Ideal Gas Law Calculator

An ideal gas is a theoretical gas where molecules have no volume and no intermolecular forces. Real gases approximate ideal behaviour at high temperatures and low pressures, where molecules are far apart and interactions are minimal. At extreme conditions, use the van der Waals equation instead.

The ideal gas law requires absolute temperature because volume and pressure are proportional to absolute temperature. At absolute zero (0 K = -273.15°C), all molecular motion ceases and gas volume approaches zero. Using Celsius would give negative absolute temperatures, which are physically meaningless in this context.

STP is defined as 0°C (273.15 K) and 100 kPa (approximately 1 atm). Under STP, 1 mole of any ideal gas occupies approximately 22.4 litres. This molar volume is a useful reference point for gas calculations.