The ideal gas law PV = nRT links pressure, volume, amount and temperature of a gas. Pick the unknown, enter the other three in atm, litres, moles and kelvin, and the result follows from R = 0.082057 L·atm/(mol·K). One mole at 273.15 K and 1 atm, for example, occupies 22.414 L.
General chemistry problems keep returning to the same four quantities: how hard a gas pushes, how much space it takes, how many moles are present and how hot it is. This calculator rearranges PV = nRT for whichever one is missing, shows the substituted equation, and reports the pressure in kPa, the temperature in °C and the molar volume alongside the answer so you can sanity-check it against 22.4 L/mol. Inputs use the units most textbooks pair with R = 0.082057 L·atm/(mol·K): atmospheres, litres, moles and kelvin. The limit is the model itself: real gases at high pressure or near their condensation point stray from ideal behaviour, and the tool warns when your numbers drift into that region.
Select pressure, volume, moles or temperature under Solve for; its input box disappears.
Type pressure in atm, volume in litres, amount in moles and temperature in kelvin.
The answer, its unit, kPa and °C conversions and the substituted equation update as you type.
Result Result: 22.414
Unit of the result: L
Pressure in kPa: 101.325
Temperature in °C: 0
Molar volume (L/mol): 22.414
The classic molar volume: one mole of an ideal gas at 273.15 K and 1 atm fills about 22.414 L.
Result Result: 0.8124
Unit of the result: mol
Pressure in kPa: 202.65
Temperature in °C: 26.85
Molar volume (L/mol): 12.309
A 10 L vessel at 2 atm and 27 °C holds about 0.81 mol of gas, roughly 26 g of oxygen.
Result Result: 2.4465
Unit of the result: atm
Pressure in kPa: 247.896
Temperature in °C: 25
Molar volume (L/mol): 10
Half a mole squeezed into 5 L at room temperature exerts about 2.45 atm, or 247.9 kPa.
PV = nRT, so P = nRT/V, V = nRT/P, n = PV/(RT), T = PV/(nR)
PVnRTThe gas constant comes from the exact SI value 8.314462618 J/(mol·K) divided by 101.325 J per L·atm. The tool solves the rearranged equation directly, then converts pressure to kPa by multiplying by 101.325 and temperature to °C by subtracting 273.15. Molar volume is V divided by n, which equals 22.414 L/mol at 0 °C and 1 atm for any ideal gas.
It uses 0.082057366 L·atm/(mol·K), the exact SI gas constant 8.314462618 J/(mol·K) expressed in litre-atmospheres. That pairing matches the atm, L, mol and K inputs, so no conversion factor is needed.
The law depends on absolute temperature, which starts at zero where an ideal gas would have no volume. Celsius has its zero at the freezing point of water, so doubling a Celsius value does not double the volume. Add 273.15 to a Celsius reading before entering it.
Divide kPa by 101.325, or divide mmHg (torr) by 760. A 750 mmHg reading is 0.9868 atm, and 200 kPa is 1.974 atm.
It is volume divided by moles. At 0 °C and 1 atm every ideal gas gives 22.414 L/mol; at 25 °C and 1 atm it rises to about 24.47 L/mol. A value far from these at ordinary conditions points to an input unit slip.
Multiply moles by the molar mass. For 0.8124 mol of oxygen (32.00 g/mol) the mass is about 26.0 g; for the same amount of helium (4.003 g/mol) it is 3.25 g.
Deviations grow when molecules are pushed close together or move slowly: high pressure, low temperature, or gases with strong attractions such as ammonia and water vapour. At 1 atm and room temperature errors for nitrogen or oxygen are well below 1 %.
Using this tool in an assignment, article or report? Copy a citation, or a link for your website.
Tools Directory Editorial Team. (2026, October 27). Ideal Gas Law Chemistry. Tools Directory. Retrieved October 27, 2026, from https://tools.milunir.com/chemistry/gas-laws-and-thermodynamics/ideal-gas-law-chemistry/
Tools Directory Editorial Team. “Ideal Gas Law Chemistry.” Tools Directory, 27 Oct. 2026, https://tools.milunir.com/chemistry/gas-laws-and-thermodynamics/ideal-gas-law-chemistry/. Accessed 27 Oct. 2026.
Tools Directory Editorial Team. “Ideal Gas Law Chemistry.” Tools Directory. Last modified October 27, 2026. Accessed October 27, 2026. https://tools.milunir.com/chemistry/gas-laws-and-thermodynamics/ideal-gas-law-chemistry/.
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