# Charles's Law Calculator

Free Charles's Law calculator. Calculate gas volume or temperature at constant pressure using V1/T1 = V2/T2. Temperature must be in Kelvin.

## What this calculates

Calculate gas volume or temperature using Charles's Law: V₁/T₁ = V₂/T₂. This law states that at constant pressure, the volume of a gas is directly proportional to its absolute temperature (in Kelvin).

## Inputs

- **Solve For** — options: V₁ (Initial Volume), T₁ (Initial Temperature), V₂ (Final Volume), T₂ (Final Temperature) — Select which variable to calculate.
- **V₁ (Initial Volume)** (L) — min 0 — Initial volume of the gas in liters.
- **T₁ (Initial Temperature)** (K) — min 0 — Initial temperature in Kelvin. (K = °C + 273.15)
- **V₂ (Final Volume)** (L) — min 0 — Final volume of the gas in liters.
- **T₂ (Final Temperature)** (K) — min 0 — Final temperature in Kelvin. (K = °C + 273.15)

## Outputs

- **Result** — The calculated value.
- **Unit** — formatted as text — The unit of the result.
- **Formula** — formatted as text — Step-by-step calculation.

## Frequently Asked Questions

**Q: What is Charles's Law?**

A: Charles's Law states that for a fixed amount of gas at constant pressure, the volume is directly proportional to the absolute temperature. If you heat a gas, it expands; if you cool it, it contracts.

**Q: Why must temperature be in Kelvin?**

A: Charles's Law requires absolute temperature because the volume of an ideal gas is directly proportional to absolute temperature. Using Celsius or Fahrenheit would give incorrect results because they have arbitrary zero points. 0 K (absolute zero) is the true zero of temperature.

**Q: How do I convert Celsius to Kelvin?**

A: Add 273.15 to the Celsius temperature: K = °C + 273.15. For example, 25°C = 298.15 K, and 100°C = 373.15 K.

**Q: What happens at absolute zero?**

A: At absolute zero (0 K = -273.15°C), Charles's Law predicts zero volume. In reality, gases liquefy before reaching absolute zero, so the law no longer applies. Absolute zero is a theoretical limit that can never be reached.

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Source: https://vastcalc.com/calculators/chemistry/charles-law
Category: Chemistry
Last updated: 2026-04-21