How it’s calculated
An ideal gas obeys PV = nRT, where R is the molar gas constant. Real gases follow it closely at ordinary temperatures and pressures; it breaks down at high pressure or near the point where the gas condenses. Temperature must be absolute (kelvin), which this calculator handles for you.
Example (OpenStax Chemistry 2e §9.2, “Using the Ideal Gas Law”): 655 g of methane is 40.8 mol. At 25 °C (298.15 K) and 745 torr (0.980 atm), V = 40.8 × 0.08206 × 298.15 ÷ 0.980 ≈ 1,020 L.
At 0 °C and 1 atm one mole of any ideal gas occupies about 22.4 L.
Frequently asked questions
Why must temperature be in kelvin?
The law is a proportionality to absolute temperature. Using °C would make the volume zero at the freezing point of water, which is wrong. Add 273.15 to convert °C to K; the calculator does this for you.
Which value of R should I use?
Any, as long as the units match: 8.314 J/(mol·K) with Pa and m³, or 0.08206 L·atm/(mol·K) with atm and liters. The calculator converts everything to SI internally.
Should I use gauge or absolute pressure?
Absolute. A tire gauge reading of 32 psi is about 46.7 psi absolute at sea level (add 14.7 psi).
Embed this calculator
Add this free calculator to your own website. Copy the code below into your page’s HTML:
Sources
- Chemistry 2e, §9.2 Relating Pressure, Volume, Amount, and Temperature: The Ideal Gas Law — OpenStax
- CODATA value: molar gas constant — NIST
Formulas are taken from the free public references above. Results are provided “as is” for informational and educational purposes only. See our disclaimer.
Spotted a mistake or missing option? Report a problem · GitHub issue· Suggest a calculator