What is Charles's Law?

Charles's Law states that at constant pressure, the volume of a fixed amount of ideal gas is directly proportional to its absolute temperature (in Kelvin). Mathematically: V1 / T1 = V2 / T2, where the subscripts 1 and 2 refer to the initial and final states of the gas.

Why must temperature be in Kelvin?

Charles's Law uses absolute temperature because volume is proportional to absolute temperature, not to Celsius or Fahrenheit degrees. At 0 K (absolute zero), gas volume theoretically reaches zero. This calculator automatically converts Celsius and Fahrenheit inputs to Kelvin before solving.

What conditions must hold for this law to apply?

Charles's Law applies to ideal gases under two conditions: the pressure must remain constant (isobaric process) and the amount of gas must not change. Real gases approximate ideal behavior at low pressures and high temperatures.

Which units can I use for volume and temperature?

This calculator accepts volume in liters (L), milliliters (mL), and cubic centimeters (cm³), and temperature in Kelvin (K), Celsius (°C), and Fahrenheit (°F). All values are converted to common units before solving, so you can mix units freely.

What happens if I leave more than one field blank?

The calculator requires exactly three known values to solve for one unknown. If you leave two or more fields empty, it will show an error asking you to fill in the missing values.

Why does my result differ from a textbook answer?

Make sure your units match or that you are using the unit conversion options correctly. Also verify that the pressure and amount of gas are truly constant in your scenario — if either changes, you need the combined gas law or ideal gas law instead.

Charles's Law Calculator

Enter any three of V1, T1, V2, T2 and instantly solve for the missing variable using Charles's Law.

Enter Three Known Values

Leave exactly one field blank — that is the unknown to solve.

V₁ / T₁ = V₂ / T₂

Initial State

Initial Volume (V₁)

Initial Temperature (T₁)

Final State

Final Volume (V₂)

Final Temperature (T₂)

Fill in three values and click Calculate

Solved Variable

All Values Summary

Variable	Description	Value

Step-by-Step Solution

Summary

The Charles's Law Calculator applies the relationship V1/T1 = V2/T2, which describes how the volume of a fixed amount of gas at constant pressure is directly proportional to its absolute temperature. Enter any three of the four variables and the calculator instantly solves for the unknown. Temperature values are accepted in Celsius, Kelvin, or Fahrenheit and converted internally to Kelvin. All calculations run client-side with no data sent to any server.

How it works

Enter values for three of the four variables: Initial Volume (V1), Initial Temperature (T1), Final Volume (V2), or Final Temperature (T2).
Leave exactly one field blank — that is the unknown the calculator will solve.
Select the appropriate unit for each volume and temperature field.
Click Calculate to apply the formula V1 / T1 = V2 / T2.
The result appears instantly with the solved value highlighted and a step-by-step breakdown.
Click Reset to clear all fields and start a new calculation.

Use cases

Solve chemistry homework problems involving gas volume and temperature changes.
Predict the new volume of a balloon when it is moved from a warm room to the cold outdoors.
Calculate the temperature needed to expand a gas to a target volume in a lab setting.
Verify experimental results by cross-checking measured volume-temperature pairs.
Understand the direct relationship between volume and absolute temperature for ideal gases.
Prepare for AP Chemistry or university-level gas law exams.
Model thermal expansion of gases in engineering applications.
Convert between Celsius, Kelvin, and Fahrenheit while solving gas law problems.

Frequently Asked Questions

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