What value of the gas constant R does this use?

It uses R = 0.0821 L-atm per mol-K. That means you should enter pressure in atmospheres, volume in liters, amount in moles, and temperature in kelvin for the units to be consistent.

Why must temperature be in kelvin?

The ideal gas law requires an absolute temperature scale, where zero means no thermal energy. Celsius or Fahrenheit can be negative and would give wrong results, so convert to kelvin by adding 273.15 to degrees Celsius.

What is an ideal gas?

An ideal gas is a simplified model whose particles have no volume and no attractive forces. Real gases follow PV = nRT closely at low pressure and high temperature but deviate under extreme conditions.

Can I solve for any of the four variables?

Yes. Select P, V, n, or T as the unknown, supply the other three values, and the calculator rearranges the equation accordingly. Solving requires the divisor not to be zero, for example volume when solving for pressure.

Ideal Gas Law Calculator

Volume (L)

Moles (mol)

Temperature (K)

Pressure (atm)1.0006

Volume (L)22.4000

Moles (mol)1.0000

Temperature (K)273.00

The ideal gas law, PV = nRT, links the pressure, volume, amount, and temperature of an ideal gas through the universal gas constant R. This calculator rearranges the equation to solve for whichever single variable you choose once the other three are known. It is a staple of chemistry and physics problems involving gases under everyday conditions.

Formula

P*V = n*R*T (R = 0.0821 L-atm/mol-K); e.g. P = nRT/V, V = nRT/P, n = PV/RT, T = PV/nR

P: Pressure in atmospheres (atm)
V: Volume in liters (L)
n: Amount of gas in moles (mol)
R: Universal gas constant, 0.0821 L-atm/(mol-K)
T: Absolute temperature in kelvin (K)

How it works

Choose which variable to solve for: pressure P, volume V, moles n, or temperature T.
Enter the three known values. Pressure is in atmospheres, volume in liters, amount in moles, and temperature in kelvin, matching the gas constant R = 0.0821 L-atm per mol-K used by the engine.
The calculator rearranges PV = nRT to isolate your chosen variable and returns its value, leaving the others as you entered them.

Worked examples

Find the pressure of 2 moles of gas in a 10 L container at 300 K.

Use P = nRT / V.
Compute the numerator: 2 x 0.0821 x 300 = 49.26.
Divide by the volume: 49.26 / 10 = 4.926.

The pressure is about 4.926 atm.

Find the volume of 1 mole of gas at 1 atm and 273.15 K (standard temperature).

Use V = nRT / P.
Compute the numerator: 1 x 0.0821 x 273.15 = 22.4256...
Divide by the pressure: 22.4256 / 1 = 22.4256.

The volume is about 22.426 L, close to the familiar molar volume of a gas near standard conditions.

Frequently asked questions

What value of the gas constant R does this use?: It uses R = 0.0821 L-atm per mol-K. That means you should enter pressure in atmospheres, volume in liters, amount in moles, and temperature in kelvin for the units to be consistent.
Why must temperature be in kelvin?: The ideal gas law requires an absolute temperature scale, where zero means no thermal energy. Celsius or Fahrenheit can be negative and would give wrong results, so convert to kelvin by adding 273.15 to degrees Celsius.
What is an ideal gas?: An ideal gas is a simplified model whose particles have no volume and no attractive forces. Real gases follow PV = nRT closely at low pressure and high temperature but deviate under extreme conditions.
Can I solve for any of the four variables?: Yes. Select P, V, n, or T as the unknown, supply the other three values, and the calculator rearranges the equation accordingly. Solving requires the divisor not to be zero, for example volume when solving for pressure.

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