}$ collected at $P = 1.05\\ \\text{atm}$ , $V = 0.500\\ \\text{L}$ , $T = 330\\ \\text{K}$ .

n = \\frac{1.05 \\times 0.500}{0.082057 \\times 330} = 1.94 \\times 10^{-2}\\ \\text{mol}

M = \\frac{1.52}{1.94 \\times 10^{-2}} = 78.4\\ \\text{g}\\,\\text{mol}^{-1}

This matches benzene vapor (78.1 g/mol), confirming the sample is dry.

Tips and pitfalls

Correct for water vapor pressure if the gas was collected over water; subtract $P_{\\text{H}_2\\text{O}}$ from total pressure before applying the formula.
Always use absolute temperature; forgetting to convert deg C to K is the most common error.
For high-pressure or low-temperature data, apply a compressibility factor ( $Z$ ) or a real-gas equation of state to improve accuracy.
Maintain unit consistency—if $P$ is in kPa and $V$ in m $^3$ , use $R = 8.314$ J mol $^{-1}$ K $^{-1}$ .

References and further reading

Frequently Asked Questions

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Calculator info

Version:: v1.0.0
Last reviewed:: Nov 15, 2025
Sensitivity:: low
References:: 1

Last updated: November 19, 2025

Molar mass of gas calculator explained

Use it to confirm the identity of laboratory gases, check whether a sample is dry, or demonstrate how density and molar mass are connected.

How the conversion works

Starting from $PV = nRT$ :

n = \\frac{P V}{R T}, \\qquad M = \\frac{m}{n}

Units and conversions

Quantity	Units	Notes
Pressure $P$	atm, bar, kPa	Convert gauge readings to absolute pressure.
Volume $V$	L, m $^3$	Must match the pressure unit and chosen $R$ .
Temperature $T$	K	Convert deg C to K by adding 273.15.
Gas constant $R$	depends on units	e.g., 0.082057 L atm mol $^{-1}$ K $^{-1}$ .
Mass $m$	g	Same unit appears in molar mass output.
Molar mass $M$	g/mol	$M = m / n$ .

Worked examples

Identify an unknown cylinder gas
$m = 0.845\\ \\text{g}$ , $P = 0.978\\ \\text{atm}$ , $V = 0.250\\ \\text{L}$ , $T = 295\\ \\text{K}$ , $R = 0.082057$ .

n = \\frac{0.978 \\times 0.250}{0.082057 \\times 295} = 1.01 \\times 10^{-2}\\ \\text{mol}

M = \\frac{0.845}{1.01 \\times 10^{-2}} = 83.7\\ \\text{g}\\,\\text{mol}^{-1}

The value suggests the gas could be SO $_2$ (64 g/mol) with moisture or another heavier species present; check for leaks or impurities.

Confirm density during gas evolution
$m = 1.52\\ \\text{g}$ collected at $P = 1.05\\ \\text{atm}$ , $V = 0.500\\ \\text{L}$ , $T = 330\\ \\text{K}$ .

n = \\frac{1.05 \\times 0.500}{0.082057 \\times 330} = 1.94 \\times 10^{-2}\\ \\text{mol}

M = \\frac{1.52}{1.94 \\times 10^{-2}} = 78.4\\ \\text{g}\\,\\text{mol}^{-1}

This matches benzene vapor (78.1 g/mol), confirming the sample is dry.

Tips and pitfalls

Correct for water vapor pressure if the gas was collected over water; subtract $P_{\\text{H}_2\\text{O}}$ from total pressure before applying the formula.
Always use absolute temperature; forgetting to convert deg C to K is the most common error.
For high-pressure or low-temperature data, apply a compressibility factor ( $Z$ ) or a real-gas equation of state to improve accuracy.
Maintain unit consistency—if $P$ is in kPa and $V$ in m $^3$ , use $R = 8.314$ J mol $^{-1}$ K $^{-1}$ .

Quick Summary

Calculator Tool

How this is calculated

What these terms mean

Universal gas constant

Mass

Molar mass

Moles

Pressure

Temperature

Volume

When to use this calculator

Molar mass of gas calculator explained

How the conversion works

Units and conversions

Worked examples

Tips and pitfalls

References and further reading

Frequently Asked Questions

Related Calculators

Molarity

Reconstitution

Mole

Neutralization

Resuspension

Detention time

Was this calculator helpful?

Found an error?

Calculator info

Molar mass of gas calculator explained

How the conversion works

Units and conversions

Worked examples

Tips and pitfalls

References and further reading

Frequently Asked Questions

Related Calculators

Molarity

Reconstitution

Mole

Neutralization

Resuspension

Detention time

Was this calculator helpful?

Found an error?

Calculator info