About the Ideal Gas Law Calculator
The ideal gas law links four properties of a gas: its pressure, its volume, the amount of gas in moles and its temperature. Choose which one you want to find, enter the other three and the calculator solves PV = nRT. It uses kilopascals, litres and kelvin, and lets you type the temperature in Celsius if you prefer. Type the three values you know and the the ideal gas law appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Ideal Gas Law Calculator
- 1Enter the three values you know.
- 2Pick the units or options from the menus if the the ideal gas law tool offers them.
- 3Read the the ideal gas law in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the the ideal gas law
Chemistry students use the law to find the volume of gas made in a reaction or the number of moles in a flask. Engineers use it for tyres, compressed air and balloons, where a change in temperature changes the pressure.
Cooking and brewing fans use it to understand carbonation, divers to understand how air expands on the way up, and teachers to show Boyle's, Charles's and Gay-Lussac's laws as special cases.
How the the ideal gas law is worked out
P × V = n × R × T, where R is 8.314 J/(mol·K). With pressure in kPa and volume in litres, the product P × V is in joules. One mole of gas at 101.325 kPa and 273.15 K takes up 8.314 × 273.15 ÷ 101.325 = 22.41 litres. Going the other way, 22.4 litres at that pressure and temperature hold 0.9994 mol.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Solve for any of four variables
- Celsius or kelvin input
- Pressure also shown in atm and bar
Mistakes to avoid with the ideal gas law
Temperature must be absolute: a value in Celsius is converted to kelvin by adding 273.15, which the tool does for you. The law works best for gases at low pressure and high temperature. Near condensation, or at very high pressure, real gases deviate.
On phone and computer
On a phone, type into the boxes one after another and read the the ideal gas law underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the the ideal gas law move. The ideal gas law calculator works the same on both. Gas problems use other units and amounts. Convert pressure with Pressure Converter, temperature with Temperature Converter, concentration with Molarity Calculator, and find moles from mass with Molecular Weight Calculator.
Features
- Convert °C to K
- Use kPa and litres
- Real gases deviate at high pressure
- Clear messages when the the ideal gas law inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate the ideal gas law?
P × V = n × R × T, where R is 8.314 J/(mol·K). With pressure in kPa and volume in litres, the product P × V is in joules. One mole of gas at 101.325 kPa and 273.15 K takes up 8.314 × 273.15 ÷ 101.325 = 22.41 litres. Going the other way, 22.4 litres at that pressure and temperature hold 0.9994 mol.
What is the formula for the ideal gas law?
P × V = n × R × T, where R is 8.314 J/(mol·K). With pressure in kPa and volume in litres, the product P × V is in joules. The ideal gas law calculator applies it exactly and rounds only the displayed answer to six significant figures.
What is the gas constant R?
8.314462618 J/(mol·K). The tool uses it with kPa and litres so no conversions are needed.
What is standard temperature and pressure?
0 °C (273.15 K) and 100 kPa in the current IUPAC definition, or 101.325 kPa in older books. A mole then occupies about 22.7 litres at 100 kPa, or 22.4 litres at 101.325 kPa.
Can I use atmospheres or bar?
Convert first: 1 atm is 101.325 kPa and 1 bar is 100 kPa. The result for pressure is also given in atm and bar.
Is this ideal gas law calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.