Standard Temperature and Pressure. IUPAC redefined it in 1982/2010 as 0 °C (273.15 K) and 100 kPa. Older texts used 101.325 kPa (1 atm), giving V_m = 22.414 L/mol. This calculator uses the current IUPAC definition.

Is this formula exact?

Only for ideal gases. Real gases deviate, especially at high pressures or near their boiling points. For most gases at STP the deviation is < 0.1%.

Gas Density at STP Calculator

Calculate the density of an ideal gas at STP (0 °C, 100 kPa, IUPAC 2010) and at SATP (25 °C, 100 kPa) from its molar mass. For education only.

By AbraCalc Editorial Team · Reviewed by AbraCalc Methodology Review · Last reviewed: 2026-06-25

Embed this tool on your site

<iframe src="https://abracalc.com/calculator/gas-density-stp-calculator/embed.html" width="340" height="320" style="border:1px solid #e4e7ec;border-radius:12px" loading="lazy"></iframe>

How to use this tool

Enter molar mass in the fields above.
Results update instantly as you type — or click Calculate.
Read your density at stp (0 °c, 100 kpa) and the full breakdown beneath it.

For an ideal gas: density = M / V_m, where M is molar mass (g/mol) and V_m is molar volume (L/mol). At STP (IUPAC 2010: 0 °C, 100 kPa) V_m = 22.711 L/mol. At SATP (25 °C, 100 kPa) V_m = 24.790 L/mol.

For education only.

Formula

Molar volume at STP (0 °C, 100 kPa): V_m = RT ÷ P = 8.314472 × 273.15 ÷ 100000 m³/mol ≈ 22.711 L/mol

Density at STP (g/L) = Molar mass (g/mol) ÷ V_m (L/mol)

Molar volume at SATP (25 °C, 100 kPa) = 8.314472 × 298.15 ÷ 100000 × 1000 ≈ 24.789 L/mol

How it works

Using the ideal gas law (PV = nRT), the molar volume of any ideal gas depends only on temperature and pressure, not its identity. At IUPAC 2010 STP (0 °C, 100 kPa) the molar volume is approximately 22.711 L/mol; dividing the gas's molar mass by this value gives its density in g/L. The calculator also provides values at SATP (25 °C, 100 kPa), the standard ambient temperature and pressure used in thermodynamics. Results are accurate for ideal gases; real gases deviate slightly, especially at high pressures or low temperatures.

Worked example

Worked example — carbon dioxide (CO₂)

Molar mass of CO₂ = 44.009 g/mol.
Molar volume at STP: V_m = 8.314472 × 273.15 ÷ 100000 × 1000 = 22.711 L/mol.
Density at STP = 44.009 g/mol ÷ 22.711 L/mol = 1.9379 g/L.

CO₂ density at STP = 1.9379 g/L; molar volume at STP = 22.711 L/mol.

Key terms

STP (Standard Temperature and Pressure): IUPAC 2010 definition: 0 °C (273.15 K) and 100 kPa. The older definition used 101.325 kPa.
SATP (Standard Ambient Temperature and Pressure): 25 °C (298.15 K) and 100 kPa; commonly used in thermodynamic tables.
Molar volume (V_m): The volume occupied by one mole of an ideal gas at a given temperature and pressure.
Ideal gas law: PV = nRT; relates pressure, volume, amount, and temperature of an ideal gas.
Molar mass: The mass of one mole of a substance in grams per mole (g/mol), numerically equal to its relative molecular mass.

Frequently asked questions

What is STP?: Standard Temperature and Pressure. IUPAC redefined it in 1982/2010 as 0 °C (273.15 K) and 100 kPa. Older texts used 101.325 kPa (1 atm), giving V_m = 22.414 L/mol. This calculator uses the current IUPAC definition.
Is this formula exact?: Only for ideal gases. Real gases deviate, especially at high pressures or near their boiling points. For most gases at STP the deviation is < 0.1%.