Solve Charles's law V₁/T₁ = V₂/T₂ for any missing volume or temperature at constant pressure. Enter temperatures in °C, °F or kelvin: they are converted to kelvin for you, and every step of the working is shown.
Last updated:
Solve for
Initial state (1)
Final state (2)
Enter your values to see the result.
Advertisement
Advertisement
How to use the Charles's Law Calculator
Choose the unknown: V₁, T₁, V₂ or T₂.
Pick the temperature and volume units you have.
Enter the three known values for the initial and final state.
Press Solve to get the answer with kelvin conversions and the rearranged formula.
Check the table and chart to see how the volume changes over a range of temperatures.
Charles's law formula
Unknown
Formula (T in K)
Example
Final volume V₂
V₂ = V₁ · T₂ ÷ T₁
3.00 L × 255.15 K ÷ 295.15 K = 2.59 L
Final temperature T₂
T₂ = T₁ · V₂ ÷ V₁
298.15 K × 500 mL ÷ 250 mL = 596.3 K
Initial volume V₁
V₁ = V₂ · T₁ ÷ T₂
600 mL × 300 K ÷ 450 K = 400 mL
Initial temperature T₁
T₁ = T₂ · V₁ ÷ V₂
450 K × 400 mL ÷ 600 mL = 300 K
Converting temperatures to kelvin
From
To kelvin
Example
Celsius
K = °C + 273.15
25 °C = 298.15 K
Fahrenheit
K = (°F − 32) × 5/9 + 273.15
72 °F = 295.37 K
Kelvin
no change
300 K
A handy rule of thumb: near room temperature, a gas at constant pressure changes volume by about 1/293 (0.34%) for every 1 °C change. Charles's law holds well for gases far from condensing; real gases depart from it near their boiling point and at high pressure. If pressure changes too, use the combined gas law calculator.
Frequently asked questions
What is Charles's law?
Charles's law states that at constant pressure, the volume of a fixed amount of gas is directly proportional to its absolute temperature: V₁/T₁ = V₂/T₂. Doubling the temperature in kelvin doubles the volume.
Why do I have to use kelvin in Charles's law?
Volume is proportional to absolute temperature, which starts at absolute zero. Celsius and Fahrenheit have arbitrary zero points, so using them directly gives wrong answers or a division by zero at 0 °C. Convert with K = °C + 273.15 or K = (°F − 32) × 5/9 + 273.15.
How do I find the final volume?
Use V₂ = V₁ × T₂ ÷ T₁ with temperatures in kelvin. A 3.00 L balloon at 22 °C (295.15 K) cooled to −18 °C (255.15 K) shrinks to 3.00 × 255.15 ÷ 295.15 ≈ 2.59 L.
How do I find the final temperature?
Use T₂ = T₁ × V₂ ÷ V₁. To double the volume of a gas at 25 °C (298.15 K), heat it to 596.3 K, which is 323.15 °C, not 50 °C.
What are everyday examples of Charles's law?
A balloon shrinks in the cold and expands in the sun, hot-air balloons rise because heated air expands and becomes less dense, bread rises in the oven, and a sealed bag of chips puffs up in a hot car.
How does Charles's law relate to absolute zero?
Extending the straight line of volume against temperature back to zero volume lands at about −273 °C. That observation helped define absolute zero, 0 K = −273.15 °C, the lowest possible temperature.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.