Ideal Gas Law Calculator

Select which variable to solve for, enter the remaining values, and calculate pressure, volume, moles, or temperature using the ideal gas law PV = nRT.

Created by Luis GonzalezLast updated: May 9, 2026

How to Use This Calculator

1
Enter Known Pressure
Input the gas pressure in atmospheres (atm). If solving for pressure, leave this blank.
2
Enter Known Volume
Input the gas volume in liters (L). If solving for volume, leave this blank.
3
Enter Moles of Gas
Input the amount of gas in moles (mol). If solving for moles, leave this blank.
4
Enter Known Temperature
Input the absolute temperature in Kelvin (K). Remember that 0°C equals 273.15 K. If solving for temperature, leave this blank.
5
Select Variable to Solve For
Choose which variable (Pressure, Volume, Moles, or Temperature) you wish the calculator to compute.
6
Review Solved Gas Property
Examine the calculated value for the unknown variable, along with conversions to other units and related gas properties.

Example Calculation

A chemist needs to determine the pressure of 1 mole of gas occupying 22.4 liters at 273.15 K, typical conditions at Standard Temperature and Pressure (STP).

Pressure

1 atm

Volume

22.4 L

Moles of Gas

1 mol

Temperature

273.15 K

Solve For

Pressure (P)

Results

1.00061 atm

Tips

Convert Temperature to Kelvin

Always convert temperature to Kelvin (K) for Ideal Gas Law calculations. Celsius or Fahrenheit will yield incorrect results, as Kelvin is an absolute temperature scale (0 K = absolute zero).

Understand the Gas Constant (R)

The ideal gas constant (R) is 0.08206 L·atm/(mol·K) when pressure is in atmospheres and volume in liters. Ensure your units match the R-value you use.

Check for Real Gas Deviations

The Ideal Gas Law works best for gases at low pressures and high temperatures. If your conditions are extreme (e.g., very high pressure, very low temperature), consider that real gases will deviate from ideal behavior.

Solving Gas Properties with the Ideal Gas Law Calculator

The Ideal Gas Law Calculator is an indispensable tool for students, chemists, and engineers, enabling the rapid calculation of pressure, volume, moles, or temperature of an ideal gas. Based on the fundamental equation PV = nRT, this calculator provides results in multiple units (atm, kPa, bar, psi) and offers insights into molar density and the nRT product. Understanding gas behavior is crucial in diverse fields, from predicting atmospheric pressure changes in meteorology to designing industrial chemical reactors, making this law a cornerstone of physical chemistry.

Real-World Applications of the Ideal Gas Law

The Ideal Gas Law is fundamental in various scientific and engineering fields. For example, in meteorology, it helps understand how atmospheric pressure changes with temperature and altitude, crucial for weather forecasting. In scuba diving, it's critical for calculating how compressed air in tanks behaves at different depths and temperatures, ensuring diver safety. Chemical engineers use it to design and optimize reactions involving gases, such as predicting product yields or reactor volumes. The standard molar volume of an ideal gas at STP (Standard Temperature and Pressure, 0°C and 1 atm) is approximately 22.4 L/mol, a key benchmark for many calculations.

The Ideal Gas Law Formula Explained

The Ideal Gas Law is expressed by the equation PV = nRT. This calculator allows you to solve for any one of these variables when the others are known.

Here's how each variable is calculated:

Pressure (P):
```
P = (n × R × T) / V
```
Volume (V):
```
V = (n × R × T) / P
```
Moles (n):
```
n = (P × V) / (R × T)
```
Temperature (T):
```
T = (P × V) / (n × R)
```

In these formulas, R is the ideal gas constant, typically 0.08206 L·atm/(mol·K). Ensure your units for pressure, volume, and temperature match those used for R.

💡 The Ideal Gas Law is a combination of simpler gas laws. To explore the relationship between volume and temperature at constant pressure, use our Charles's Law Calculator.

Calculating Pressure at Standard Temperature and Pressure

Let's use the Ideal Gas Law Calculator to find the pressure of 1 mole of gas under standard conditions:

Pressure: Leave blank (solving for P)
Volume: 22.4 L
Moles of Gas: 1 mol
Temperature: 273.15 K (which is 0°C)
Solve For: Pressure (P)

The calculator applies the formula P = (n × R × T) / V:

P = (1 mol × 0.08206 L·atm/(mol·K) × 273.15 K) / 22.4 L
P = 22.413759 L·atm / 22.4 L
P ≈ 1.00061 atm

The result shows that the pressure is approximately 1.00061 atm, confirming the expected value for an ideal gas at STP. The calculator also provides conversions to kPa (101.39 kPa), bar (1.0139 bar), and psi (14.71 psi), along with molar density and an nRT product verification.

💡 Beyond ideal gases, chemistry involves many fundamental calculations. For electrochemical reactions, our Cell Potential (EMF) Calculator can help determine reaction spontaneity.

Real-World Applications of the Ideal Gas Law

When the Ideal Gas Law Deviates: Real Gas Equations

The Ideal Gas Law (PV=nRT) serves as an excellent model for gases under ideal conditions—low pressures and high temperatures—where the assumptions of negligible molecular volume and intermolecular forces hold true. However, for real gases, especially at high pressures or low temperatures, these assumptions break down, and the ideal gas law becomes less accurate. In such scenarios, more complex equations of state, like the van der Waals equation, are employed: (P + a(n/V)²)(V - nb) = nRT. Here, the 'a' term corrects for the attractive forces between molecules, reducing the observed pressure, while the 'b' term accounts for the finite volume occupied by the gas molecules themselves. These real gas equations provide a more precise prediction of gas behavior in industrial processes, cryogenic applications, and advanced scientific research.

Frequently Asked Questions

What is the Ideal Gas Law?

The Ideal Gas Law is a fundamental equation in chemistry that describes the behavior of an ideal gas, a theoretical gas composed of randomly moving, non-interacting point particles. Expressed as PV = nRT, it relates the pressure (P), volume (V), number of moles (n), and absolute temperature (T) of a gas, with R being the ideal gas constant. It serves as a good approximation for many real gases under typical conditions.

What do the variables in PV=nRT represent?

In the Ideal Gas Law equation, PV=nRT: P stands for pressure (e.g., in atmospheres or Pascals), V for volume (e.g., in liters or cubic meters), n for the number of moles of gas, and T for absolute temperature (in Kelvin). R is the ideal gas constant, a proportionality constant that links the energy scales of temperature and pressure to the molar amount of gas, with a value of 0.08206 L·atm/(mol·K).

When is the Ideal Gas Law most accurate?

The Ideal Gas Law is most accurate for describing the behavior of real gases under conditions of low pressure and high temperature. Under these circumstances, the gas molecules are far apart and moving rapidly, minimizing the effects of intermolecular forces and the finite volume of the gas molecules themselves, thus closely mimicking the assumptions of an ideal gas. Deviations occur at high pressures or low temperatures.

What is Standard Temperature and Pressure (STP)?

Standard Temperature and Pressure (STP) is a set of standard conditions for experimental measurements, established to allow comparisons between different sets of data. The traditional STP values are 0°C (273.15 K) and 1 atmosphere (atm) of pressure. At STP, one mole of an ideal gas occupies approximately 22.4 liters, a value known as the standard molar volume.