Math
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)
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?
STP (standard temperature and pressure) is 273.15 K (0 C) and 1 atm. NTP (normal temperature and pressure) is 293.15 K (20 C) and 1 atm. At STP, one mole of an ideal gas occupies 22.414 liters.
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.