# Gas Law Calculator

Solve pressure, volume, temperature, or moles with the Ideal Gas Law (PV=nRT) or Combined Gas Law; also gas density and molar mass.

> Canonical page: https://elysiatools.com/en/tools/gas-law-calculator

- **Category:** Math & Numbers

- **Keywords:** gas law, ideal gas, pv=nrt, combined gas law, thermodynamics, chemistry

## Overview

The Gas Law Calculator is a versatile thermodynamics tool designed to solve for unknown variables in gas behavior equations. It supports calculations using the Ideal Gas Law (PV=nRT), the Combined Gas Law (P1V1/T1 = P2V2/T2), and gas density or molar mass derivations, with flexible units for the gas constant (R) and temperature.

## Inputs

- **Calculation Mode** (select)
- **Gas Constant (R) Units** (select): Determines the pressure/volume units you must enter. Temperature is always converted to Kelvin internally.
- **Temperature Unit** (select)
- **Pressure (P)** (number): Leave blank to solve for pressure in Ideal mode.
- **Volume (V)** (number): Leave blank to solve for volume in Ideal mode.
- **Temperature (T)** (number): Leave blank to solve for temperature in Ideal mode.
- **Moles (n)** (number): Leave blank to solve for moles in Ideal mode.
- **Initial Pressure (P1)** (number): e.g. 1
- **Initial Volume (V1)** (number): e.g. 1
- **Initial Temperature (T1)** (number): e.g. 273.15
- **Final Pressure (P2)** (number): e.g. 2
- **Final Volume (V2)** (number): e.g. 0.5
- **Final Temperature (T2)** (number): e.g. 546.3
- **Molar Mass (g/mol)** (number): e.g. 28.97 for air
- **Mass of gas (g)** (number): e.g. 2
- **Decimal Places** (number)

## When to use

- When you need to find a single missing variable (pressure, volume, temperature, or moles) for an ideal gas under specific conditions.
- When analyzing a gas sample undergoing changes in pressure, volume, or temperature to determine its final state.
- When calculating the density or molar mass of a gas given its mass, temperature, and pressure.

## How it works

- Select the calculation mode: Ideal Gas Law, Combined Gas Law, or Density/Molar Mass.
- Choose your preferred Gas Constant (R) unit and Temperature unit (Kelvin or Celsius).
- Enter the known parameters, leaving the target variable blank if using the Ideal Gas Law mode.
- Click calculate to compute the missing value, rounded to your specified decimal places.

## Use cases

- Chemistry students verifying homework solutions for ideal gas volume or pressure calculations.
- Laboratory technicians determining the required volume of a gas cylinder at a specific pressure and temperature.
- Process engineers calculating gas density changes under varying thermal and pressure conditions.

## Frequently asked questions

### What gas constant (R) units are supported?

The calculator supports L·atm/mol·K, J/mol·K, m³·Pa/mol·K, L·kPa/mol·K, cal/mol·K, and cm³·mmHg/mol·K.

### Can I input temperatures in Celsius?

Yes, you can select Celsius or Kelvin; the tool automatically converts Celsius to Kelvin internally for calculations.

### How do I solve for a variable in the Ideal Gas Law mode?

Simply fill in the three known variables and leave the field for the unknown variable blank.

### What does the Combined Gas Law mode calculate?

It solves for any single unknown initial or final state variable (P1, V1, T1, P2, V2, T2) when a gas changes state.

### Can this tool calculate gas density?

Yes, by selecting the Density / Molar Mass mode and entering the mass, molar mass, pressure, and temperature.

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