# Combined Gas Law Calculator

URL: https://speedycalculator.com/calculators/physics/combined-gas-law/
Last updated: 2026-10-25

> The combined gas law calculator finds the new volume of a fixed amount of gas when pressure and temperature change, using P₁V₁/T₁ = P₂V₂/T₂. It covers Boyle’s, Charles’s and Gay-Lussac’s laws.

## Inputs

- Initial pressure (Pa, kPa, MPa, bar, atm, psi, mmHg)
- Initial volume (L, mL, m³)
- Initial temperature (K, °C, °F)
- Final pressure (Pa, kPa, MPa, bar, atm, psi, mmHg)
- Final temperature (K, °C, °F)

## Results

- Final volume

## Formula

```
V₂ = V₁ × (P₁ ÷ P₂) × (T₂ ÷ T₁)
```

## Explanation

Gases expand when heated and compress under pressure. The combined law handles both effects at once.

### How to use the Combined Gas Law Calculator

- **Initial pressure**
- **Initial volume**
- **Initial temperature**
- **Final pressure**
- **Final temperature**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Temperatures are converted to kelvin, then the starting volume is scaled by the pressure and temperature ratios.

### Inputs explained

FieldWhat to enterInitial pressureUnits: Pa, kPa, MPa, bar, atm, psi …Initial volumeUnits: L, mL, m³Initial temperatureUnits: K, °C, °FFinal pressureUnits: Pa, kPa, MPa, bar, atm, psi …Final temperatureUnits: K, °C, °F

### Example values

How the main result changes when **Initial pressure** changes and everything else stays at the example values above:

Initial pressure (Pa)Final volume (L)50,662.50.636475,993.750.9547101,3251.2729126,656.251.5911151,987.51.9093202,6502.5458

## Worked example

Inputs — Initial pressure: 101,325 Pa; Initial volume: 2 L; Initial temperature: 293.15 K; Final pressure: 202,650 Pa; Final temperature: 373.15 K.

Results — **Final volume = 1.2729 L**.

## FAQ

**When does this law apply?**
For a fixed amount of ideal gas.

**What if only temperature changes?**
Set P₂ equal to P₁ and it becomes Charles’s law.

**What formula does the Combined Gas Law Calculator use?**
V₂ = V₁ × (P₁ ÷ P₂) × (T₂ ÷ T₁).