# Ideal Gas Law Calculator

URL: https://speedycalculator.com/calculators/physics/ideal-gas-law/
Last updated: 2026-10-30

> The ideal gas law calculator solves pV = nRT for pressure, volume, amount of substance or temperature when the other three are known.

## Inputs

- Find
- Pressure p (kPa, Pa, bar, atm, psi, MPa)
- Volume V (L, m³, mL, ft³)
- Amount n (mol)
- Temperature T (K, °C, °F)

## Results

- Pressure p
- Volume V
- Amount n
- Temperature T
- Number of molecules

## Formula

```
p·V = n·R·T,  R = 8.314462618 J/(mol·K)
```

## Explanation

The ideal gas law ties together the four properties of a gas. It describes air, helium and most gases well at ordinary conditions – one of the most useful equations in physics and chemistry.

### How to use the Ideal Gas Law Calculator

- **Find**
- **Pressure p**
- **Volume V**
- **Amount n (mol)**
- **Temperature T**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Choose the unknown and enter the other three values.

### Tips

- Use absolute temperature (K) in gas laws and efficiency formulas.
- Temperature differences are the same in K and °C.
- Heat = mass × specific heat × temperature change when no phase change occurs.
- Phase changes need latent heat at a constant temperature.

### Common mistakes to avoid

- Using °C in pV = nRT.
- Forgetting latent heat during melting or boiling.
- Confusing heat capacity (J/K) with specific heat (J/(kg·K)).

### Inputs explained

FieldWhat to enterFindChoose one: Pressure p, Volume V, Amount n, Temperature TPressure pUnits: kPa, Pa, bar, atm, psi, MPaVolume VUnits: L, m³, mL, ft³Amount n (mol)A numberTemperature TUnits: K, °C, °F

### What each result means

- **Pressure p** = [Amount n (mol)]×8.314462618×[Temperature T]÷[Volume V]
- **Volume V** = [Amount n (mol)]×8.314462618×[Temperature T]÷[Pressure p]
- **Amount n** = [Pressure p]×[Volume V]÷(8.314462618×[Temperature T])
- **Temperature T** = [Pressure p]×[Volume V]÷([Amount n (mol)]×8.314462618)

### Example values

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

Pressure p (kPa)Pressure p (kPa)50.66101.324975.99101.3249101.33101.3249126.66101.3249151.99101.3249202.65101.3249

## Worked example

Inputs — Find: Pressure p; Volume V: 22.414 L; Amount n (mol): 1; Temperature T: 273.15 K.

Results — **Pressure p = 101.324862 kPa**; Number of molecules = 6.0221e23.

## Key terms

- **Ideal gas**: Point particles with no interactions.

## FAQ

**What is the value of R?**
8.314 J/(mol·K), or 0.08206 L·atm/(mol·K).

**What volume does 1 mol occupy?**
22.4 L at 0 °C and 1 atm.

**When does the ideal gas law fail?**
At high pressure or low temperature, near condensation.

**Do I need absolute temperature?**
Yes – kelvin.

**What formula does the Ideal Gas Law Calculator use?**
p·V = n·R·T,  R = 8.314462618 J/(mol·K).


## Sources

- [OpenStax – Chemistry 2e](https://openstax.org/details/books/chemistry-2e)
- [NIST – Fundamental physical constants](https://physics.nist.gov/cuu/Constants/)