Ideal Gas Law Calculator

The ideal gas law is PV = nRT, where P is pressure (atm), V is volume (L), n is the amount of gas (mol), R is the ideal gas constant (0.0821 L·atm/(mol·K)), and T is absolute temperature (K). It combines Boyle's Law, Charles's Law, and Avogadro's Law into a single equation relating all four variables.

R is the ideal gas constant. Its value depends on the units used: R = 0.0821 L·atm/(mol·K) when pressure is in atmospheres and volume is in litres, or R = 8.314 J/(mol·K) when using SI units (pascals and cubic metres). This calculator uses the atm/L/mol/K form, the most common convention in introductory chemistry.

Add 273.15 to the Celsius temperature: K = °C + 273.15. The ideal gas law requires absolute temperature because it is derived from the kinetic theory of gases, where temperature must start at absolute zero. Using Celsius directly gives incorrect (and sometimes negative or infinite) results.

STP is defined as 0°C (273.15 K) and 1 atm of pressure. At STP, one mole of any ideal gas occupies 22.4 L, a value known as the standard molar volume. This calculator's default values (n=1, T=273.15 K, P=1 atm) reproduce this exact result, V = 22.43 L, as a built-in sanity check.

Yes, as an approximation. Real gases deviate from ideal behaviour at high pressure and low temperature, where intermolecular forces and molecular volume become significant. For most everyday chemistry problems at moderate conditions, the ideal gas law is accurate within a few percent. For more precise work on real gases, a compressibility factor (Z) correction is applied.

Rearrange PV = nRT to solve for T: T = PV / (nR). Enter the known pressure, volume, and moles, and select Solve T. For example, with P = 1.5 atm, V = 20 L, and n = 1.2 mol: T = (1.5 × 20) / (1.2 × 0.0821) = 304.51 K, which is 31.36°C.

According to Boyle's Law (a special case of PV = nRT), volume is inversely proportional to pressure when n and T are constant. If pressure doubles, volume is halved. You can verify this directly with the calculator: hold n and T fixed, double P in Solve V mode, and confirm the resulting V is exactly half.

Boyle's Law (PV = constant at fixed T and n) and Charles's Law (V/T = constant at fixed P and n) are both special cases of the ideal gas law PV = nRT. The ideal gas law is the general equation; Boyle's and Charles's Laws describe what happens when you hold two of the four variables constant and vary the other two.

Yes, if n represents the total moles of all gases combined, PV = nRT still holds for the total pressure (Dalton's Law of Partial Pressures). Each gas in the mixture also independently satisfies the ideal gas law using its own partial pressure and mole count.

Pressure is in atmospheres (atm), volume is in litres (L), amount of gas is in moles (mol), and temperature is in kelvin (K). These are the standard units that pair correctly with R = 0.0821 L·atm/(mol·K). If your data is in other units (kPa, mL, °C), convert before entering values.

The ideal gas law treats gas particles as point masses with no volume of their own, occupying only empty space between collisions. This assumption breaks down at high pressure, where molecules are packed closely enough that their actual volume becomes a meaningful fraction of the container volume, causing real gases to deviate from ideal predictions.

Yes, indirectly. First solve for moles (n) using PV = nRT with a measured mass sample's pressure, volume and temperature. Then divide the known mass of the sample by n to get molar mass (g/mol). This technique is commonly used in the lab to identify unknown gases from their measured PVT behaviour.