Charles's Law Gas Temperature and Volume Calculator

Charles’s Law is one of the fundamental gas laws of physics and chemistry. Named after French physicist Jacques Charles (1746–1823), who formulated it in 1787, it describes the relationship between the volume and temperature of a gas at constant pressure.

The Law

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

V₁ / T₁ = V₂ / T₂

Where:

• V₁ = Initial volume
• T₁ = Initial temperature (in Kelvin)
• V₂ = Final volume
• T₂ = Final temperature (in Kelvin)

Critical: Always Use Kelvin

The formula only works with absolute temperature (Kelvin). To convert:

• Kelvin = Celsius + 273.15
• Kelvin = (Fahrenheit − 32) × 5/9 + 273.15

A temperature of 0°C = 273.15 K. Absolute zero (0 K = −273.15°C) is the point at which all molecular motion theoretically stops.

What the Law Means Physically

When you heat a gas at constant pressure, its molecules move faster and spread farther apart, so the gas expands. When you cool it, molecules slow down and the gas contracts. The relationship is linear: doubling the absolute temperature doubles the volume.

Real-World Examples

• Hot air balloon: Heating air inside the balloon increases its volume (and decreases density), creating lift. To ascend, the burner heats the air; to descend, the pilot releases hot air to let it cool.
• Car tires in summer: Tire pressure increases in hot weather because the gas inside expands.
• Bread rising in the oven: CO₂ bubbles inside the dough expand as temperature rises.
• Breathing: Diaphragm movement changes chest volume, causing air to flow in and out.

Limitations

Charles’s Law applies to ideal gases. Real gases deviate at very high pressures or very low temperatures, especially near the liquefaction point. For engineering applications with high-pressure or cryogenic gases, use more complete equations of state (van der Waals, etc.).