MihsabaShare this free calculator
Send this tool to someone who needs the calculation.
How to use
Use the ideal gas equation calculator to solve PV=nRT for pressure, volume, moles or absolute temperature. Enter any three known values and the calculator converts units to SI internally before solving the fourth. When solving PV=nRT, do not substitute Celsius directly for kelvin: 25°C is 298.15 K. One mole at 25°C and absolute pressure 2 atm occupies approximately 12.2327 L in the ideal model. R must match the pressure and volume units; this calculator uses R≈8.314462618 J/(mol·K) after SI conversion.
- Choose pressure, volume, moles or temperature as the unknown.
- Enter the three known values and units.
- Calculate; temperature is converted to kelvin, pressure to pascals and volume to m³ internally.
How it is calculated
Example
Example: at 1 atm, 1 mol and 273.15 K, V=nRT/P≈0.022414 m³≈22.414 L.
Important notes
P in PV=nRT is absolute pressure, not gauge pressure. The ideal model can deviate from real gases, especially at high pressure or near condensation. Do not substitute it for real-gas property or safety data.
Worked examples and interpreting results
One mole of an ideal gas at 273.15 K and one standard atmosphere occupies about 22.414 L. Raising temperature to 298.15 K at fixed pressure and amount increases the volume.
| Case | Calculation | Result |
|---|---|---|
| Volume at 273.15 K | 1 × 8.31446261815324 × 273.15 ÷ 101325 × 1000 | 22.41397 L |
| Volume at 298.15 K | 1 × 8.31446261815324 × 298.15 ÷ 101325 × 1000 | 24.465404 L |
| Volume: one mole, 25°C, absolute pressure 2 atm | 1 × 8.31446261815324 × 298.15 ÷ (2 × 101325) × 1000 | 12.232702 L |
| Moles: volume 10 L, 25°C, absolute pressure 1 atm | 101325 × (10 ÷ 1000) ÷ (8.31446261815324 × 298.15) | 0.40874 mol |
How to check the result
Use absolute pressure and absolute temperature, rather than gauge pressure or raw Celsius values. The ideal-gas assumption can become inaccurate at high pressure or near condensation even when the inputs are valid.
Ideal gas law calculator: PV = nRT
The ideal gas law relates pressure, volume, amount of gas and absolute temperature. For pressure in pascals use R = 8.314462618 J/(mol·K), volume in cubic metres and temperature in kelvins.
- 1 mol at 300 K in 0.025 m³: 1×8.314462618×300÷0.025 = ≈ 99,774 Pa
- 2 mol at 300 K in 0.05 m³: 2×8.314462618×300÷0.05 = ≈ 99,774 Pa
- Pressure ratio when absolute temperature doubles: 2P÷P = 2
Calculation caveat
Use absolute temperature in kelvins rather than Celsius and keep units consistent. Real gases may deviate strongly under high pressure or low temperature.
Related calculators
Frequently asked questions
What is the ideal gas equation?
PV=nRT, where P is absolute pressure, V is volume, n is amount in moles, R is the gas constant and T is absolute temperature.
Why must temperature be absolute?
PV=nRT requires an absolute temperature scale, so Celsius or Fahrenheit must first be converted to kelvin.
Can I use psi and cubic feet?
Yes. Selected units are converted to SI internally.
Is 1 atm equal to 101325 Pa?
Yes, that conversion is used here.
Is the ideal gas law exact for real gases?
No. It is a model; real-gas corrections may be needed at high pressure or near phase changes.
How do I calculate moles with PV=nRT?
Rearrange to n = PV/(RT). Use absolute pressure, kelvin temperature and units compatible with R. Select moles as the unknown in the calculator.