Ideal Gas Law Calculator
PV = nRT
Answer
Ideal gas law problems look straightforward until you juggle pressure in atmospheres, volume in liters, temperature in Celsius, and a textbook that wants kelvin and pascals. Lab groups often redo worksheets because someone forgot to convert °C to K or mixed two different values of R. This calculator keeps the algebra, gas constant, and unit conversions in one place.
How to Use This Ideal Gas Law Calculator
- Choose what to solve for. Calculate P, V, n, or T; the output field locks while you enter the other three.
- Enter known values. Mixed pressure, volume, and temperature units are fine. n is in moles; temperature defaults to 20 °C.
- Set sig figs and Calculate. The answer appears in the panel and calculated field with the rearranged formula below.
Quick start: leave the mode on Calculate P | Given V, n, and T, enter volume and moles, set temperature (often 20 °C or 298 K), and read pressure. For STP volume problems, switch to Calculate V | Given P, n, and T.
Ideal Gas Law Formulas and Practical Applications
The ideal gas law links pressure, volume, temperature, and amount of gas in one equation—used in chemistry labs, intro thermodynamics, and rough engineering estimates when gases behave nearly ideally.
PV = nRT
P is pressure, V volume, n moles, T absolute temperature, and R the molar gas constant. This calculator uses R = 8.31446261815324 J/(mol·K) with P in Pa, V in m³, and T in K internally.
At STP, n = 1.00 mol and V = 22.4 L at about 1 atm illustrate the molar volume of an ideal gas. Rearrangements: P = nRT / V, V = nRT / P, n = PV / (RT), T = PV / (nR). Real gases deviate near condensation or high pressure; for force-on-area pressure, see the Pressure Calculator.
Standard Units
Pressure units
| Unit | Symbol | Notes |
|---|---|---|
| Atmosphere | atm | ≈ 101,325 Pa |
| mmHg / torr | mmHg, torr | ≈ 133.322 Pa |
| Pascal | Pa, kPa, MPa, GPa | SI pressure units |
| Bar | bar, dbar, mbar | 1 bar = 10⁵ Pa |
| psi / lb/ft² | psi, lb/ft² | US engineering units |
Volume units
| Unit | Symbol | Notes |
|---|---|---|
| Liter / mL | L, mL | 1 L = 1 dm³; 1 mL = 1 cm³ |
| Cubic SI | cm³, dm³, m³ | m³ pairs with Pa and R in J/(mol·K) |
| US customary | ft³, in³ | HVAC and engineering |
Amount and temperature
Amount n is always in moles (mol). Temperature accepts °C, °F, K, or °R and converts to kelvin internally—you do not add 273.15 by hand. Kelvin must stay above absolute zero.
Frequently Asked Questions
What is the ideal gas law?
PV = nRT links pressure, volume, amount, and absolute temperature for gases where molecular volume and intermolecular forces are negligible.
What value of R does this calculator use?
R = 8.31446261815324 J/(mol·K) after converting to pascals and cubic meters. Textbook R ≈ 0.08206 L·atm/(mol·K) is equivalent when units match—this tool converts for you.
Which variable can this calculator solve for?
Any one of P, V, n, or T; enter the other three.
Can I mix unit systems?
Yes—psi, liters, and °F together work; values convert to SI internally before solving.
Why must temperature be absolute?
Gas pressure scales from absolute zero, not the Celsius or Fahrenheit zero. The calculator accepts °C, °F, K, or °R and converts to kelvin automatically.
For pressure from force and area, use the Pressure Calculator. Browse all physics calculators on RapidRatio.
Disclaimer. Informational only—not professional engineering, chemical process, or laboratory advice. Real gases deviate from ideality; verify critical measurements with calibrated instruments and qualified analysis.