The core idea
Use PV = nRT with consistent units: P in atm, V in liters, n in moles and T in kelvin when R = 0.082057 L·atm·mol⁻¹·K⁻¹. Gas behavior departs from ideality at high pressure and low temperature.
Try it yourself
Open the Ideal Gas Law Calculator and enter your own values. Keep units consistent and compare the answer with the worked explanation.
Check your work
Write down your known quantities, convert units before substitution and confirm that your final units match the quantity you intended to calculate.