Ideal Gas Law Calculator

Understanding the Ideal Gas Law

The ideal gas law PV = nRT describes the relationship between pressure (P), volume (V), amount of gas in moles (n), and temperature (T), where R is the universal gas constant (0.08206 L·atm/mol·K).

This calculator solves for any unknown variable when the other three are provided. It is widely used in chemistry, physics, and engineering for gas behavior calculations.

The Four Variables

• Pressure (P): Measured in atmospheres (atm). Standard atmospheric pressure is 1 atm, equivalent to 101.325 kPa or 760 mmHg.
• Volume (V): Measured in liters (L). Represents the space occupied by the gas.
• Moles (n): The amount of gas in moles. One mole contains 6.022 × 10²³ molecules (Avogadro's number).
• Temperature (T): Must be in Kelvin (K). Convert from Celsius by adding 273.15. The ideal gas law does not work with Celsius or Fahrenheit directly.

When Does the Ideal Gas Law Apply?

The ideal gas law assumes gas molecules have negligible volume and no intermolecular forces. It works well at high temperatures and low pressures, where real gases behave most like ideal gases. At very high pressures or very low temperatures, real gas behavior deviates significantly, and equations like the van der Waals equation provide better accuracy.

Common applications include calculating the volume of a gas at standard temperature and pressure (STP), determining the number of moles in a gas sample, and predicting how changes in temperature or pressure affect gas volume.

Related Gas Laws

The ideal gas law combines several earlier laws: Boyle's law (P ∝ 1/V at constant T and n), Charles's law (V ∝ T at constant P and n), and Avogadro's law (V ∝ n at constant P and T). Understanding these individual relationships helps build intuition for gas behavior problems.