STP stands for Standard Temperature and Pressure: 0°C (273.15 K) and 1 atm (101.325 kPa). At STP, one mole of any ideal gas occupies 22.4 liters.

Why is molar volume 22.4 L/mol?

Derived from the ideal gas law (PV = nRT): V/n = RT/P = (0.08206 L·atm/mol·K × 273.15 K) / 1 atm ≈ 22.4 L/mol at STP.

Is this accurate for real gases?

The 22.4 L/mol molar volume applies to ideal gases. Real gases deviate slightly, especially at high pressures or low temperatures, but it is accurate enough for most chemistry coursework.

How do I find the mass of a gas at STP?

First calculate moles = volume ÷ 22.4. Then multiply moles by the molar mass (g/mol) of the gas. This calculator handles that automatically when you enter the molar mass.

What is the new IUPAC STP?

IUPAC redefined STP in 1982 to 0°C and 100 kPa (not 101.325 kPa), giving a molar volume of 22.711 L/mol. This tool uses the traditional 22.4 L/mol (1 atm) still common in most textbooks.

Moles of Gas at STP Calculator

Name: Moles of Gas at STP Calculator
Availability: InStock
Author: Nham Vu

Calculate volume, moles, or mass of an ideal gas at STP (0°C, 1 atm) using the 22.4 L/mol molar volume.

What do you want to find?

STP: 0°C (273.15 K), 1 atm — molar volume = 22.4 L/mol

Number of moles (mol)

Result

Enter values and click Calculate

Common Gas Molar Masses (for reference)

Gas	Formula	Molar Mass (g/mol)

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