The ideal gas law ties together the four things you can measure about a gas: its pressure, volume, amount and temperature. Know three and this calculator finds the fourth, in whatever units your problem uses, converting to kelvin and matching the gas constant for you.
How to Use It
- Choose what to Find: Pressure, Volume, Moles or Temperature.
- Enter the other three values and pick each one’s unit.
- Choose the unit for the answer in Answer In.
- Press Calculate.
How It Works
R is the gas constant, 8.314 J/(mol·K). The calculator converts pressure to pascals, volume to cubic meters and temperature to kelvin, solves the equation for the unknown, then converts the answer to the unit you chose:
Worked Example
What volume does 1 mol of gas fill at 0 °C (273.15 K) and 1 atm (101,325 Pa)?
That’s the standard molar volume chemistry classes use for gases at STP.
Tips and Common Mistakes
- Always use kelvin. 25 °C is 298.15 K; plugging in 25 gives an answer over ten times too small.
- Match R to your units when working by hand: 0.08206 L·atm/(mol·K) or 8.314 J/(mol·K).
- Moles, not grams. Divide a mass by the molar mass first.
- Watch which STP. 0 °C and 1 atm gives 22.4 L per mole; IUPAC’s 1 bar gives about 22.7 L.
- Real gases differ at high pressure or low temperature, where molecules crowd and attract.