Ideal Gas Law Calculator
Solve PV = nRT for any one variable. Useful for chemistry, engineering, and atmospheric science.
What is Ideal Gas Law Calculator?
The ideal gas law calculator applies PV = nRT, the fundamental relationship for gas behavior under typical conditions.
Formula
PV = nRT. P in atm, V in L, n in mol, T in K. R = 0.0821 L·atm/(mol·K).
Worked example
1 mol of gas at 273.15 K (0°C) and 1 atm: V = nRT/P = 1 × 0.0821 × 273.15 / 1 = 22.4 L. The molar volume at STP.
How to use this calculator
- Enter any three of P, V, n, T.
- Leave the fourth blank.
- The calculator solves for the missing value.
Frequently asked questions
What is R?
R is the universal gas constant. Value depends on units: 0.0821 L·atm/(mol·K) is most common; 8.314 J/(mol·K) for SI; 62.36 L·Torr/(mol·K) for mmHg pressure.
When does the ideal gas law fail?
At high pressures and low temperatures. Real gases deviate when molecules are forced close together (high P) or move slowly (low T). For typical conditions (1 atm, room temperature), it's very accurate.
Why use Kelvin?
Kelvin is an absolute temperature scale starting at 0 (no thermal motion). The gas law breaks if you use Celsius — temperatures become negative numbers, which is mathematically nonsensical for the law.
What is STP?
Standard Temperature and Pressure: 273.15 K (0°C) and 1 atm. At STP, 1 mole of any gas occupies 22.4 L. Useful reference point.