Ideal Gas Calculator
Enter two of pressure/volume/temperature and the ideal gas law solves the third — with the Kelvin trap and unit conversions handled.
Last updated: 2026-09-28
How the calculation works
- Enter exactly two of p, V, T; the third solves algebraically with the gas constant R.
- Moles default to 1 so the reference point (22.4 L at STP) reproduces exactly.
- Outputs show every common pressure unit (kPa/atm/psi) to prevent unit slips.
Formula
p·V = n·R·T R = 8.314 J/mol·K
| Symbol | Meaning | Unit |
|---|---|---|
p | Absolute pressure | kPa |
V | Volume | L |
T | Absolute temperature | K |
n | Amount of gas | mol |
Worked example
Interpreting the result
The gas law is the backbone of pneumatics, HVAC air-side reasoning and tank physics: every 'what happens to pressure when…' question resolves from pV = nRT. Two habits prevent most errors: temperatures in Kelvin (always) and pressures in absolute (gauge + atmospheric). Real gases deviate near condensation — steam work needs steam tables, and high-pressure refrigerants need real-gas data; ambient air is where the ideal model shines.
Assumptions
- Ideal gas behavior — best for air and common gases near ambient conditions.
- Fixed amount of gas when solving the third property.
Limitations
- Not valid near condensation or at very high pressure (use real-gas EOS or steam tables).
- Does not cover mixtures' partial pressures explicitly (Dalton's law stacks separate calls).
Frequently asked questions
What is the ideal gas law?
pV = nRT: pressure × volume equals moles × gas constant × absolute temperature. It unites Boyle's, Charles's and Avogadro's relations into one equation.
Why must temperature be in Kelvin?
Because the law is proportional to absolute thermal energy — 0 °C is not zero energy. Using °C produces nonsense (negative pressures, wrong ratios). Always add 273.15.