What is the ideal gas law?

The ideal gas law states PV = nRT, relating pressure (P), volume (V), amount of gas in moles (n), the gas constant (R), and absolute temperature (T). It models how a hypothetical ideal gas behaves and is accurate for real gases at low pressure and high temperature.

What value of R does this calculator use?

It uses R = 0.0820573 L·atm·mol⁻¹·K⁻¹, which pairs with pressure in atmospheres, volume in litres, and temperature in kelvin. If you use SI units you need a matching value, such as 8.314 J·mol⁻¹·K⁻¹.

Why must temperature be in kelvin?

The ideal gas law requires absolute temperature, because at 0 K the gas would have zero pressure and volume. Convert from Celsius by adding 273.15. The temperature result also shows the Celsius equivalent.

How do I solve for pressure?

Rearrange PV = nRT to P = nRT / V. With n = 1 mol, T = 273.15 K and V = 22.414 L, P = (1 × 0.0820573 × 273.15) / 22.414 ≈ 1 atm — standard temperature and pressure.

What is the molar volume of a gas at STP?

One mole of an ideal gas occupies about 22.414 litres at standard temperature and pressure (273.15 K, 1 atm). Solving for V with n = 1, P = 1 and T = 273.15 returns this figure.

How do I convert the pressure result to kPa?

Multiply atmospheres by 101.325 to get kilopascals. The pressure output already shows both atm and kPa, so 1 atm is displayed as 101.325 kPa.

Does this work for real gases?

It treats the gas as ideal, which is a good approximation near room temperature and moderate pressure. Real gases deviate at very high pressure or near condensation, where equations like van der Waals are more accurate.

Is anything sent to a server?

No. Every calculation runs in your browser with plain JavaScript; no values are uploaded or stored.

Ideal Gas Law Calculator

Ideal gas law calculator

The ideal gas law, PV = nRT, links the pressure, volume, amount, and temperature of an ideal gas through the universal gas constant R. It is one of the cornerstone equations of chemistry and physics, used by students, lab technicians and engineers to predict how a gas responds when one variable changes. This calculator solves for any single unknown when you supply the other three values.

How it works

Pick which quantity is unknown, then enter the remaining three. The calculator rearranges PV = nRT to isolate your unknown:

Pressure: P = nRT / V
Volume: V = nRT / P
Amount of gas: n = PV / (RT)
Temperature: T = PV / (nR)

It uses R = 0.0820573 L·atm·mol⁻¹·K⁻¹, so pressure must be in atmospheres, volume in litres, amount in moles, and temperature in kelvin. Pressure results also display kilopascals (× 101.325) and temperature results display Celsius (− 273.15).

Example

Find the pressure of 1 mol of gas in a 22.414 L container at 273.15 K (standard temperature and pressure):

P = (n × R × T) / V = (1 × 0.0820573 × 273.15) / 22.414 ≈ 1 atm (101.325 kPa)

Quantity	Symbol	Unit	Example
Pressure	P	atm	1
Volume	V	L	22.414
Amount	n	mol	1
Temperature	T	K	273.15

Everything runs locally in your browser — no values are uploaded.