What is the ideal gas law?

PV = nRT, where P is pressure, V volume, n the amount in moles, T absolute temperature and R = 8.314 J/(mol·K) the universal gas constant. It models a gas whose particles have negligible volume and no interactions.

Why must temperature be absolute?

The law uses kelvin because pressure and volume scale with absolute temperature. This tool converts Celsius or Fahrenheit to kelvin for you before computing.

What volume does one mole occupy?

At STP (1 atm, 273.15 K) one mole of an ideal gas occupies 22.414 L; at 1 bar and 273.15 K it is 22.711 L. Enter those values to verify.

When does the ideal gas law break down?

It is least accurate at high pressure and low temperature, where molecular volume and attractions matter. Real-gas equations like van der Waals correct for that.

Ideal Gas Law Calculator (PV = nRT)

The ideal gas law PV = nRT links the four state variables of a gas: pressure P, volume V, amount in moles n and absolute temperature T, tied together by the gas constant R = 8.314 J/(mol·K). Give this calculator any three and it solves for the fourth, converting every input to SI internally so you can mix units freely — pressure in Pa, kPa, bar, atm, mmHg (torr) or psi; volume in mL, L or m³; amount in mol or mmol; and temperature in kelvin, Celsius or Fahrenheit. For example, one mole at 1 atm and 273.15 K occupies 22.414 L, the molar volume at STP. The result comes back in whatever unit you selected for the unknown.

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Solve for

Pressure (P)

Volume (V)

Amount (n)

Temperature (T)

Result

22.41397 L

PV = nRT · R = 8.314 J/(mol·K)

PV = nRT with R = 8.314 J/(mol·K). Inputs are converted to SI (Pa, m³, mol, K) internally; temperature must be absolute.

How to use

Choose which variable to solve for: P, V, n or T.
Enter the other three with their units (temperature is converted to kelvin internally).
Read the result in the unit you picked for the unknown.

Frequently asked questions

What is the ideal gas law?: PV = nRT, where P is pressure, V volume, n the amount in moles, T absolute temperature and R = 8.314 J/(mol·K) the universal gas constant. It models a gas whose particles have negligible volume and no interactions.
Why must temperature be absolute?: The law uses kelvin because pressure and volume scale with absolute temperature. This tool converts Celsius or Fahrenheit to kelvin for you before computing.
What volume does one mole occupy?: At STP (1 atm, 273.15 K) one mole of an ideal gas occupies 22.414 L; at 1 bar and 273.15 K it is 22.711 L. Enter those values to verify.
When does the ideal gas law break down?: It is least accurate at high pressure and low temperature, where molecular volume and attractions matter. Real-gas equations like van der Waals correct for that.

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