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Ideal Gas Law Calculator

Solve PV = nRT for pressure, volume, moles, or temperature. Supports atm, kPa, mmHg, psi, bar, L, mL, m^3, gal, and degC, K, degF inputs.

Ideal Gas Law Calculator (PV = nRT)

Given P, n, and T, find volume: V = nRT / P.

Absolute pressure, not gauge. Must be greater than zero.

Amount of gas in moles. Must be greater than zero.

Absolute temperature in Kelvin. Celsius and Fahrenheit are converted.

g/mol

Provide a molar mass to also compute gas density in g/L.

Volume (V) in L

22.41397

Pressure (P)

1 atm

Volume (V)

22.41397 L

Moles (n)

1 mol

Temperature (T)

273.15 K

SI: pressure

101,325 Pa

SI: temperature

273.15 K

At STP (273.15 K, 1 atm)

Ideal Gas Law Examples

PressureVolumeTemperatureAmount
1 atm22.414 L273.15 K1 mol
1 atm24.465 L298.15 K1 mol
2 atm12.233 L298.15 K1 mol
1 atm11.207 L273.15 K0.5 mol
1 atm49.751 L303.15 K2 mol

These ideal values use PV = nRT. Real gases can depart from this model.

Frequently Asked Questions about the Ideal Gas Law Calculator

What is the ideal gas law?
The ideal gas law is PV = nRT. Pressure (P) times volume (V) equals moles (n) times the gas constant (R) times absolute temperature (T). Real gases follow it closely at low pressure and moderate temperature.
Why does temperature have to be in Kelvin?
PV = nRT is built on absolute temperature, so T = 0 means no thermal energy. Celsius and Fahrenheit have arbitrary zero points and can be negative, which would make pressure or volume come out negative. This calculator accepts Celsius and Fahrenheit and converts to Kelvin internally.
Which value of R should I use?
R is the same constant, just in different units. In SI units, R = 8.314 J/(mol K). When pressure is in atm and volume in liters, R = 0.08206 L atm / (mol K). This calculator uses the SI value internally and converts every input to Pa, m^3, mol, and K.
What is STP and how does it differ from NTP?
This calculator labels 273.15 K and 1 atm as STP, the older convention that gives an ideal-gas molar volume of about 22.414 L. IUPAC's current standard pressure is 100 kPa, which gives about 22.71 L at 273.15 K. State the convention whenever you report an STP result.
How do I calculate gas density with the ideal gas law?
Gas density is mass per volume. From PV = nRT, density = PM/(RT), where M is molar mass. Enter molar mass in the optional field and the calculator reports density in g/L.

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