Calculation results
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Created by CalculatorOK Team · Last updated: Dec 21, 2025
Ideal Gas Law Calculator
What the Ideal Gas Law Calculator solves
Gases obey a surprisingly simple rule when pressures stay moderate and molecules stay far apart: PV = nRT. This calculator takes any three of Pressure, Volume, Temperature, and Moles, then solves for the missing fourth variable. Physics students, chemistry labs, HVAC technicians, and scuba fill stations all live inside this equation, since hydrogen, nitrogen, and air match it to within a fraction of a percent at room conditions.
A Pressure Unit selector converts results to atmospheres, kilopascals, bar, or other scales, so answers arrive in whichever convention your field prefers. That keeps homework answers and instrument readings in the same language.
The equation and a quick example
The law reads PV = nRT, with R equal to 8.314 J per mol K, temperature in kelvin, and pressure in pascals as long as the same unit system flows through every variable. Solve for whichever variable is missing by rearranging algebraically or, far easier, by letting the tool do it.
Try 2 moles of gas at 300 kelvin squeezed into 0.05 cubic meters. Solving for P gives nRT = 2 x 8.314 x 300 = 4988.4, divided by 0.05 for 99768 pascals, about 99.8 kilopascals. That lands within one percent of a standard atmosphere, a nice sanity check at ordinary conditions.
Using the calculator step by step
Enter any three known values with consistent units, set the Pressure Unit you want, and leave the unknown field for the tool to solve. Press Calculate and the missing variable appears. Convert Celsius to kelvin by adding 273.15 before typing Temperature, since the formula fails on negative scales.
Keep an eye on volume, because one liter is 0.001 cubic meters, an easy slip. When values drift far from room conditions, the ideal model ignores molecular size and attraction and loses accuracy. For dense or high-pressure gas, the van der Waals equation takes over instead.
Frequently Asked Questions
What is the gas constant R?
R equals 8.314 joules per mole per kelvin in SI units, tying energy, temperature, and amount of substance together. Use 8.314 when pressure is in pascals and volume in cubic meters.
How do I solve for pressure?
Enter Volume, Moles, and Temperature with consistent units, then leave Pressure blank and press Calculate. The tool computes P as nRT divided by V and converts it to your chosen Pressure Unit.
Does temperature need kelvin units?
Yes, always use absolute temperature in kelvin for PV = nRT. Add 273.15 to any Celsius reading first, because the equation breaks down when the scale can run negative.
Why does pressure rise with temperature?
Heating makes molecules move faster, so they strike the container walls harder and more often. With volume and moles fixed, doubling the kelvin temperature exactly doubles the pressure.
When does the ideal gas law fail?
It ignores molecular volume and attraction, so accuracy drops at high pressure or near the condensation point. For dense gases close to liquefaction, switch to the van der Waals equation instead.