🎈 Ideal Gas Law Calculator (PV = nRT)
Enter any three of pressure, volume, moles and temperature, and the ideal gas law PV = nRT gives the fourth.
Amount
0.999381 mol
PV = nRT with R = 0.082057 L·atm·K⁻¹·mol⁻¹, use atm, L, mol, K. 🔒 Computed in your browser.
How the ideal gas law calculator (pv = nrt) works
The ideal gas law relates pressure (P), volume (V), amount (n) and temperature (T): PV = nRT, with R = 0.082057 L·atm·K⁻¹·mol⁻¹. Enter any three quantities in the matching units (atm, L, mol, K) and the tool rearranges the equation to solve for the fourth: P = nRT/V, V = nRT/P, n = PV/RT and T = PV/nR. As a check, one mole of gas at 273.15 K and 1 atm occupies 22.41 L, the familiar molar volume at STP.
Use absolute temperature in kelvin (°C + 273.15) and consistent units. With R in L·atm/(mol·K), pressure is in atm and volume in litres.
Frequently asked questions
What is the ideal gas law?
PV = nRT, relating a gas’s pressure (P), volume (V), number of moles (n) and absolute temperature (T), where R is the gas constant. It describes an ideal gas well at ordinary temperatures and low-to-moderate pressures.
What value of R should I use?
It depends on units. This tool uses R = 0.082057 L·atm·K⁻¹·mol⁻¹, so pressure is in atmospheres, volume in litres, amount in moles and temperature in kelvin.
How do I solve for each variable?
Rearrange PV = nRT: P = nRT/V, V = nRT/P, n = PV/RT, T = PV/nR. Enter the three you know and the tool computes the fourth.
Why must temperature be in kelvin?
The gas law requires absolute temperature; 0 K is absolute zero. Convert Celsius with K = °C + 273.15 before entering it.
When does the ideal gas law break down?
At high pressure or low temperature, where real-gas interactions matter; then equations like van der Waals are more accurate. For typical classroom and lab conditions the ideal law is a good approximation.
What volume does one mole of gas occupy at STP?
About 22.4 L at 0 °C (273.15 K) and 1 atm: V = nRT/P = 1 × 0.082057 × 273.15 ÷ 1 = 22.41 L. This molar volume is a handy sanity check.
Can I use different pressure or volume units?
Only if you switch R to match. With R = 0.082057 L·atm/(mol·K) you must use atm and litres; for kPa and litres use R = 8.314, and for mmHg R = 62.36. This tool is set up for atm, L, mol and K.
How do I find the density or molar mass of a gas from PV = nRT?
Substitute n = mass ÷ molar mass to get PV = (mass/M)RT, which rearranges to M = (mass·R·T) ÷ (P·V) and density = PM ÷ RT. So measuring pressure, temperature and a gas’s density gives its molar mass.
What is the difference between the ideal gas law and the combined gas law?
The ideal gas law PV = nRT relates all four state variables at one condition and includes the amount of gas (n). The combined gas law links an initial and final state of a fixed amount of gas, so n cancels and R is not needed.