Ideal Gas Law Formula Explained

This reference explains the Ideal Gas Law formula used by our free Ideal Gas Law Calculator. Use it to understand variables, units, and common mistakes before you calculate.

The formula

PV = nRT

Variables and units

• P — Pressure (atm, Pa, kPa)
• V — Volume (L, m³)
• n — Amount of gas (mol)
• R — Gas constant (0.08206 L·atm/(mol·K))
• T — Temperature (K (kelvin))

Worked example

Inputs: n = 2 mol, T = 300 K, V = 10 L — find pressure

1. P = nRT/V = (2 × 0.08206 × 300) / 10 = 4.92 atm

Result: Pressure ≈ 4.92 atm

When to use this formula

Use this formula when you need a quick ideal gas law estimate with values you already know. Our Ideal Gas Law Calculator applies the same relationship automatically so you can verify handwritten work.

Common mistakes

• Using Celsius instead of kelvin for temperature
• Mixing pressure units (atm vs Pa) with wrong R value
• Applying ideal gas law to high pressure or near liquefaction conditions

Frequently asked questions