Ideal Gas Law Calculator (PV = nRT)
Pressure, volume, moles or temperature from PV = nRT, with atm, kPa, mmHg, bar and psi.
PV = nRT with R = 0.082057 L·atm/(mol·K). One mole at 0 °C (273.15 K) and 1 atm has V = 1 × 0.082057 × 273.15 ÷ 1 = 22.41 L.
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How to use it
- Choose the variable to solve for.
- Enter the other three with their units.
- Read the answer, converted into the unit you pick.
What you enter
- Three of pressure, volume, moles and temperature
What you get
- The fourth variable, with unit conversions
Formula
PV = nRT | R = 0.082057366 L·atm/(mol·K)
Worked example: pressure in a tank
Input: 2.0 mol in 10 L at 25 °C
Result: P = 4.89 atm (495.8 kPa)
Doubling the moles in the same tank doubles the pressure.
Questions
What value of R should I use?
Match R to your units: 0.08206 L·atm/(mol·K), 8.314 J/(mol·K) = 8.314 L·kPa/(mol·K), or 62.36 L·mmHg/(mol·K). This calculator converts units for you.
Why must temperature be in kelvin?
The law is proportional to absolute temperature, so 0 must mean no thermal energy. Add 273.15 to °C.
When does the ideal gas law fail?
At high pressure or low temperature, where molecular volume and attractions matter. Use the van der Waals equation there.
What is the molar volume of a gas at STP?
22.41 L at 0 °C and 1 atm, or 22.71 L at the IUPAC standard of 0 °C and 1 bar.
Limitations
- Real gases deviate at high pressure and near condensation.
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All free tools · By Dr. Zubair Khalid, DVM, MS, PhD.