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
| Field | What to enter |
|---|---|
| Find | Choose one: Pressure p, Volume V, Amount n, Temperature T |
| Pressure p | Units: kPa, Pa, bar, atm, psi, MPa |
| Volume V | Units: L, m³, mL, ft³ |
| Amount n (mol) | A number |
| Temperature T | Units: 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) |
|---|---|
| 50.66 | 101.3249 |
| 75.99 | 101.3249 |
| 101.33 | 101.3249 |
| 126.66 | 101.3249 |
| 151.99 | 101.3249 |
| 202.65 | 101.3249 |
Formula
p·V = n·R·T, R = 8.314462618 J/(mol·K)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.
Frequently asked questions
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).