🌡️ Charles's Law Calculator (V₁/T₁ = V₂/T₂)

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📘 About the Charles's Law

Charles's law says that at constant pressure, the volume of a fixed amount of gas is proportional to its absolute temperature. Heat a gas from 300 K to 600 K and its volume doubles.

Enter the temperatures in °C — the calculator converts them to kelvin, which the law needs. Using Celsius directly would give the wrong answer.

🧮 Formula

Charles's law
V₁ ÷ T₁ = V₂ ÷ T₂
Final volume
V₂ = V₁ × T₂ ÷ T₁

Where

  • V₁, V₂ = starting and final volume
  • T₁, T₂ = starting and final absolute temperature (K) = °C + 273.15
  • Pressure and amount of gas stay constant
Extending the V–T graph backwards to zero volume gives −273.15 °C, which is how absolute zero was first estimated.

✏️ Worked examples

Heating from 27 °C to 127 °C

You enter
Initial volume (V₁)2 L
Initial temperature (T₁)27 °C
Final temperature (T₂)127 °C
You get
Final volume V₂ (L)2.66633
Change in volume (L)0.666333
T₁ in kelvin300.15
T₂ in kelvin400.15

2 L of gas expands to 2.66633 L (300 K → 400 K).

Try this example →

Balloon in a freezer

You enter
Initial volume (V₁)3 L
Initial temperature (T₁)25 °C
Final temperature (T₂)-18 °C
You get
Final volume V₂ (L)2.56733
Change in volume (L)-0.432668
T₁ in kelvin298.15
T₂ in kelvin255.15

A 3 L balloon shrinks to 2.56733 L at −18 °C.

Try this example →

🧭 How to use this calculator

What you enter

  • Initial volume (V₁) (L)
  • Initial temperature (T₁) (°C)
  • Final temperature (T₂) (°C)

What you get

  • Final volume V₂ (L)
  • Change in volume (L)
  • T₁ in kelvin
  • T₂ in kelvin

💡 Charles's law in everyday life

  • Hot-air balloons rise because heated air expands and becomes less dense.
  • Tyres look flatter on cold mornings.
  • A dented table-tennis ball can be fixed in hot water.

❓ Frequently asked questions

What is Charles's law?

At constant pressure, the volume of a fixed amount of gas is directly proportional to its absolute temperature.

Why must temperature be in kelvin?

Volume is proportional to absolute temperature; 0 °C is not zero temperature, so ratios in °C are meaningless.

What is the formula of Charles's law?

V₁/T₁ = V₂/T₂.

What stays constant in Charles's law?

Pressure and the amount of gas.