What is the ideal gas law?

The ideal gas law is PV = nRT, where P is the absolute pressure of the gas, V is the volume it occupies, n is the number of moles, R is the universal gas constant (8.314 J mol⁻¹ K⁻¹), and T is the absolute temperature in Kelvin. It combines Boyle's Law, Charles's Law, and Avogadro's Law into one equation.

What value of R does this calculator use?

R = 8.314 J mol⁻¹ K⁻¹ (equivalently 8.314 Pa·m³ mol⁻¹ K⁻¹). All inputs are converted to SI base units (Pa, m³, mol, K) before solving so that R stays constant.

Does temperature have to be in Kelvin?

The calculator accepts Celsius, Fahrenheit, or Kelvin. It automatically converts to Kelvin before applying PV = nRT because the ideal gas law requires an absolute temperature scale. A result in Kelvin can also be displayed in Celsius or Fahrenheit.

When is the ideal gas law a good approximation?

The ideal gas law works well for real gases at low to moderate pressures (below about 10 atm) and at temperatures well above the gas's boiling point. At very high pressures or near the boiling point, real-gas equations such as the van der Waals equation give more accurate results.

What if I get a negative or zero result?

A negative or zero result usually means one of the inputs is physically unreasonable — for example, a temperature entered as 0 K (absolute zero) or negative absolute temperature. Make sure temperatures are entered correctly and that all values are greater than zero.

Can I use this for mixtures of gases?

Yes, for ideal gas mixtures each component obeys PV = nRT independently (Dalton's Law of Partial Pressures). Enter the partial pressure of the component of interest along with its mole count to solve for that component's contribution.

Ideal Gas Calculator

Enter any three of P, V, n, and T and instantly solve for the missing variable using the ideal gas law PV = nRT.

Ideal Gas Law Inputs

Enter three known values and select which variable to solve for.

P × V = n × R × T

R = 8.314 J mol^-1 K^-1

Solve for

Pressure (P)

Volume (V)

Amount (n)

mol

Temperature (T)

Select a variable to solve for, fill in the other three, then click Calculate.

Solved Variable

All Values Summary

Variable	Description	Value

Step-by-Step Solution

Summary

The Ideal Gas Calculator solves the fundamental gas law PV = nRT, where P is pressure, V is volume, n is the amount of gas in moles, R is the universal gas constant, and T is absolute temperature. Enter any three of the four variables and the calculator instantly solves for the unknown. Unit conversions are handled automatically so you can mix pressure in atm, kPa, or mmHg with volume in liters or milliliters. All calculations run entirely in your browser with no data sent to any server.

How it works

Select which variable you want to solve for: Pressure (P), Volume (V), Moles (n), or Temperature (T).
Enter values for the other three variables in any supported unit.
Click Calculate — the tool applies PV = nRT with the universal gas constant R = 8.314 J/(mol·K).
The solved value is displayed along with a full summary table of all four variables.
A step-by-step solution shows the rearranged formula and substituted values.
Click Reset to clear all fields and start a new calculation.

Use cases

Calculate the pressure of a gas in a sealed container given its volume, moles, and temperature.
Determine how many moles of gas are present from measured pressure, volume, and temperature.
Find the temperature needed to achieve a target pressure at a known volume and mole count.
Solve chemistry homework and exam problems involving the ideal gas law.
Verify laboratory measurements by cross-checking PVT relationships.
Convert between pressure, volume, and temperature units while solving gas law equations.
Model gas behavior in engineering and thermodynamics applications.
Prepare for AP Chemistry, university general chemistry, or standardized science exams.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu