Ideal Gas Law Calculator
Ideal Gas Law: PV = nRT
Enter any 3 values to calculate the 4th (R = 0.082057 L·atm/(mol·K))
Formula
PV = nRT
Where: P = Pressure, V = Volume, n = Moles, R = Gas constant, T = Temperature (Kelvin)
About This Calculator
Use the ideal gas law calculator when you want faster calculations with a clear method behind every result.
Solve for pressure, volume, temperature, or moles of gas using the ideal gas law (PV = nRT). Used in chemistry, thermodynamics, and engineering to model gas behavior under changing conditions.
If your workflow expands, pair this calculator with Heat Transfer Calculator and Carnot Efficiency Calculator to cross-check assumptions and build a stronger analysis chain.
Formula
PV = nRT, where P = pressure (Pa), V = volume (m³), n = moles, R = 8.314 J/(mol·K), T = temperature (K). Solve for any one variable given the other three.
Example Calculation
The worked example below demonstrates how the input fields translate into the final output. Use it as a quick validation pass before entering your own numbers.
- pressure (atm): 1
- moles (n): 1
- temperature (K): 273.15
Explanation of Results
Result Interpretation
At standard conditions (1 atm, 0°C = 273.15 K), 1 mole of ideal gas occupies 22.4 liters — the classic molar volume. V = nRT/P = 1 × 8.314 × 273.15 / 101325 = 0.02241 m³ = 22.41 L.
FAQ
What is the ideal gas law formula?
PV = nRT, where P is absolute pressure (pascals), V is volume (m³), n is the number of moles, R is the universal gas constant (8.314 J/mol·K), and T is absolute temperature in Kelvin. To convert Celsius to Kelvin: K = °C + 273.15.
When does the ideal gas law not apply?
The ideal gas law breaks down at high pressures (above ~10 atm) and low temperatures near condensation, where intermolecular forces become significant. Use the van der Waals equation for real gases in those conditions. At standard lab conditions (room temperature, 1 atm), ideal gas law gives < 1% error for most gases.
How do I use the ideal gas law to find moles?
Rearrange to n = PV / RT. Convert pressure to pascals (1 atm = 101,325 Pa), volume to m³ (1 L = 0.001 m³), and temperature to Kelvin. Example: a 5 L container at 2 atm and 25°C (298 K) holds n = (202650 × 0.005) / (8.314 × 298) = 0.409 moles.
How do I combine Boyle's Law and Charles's Law with this calculator?
The ideal gas law unifies both. For a fixed amount of gas (n constant), use P₁V₁/T₁ = P₂V₂/T₂ (the combined gas law). Set n = 1 and use the calculator twice — once for state 1 and once for state 2 — then compare results. Boyle's Law is the special case where T is constant; Charles's Law is where P is constant.
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See Also
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