Power Calculators

🎈 Ideal Gas Law Calculator (PV = nRT)

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Enter details

Pick what you want to find. The box for that quantity is ignored, so you can leave any number in it.
1 atm = 101.325 kPa = 760 mmHg.
Enter in °C; it is converted to kelvin.

Fill in the details and click Calculate to see your results.

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📘 About the Ideal Gas Law

The ideal gas law, PV = nRT, connects the pressure, volume, amount and temperature of a gas. Choose which one you want to find, enter the other three, and this calculator solves the equation.

Enter pressure in atmospheres, volume in litres and temperature in degrees Celsius (it is converted to kelvin for you). Real gases follow the law closely at low pressure and high temperature.

🧮 Formula

Ideal gas equation
PV = nRT
Solved for each variable
P = nRT/V, V = nRT/P, n = PV/RT, T = PV/nR

Where

  • P = pressure (atm)
  • V = volume (L)
  • n = amount of gas (mol)
  • R = 0.082057 L·atm/(mol·K) = 8.314 J/(mol·K)
  • T = absolute temperature (K) = °C + 273.15
Always use kelvin in gas law calculations. Using °C directly gives wrong answers.

✏️ Worked examples

Volume of 1 mol at 0 °C and 1 atm

You enter
FindVolume (V)
Pressure (P)1 atm
Amount of gas (n)1 mol
Temperature (T)0 °C
You get
Pressure (atm)1
Pressure (kPa)101.325
Volume (L)22.414
Amount (mol)1
Temperature (K)273.15
Temperature (°C)0

One mole of an ideal gas occupies 22.414 L at 0 °C and 1 atm.

Try this example →

Pressure in a gas cylinder

You enter
FindPressure (P)
Volume (V)10 L
Amount of gas (n)20 mol
Temperature (T)25 °C
You get
Pressure (atm)48.9308
Pressure (kPa)4,957.91
Volume (L)10
Amount (mol)20
Temperature (K)298.15
Temperature (°C)25

20 mol of gas in a 10 L cylinder at 25 °C is at 48.9308 atm.

Try this example →

🧭 How to use this calculator

What you enter

  • FindPick what you want to find. The box for that quantity is ignored, so you can leave any number in it.
  • Pressure (P) (atm)1 atm = 101.325 kPa = 760 mmHg.
  • Volume (V) (L)
  • Amount of gas (n) (mol)
  • Temperature (T) (°C)Enter in °C; it is converted to kelvin.

What you get

  • Pressure (atm)
  • Pressure (kPa)
  • Volume (L)
  • Amount (mol)
  • Temperature (K)
  • Temperature (°C)

💡 Values of R in different units

  • 0.082057 L·atm/(mol·K)
  • 8.314 J/(mol·K) = 8.314 Pa·m³/(mol·K)
  • 0.08314 L·bar/(mol·K)
  • 62.36 L·mmHg/(mol·K)
  • 1.987 cal/(mol·K)

❓ Frequently asked questions

What is the ideal gas law?

PV = nRT, the equation of state of an ideal gas.

What is the value of R?

0.0821 L·atm/(mol·K), or 8.314 J/(mol·K).

Why must temperature be in kelvin?

Gas volume and pressure are proportional to absolute temperature; on the Celsius scale zero isn't the true zero.

When does a real gas behave like an ideal gas?

At low pressure and high temperature, when molecules are far apart and attract each other very little.