Chemistry Tools

Ideal Gas Law Calculator

Leave one field empty and the calculator solves for it. Pressure, volume and temperature each have their own unit menu, so you can enter kPa, mL and °C together without converting anything first.

Fill in every field except the one you want — the empty field is solved for. Mix any units you like.

V = 22.414 L

P
101.33 kPa
V
22.414 L
n
1 mol
T
273.15 K

Solved in SI units with R = 8.314 462 618 J·mol⁻¹·K⁻¹ (equivalently 0.082 057 L·atm·mol⁻¹·K⁻¹), then converted back to your chosen unit. Real gases deviate from ideal behaviour at high pressure and low temperature.

How it works

Every input is converted to SI — pascals, cubic metres, kelvin — and the equation is solved with the exact SI gas constant R = 8.314 462 618 J·mol⁻¹·K⁻¹. The answer is converted back into whichever unit you picked for it. The combined gas law mode solves P₁V₁/T₁ = P₂V₂/T₂ the same way, for a fixed amount of gas changing from one state to another.

Frequently asked questions

What is the ideal gas law?
PV = nRT: pressure × volume = moles × the gas constant × absolute temperature. It connects the four properties of a gas, so knowing any three gives the fourth.
Which value of R should I use?
It depends on your units: 0.082 057 L·atm/(mol·K), 8.314 J/(mol·K) = 8.314 L·kPa/(mol·K), or 62.364 L·mmHg/(mol·K). This calculator converts everything to SI internally, so you never need to choose.
Why must temperature be in kelvin?
Gas laws describe proportionality to absolute temperature. At 0 °C a gas still has plenty of volume, so doubling from 10 °C to 20 °C does not double anything — going from 283 K to 293 K is only a 3.5% increase.
What volume does one mole of gas occupy?
About 22.41 L at 0 °C and 1 atm, and about 22.71 L at IUPAC’s standard 0 °C and 100 kPa. At room temperature (25 °C, 1 atm) it is about 24.5 L.

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