Ideal Gas Law Calculator
Solve PV = nRT for pressure, volume, amount of gas or temperature from the other three, in the units you have, with the molar volume.
Result
Volume: 24.4654 L
Exact for an ideal gas. Real gases deviate, most at high pressure and low temperature.
- Pressure
- 1 atm (14.6959 psi, 101.325 kPa)
- Amount of gas, mol
- 1
- Temperature
- 77 °F (25 °C, 298.15 K)
- Molar volume, L/mol
- 24.4654
https://calcgallery.com/chemistry/ideal-gas-law-calculator/
Results come from the published equations applied to the values you enter. They are not electrical design, conductor sizing, laboratory safety or medical guidance. Weather indices describe a standard person in standard conditions and are not a forecast. Where codes apply, local rules vary and must be checked. Read the full disclaimer
How to use the Ideal Gas Law Calculator
- Choose the quantity you want. The field for it disappears and the other three stay.
- Enter the three you know, each in whatever unit you have it in. Use absolute pressure and any temperature scale; the page converts to kelvin itself.
- Read the answer and the molar volume, the space one mole of the gas takes up under those conditions.
The formula
PV = nRTV = nRT ÷ P P = nRT ÷ V n = PV ÷ RT T = PV ÷ nRR = 8.314 462 618… J/(mol·K) = N_A × kmolar volume = V ÷ nP is absolute pressure, V the volume of the container, n the amount of gas in moles and T the absolute temperature.
Moles from a mass
If you know the mass of gas rather than the moles, divide the mass by the molar mass: 655 g of methane, CH₄ at 16.043 g/mol, is 40.83 mol. The grams to moles calculator does that step from a chemical formula.
What the diagram shows
A cylinder of gas under a piston, with the four quantities beside it and the one you solved for highlighted. The piston rises as the volume per mole grows, and more particles are drawn for more gas.
With your numbers
- In SI units: P = 101,325 Pa, V = 24.4654 L, n = 1 mol, T = 298.15 K
- V = nRT ÷ P = 1 × 8.314462618 × 298.15 ÷ 101,325 = 24.4654 L
Quick reference
Exact for an ideal gas. Real gases deviate, most at high pressure and low temperature.
| Example | Result |
|---|---|
| 1 mol at 0 °C and 1 atm | Volume: 22.414 L |
| 1 mol at 25 °C and 1 atm | Volume: 24.4654 L |
| Pressure of 2 mol in 10 L at 300 K | Pressure: 498.8678 kPa |
| Moles in 1 L at 100 kPa and 25 °C | Amount of gas, mol: 0.04034 |
| Temperature of 1 mol in 24.5 L at 1 atm | Temperature: 25.42 °C |
| Moles in 1 L at 1 atm and 77 °F | Amount of gas, mol: 0.040874 |
Where the numbers come from
The fixed figures this calculator relies on, and the published source each one was checked against. How the calculators are built and checked
1 source
BIPM, SI defining constants, SI Brochure (2019): N_A = 6.022 140 76 x 10^23 mol-1 and k = 1.380 649 x 10^-23 J K-1, both exact; NIST CODATA 2022, https://physics.nist.gov/cgi-bin/cuu/Value?r: "8.314 462 618... J mol-1 K-1 (exact)".
Used for
- The molar gas constant R = N_A k, exact since the 2019 SI: 8.314 462 618… J/(mol·K).
Common questions about the Ideal Gas Law Calculator
- What value of R does the page use?
- R = 8.314 462 618… J/(mol·K), the product of the Avogadro and Boltzmann constants, both fixed exactly by the 2019 redefinition of the SI. Textbooks quote it as 0.08206 L·atm/(mol·K) or 8.314 kPa·L/(mol·K); those are the same constant in other units, rounded. The page converts every input to pascals, cubic metres and kelvin, so no unit-matched R is needed.
- Why must the temperature be absolute?
- The law says volume is proportional to temperature, which is only true on a scale that starts at absolute zero. Doubling 10 °C to 20 °C does not double the volume; going from 283.15 K to 566.3 K would. Enter °C or °F if you like: the page converts to kelvin before calculating.
- What about gauge pressure?
- A tyre gauge or a gas-cylinder gauge reads pressure above the surrounding air. PV = nRT needs the absolute pressure, so add atmospheric pressure, about 101.3 kPa or 14.7 psi at sea level, to a gauge reading before entering it.
- Is 22.4 L per mole always right?
- Only at 0 °C and 1 atm, where one mole of an ideal gas takes 22.414 L. At 25 °C and 1 atm it is 24.465 L, and it changes with every condition, which is why the page prints the molar volume for yours.
- When does the ideal gas law fail?
- At high pressure, where the molecules’ own volume matters, and at low temperature near condensation, where they attract each other. This page makes no correction for real-gas behaviour, so treat answers under those conditions as a first estimate.