Ideal Gas Law Calculator
Use PV = nRT to calculate pressure, volume, moles, or temperature when you know the other three.
Result
Pressure
1.223 atm
123,900 Pa = 123.9 kPa = 1.223 atm
PV = nRT uses absolute pressure. Convert gauge pressure to absolute pressure before calculating.
The ideal gas law is an approximation. Real gases can deviate more noticeably at high pressure or low temperature.
Calculation working
How it was calculated
P = nRT ÷ V
V = 2.00 L = 0.002 m³
n = 0.100 mol
T = 25 °C = 298.1 K
P = (0.1 mol × 8.314 × 298.1 K) ÷ 0.002 m³
= 123,900 Pa = 123.9 kPa = 1.223 atm
What is the ideal gas law?
The ideal gas law describes the relationship between a gas's pressure, volume, amount, and temperature.
PV = nRT
- P —
- pressure
- V —
- volume
- n —
- amount of gas in moles
- R —
- gas constant — this calculator handles the unit conversions automatically
- T —
- absolute temperature in kelvin
How it works
Four short steps
Identify the three values you know
Pressure, volume, moles, or temperature — whichever three you have.
Choose the value you want to find
Pick the missing fourth value above.
Enter the values and units
Mixed units are fine; everything converts automatically.
Calculate the missing value
The answer appears immediately with the working shown.
Ideal gas law formulas
One relationship, rearranged four ways. You never need to rearrange it yourself — pick the unknown and the calculator applies the right form.
P = nRT ÷ V
V = nRT ÷ P
n = PV ÷ RT
T = PV ÷ nR
Worked example
2.00 L · 0.100 mol · 25 °C
V = 2.00 L = 0.002 m³
n = 0.100 mol
T = 25 °C = 298.1 K
P = (0.1 mol × 8.314 × 298.1 K) ÷ 0.002 m³
= 123,900 Pa = 123.9 kPa = 1.223 atm
Scope
When does the ideal gas law work best?
The ideal gas law is generally more useful when gas pressure is relatively low and temperature is relatively high.
Real-gas effects become more important at high pressure and low temperature, where the approximation can drift from measured values.
Keep going
Related tools
Find the moles or molar mass first, or use the result in a reaction calculation:
FAQ
Frequently asked questions
What is the ideal gas law?
The ideal gas law describes how a gas's pressure, volume, amount, and temperature relate: PV = nRT. It treats the gas as ideal particles with no interactions.
What does PV = nRT mean?
P is pressure, V is volume, n is the amount of gas in moles, R is the gas constant, and T is the absolute temperature in kelvin.
What is R in the ideal gas law?
R is the gas constant. This calculator handles the unit conversions automatically, so you never need to pick a value for R.
Can I use °C in the calculator?
Yes. The equation needs absolute temperature, so the calculator converts your °C or °F entry to kelvin automatically.
Can I mix pressure and volume units?
Yes. Mix units such as kPa with liters freely — pressure converts through pascals and volume through cubic meters before calculating.
What is the difference between absolute and gauge pressure?
Absolute pressure is measured from vacuum; gauge pressure is measured relative to the atmosphere. PV = nRT needs absolute pressure, so add atmospheric pressure to a gauge reading first.
When does the ideal gas law not work well?
It is an approximation that drifts at high pressure or low temperature, where real gases deviate more noticeably. It works best at relatively low pressure and higher temperature.