Calculators
Ideal Gas Law Calculator
Solve PV = nRT for pressure, volume, moles, or temperature.
Solve PV = nRT for one unknown. Inputs use absolute pressure, liters, moles, and Celsius; calculations convert to SI units and absolute temperature internally.
Result
101.326672 kPa
The ideal gas law is a model. Real gases can deviate substantially at high pressure, low temperature, near phase changes, or when intermolecular effects are important.
About This Tool
The ideal gas law connects four state variables of a gas: absolute pressure P, volume V, amount n, and absolute temperature T. This calculator rearranges PV = nRT to solve any one of those variables from the other three. The interface uses kPa, liters, moles, and degrees Celsius for convenient entry, then converts pressure, volume, and temperature to compatible SI quantities before applying the universal gas constant. The result is useful for classroom problems and first-pass estimates when ideal-gas behavior is a reasonable approximation.
How To Use It
- Choose the variable you want to solve for.
- Enter the other three quantities. Pressure must be absolute pressure, not gauge pressure.
- Enter temperature in degrees Celsius; the calculator converts it to kelvins before using the gas equation.
- Review the result and the ideal-gas assumptions before applying it to a real system.
Examples
One mole near room temperature
At 25 °C, one mole occupying about 24.465 L corresponds to approximately 101.325 kPa absolute pressure under the ideal model.
Molar volume near 0 °C
At 0 °C and 101.325 kPa, one ideal mole occupies about 22.414 L.
Find amount of gas
For 10 L at 100 kPa and 26.85 °C (300 K), n = PV/(RT) ≈ 0.401 mol.
Useful Notes
The ideal gas equation
PV = nRT. Solving for each variable gives P = nRT/V, V = nRT/P, n = PV/(RT), and T = PV/(nR). This tool uses R = 8.31446261815324 Pa·m³/(mol·K).
Temperature must be absolute
Gas-law ratios require absolute temperature. Celsius values are converted with T(K) = T(°C) + 273.15. A non-positive kelvin temperature is physically invalid for this model.
Use absolute pressure
PV = nRT uses absolute pressure measured relative to vacuum. A gauge pressure reading must be converted to absolute pressure by accounting for the surrounding atmospheric pressure before it is used.
Unit consistency
The calculation converts kPa to pascals and liters to cubic meters so the SI gas constant can be used consistently. Results are converted back to the interface units for readability.
When the ideal model works best
Ideal-gas behavior is generally a better approximation at relatively low pressure and sufficiently high temperature, away from condensation and critical regions. The acceptable error depends on the gas and purpose.
Real-gas limitations
Real molecules occupy space and interact. At high pressure, low temperature, or near phase transitions, an equation of state or compressibility-factor method may be needed. This calculator does not model gas identity, humidity, reactions, mixtures, phase equilibrium, or measurement uncertainty.
FAQ
What does R mean in PV = nRT?
R is the universal gas constant. This calculator uses 8.31446261815324 Pa·m³/(mol·K), which is equivalent to 8.31446261815324 J/(mol·K).
Can I use gauge pressure?
Not directly. The ideal gas law requires absolute pressure. Convert gauge pressure to absolute pressure first.
Why is Celsius converted to kelvins?
The gas law requires an absolute temperature scale. Celsius has an arbitrary zero and cannot be used directly in PV = nRT.
Is the ideal gas law exact?
No. It is an idealized model. Real-gas deviations can become important depending on pressure, temperature, gas identity, and proximity to a phase change.
Can I use this for air?
It can provide an ideal-gas approximation for air when conditions are appropriate, but it does not account for humidity, changing composition, or non-ideal effects.
Related Tools
Molarity Calculator
Solve molarity, moles, volume, or solute mass using M = n/V.
Pressure Converter
Convert Pa, kPa, MPa, bar, psi, atm, mmHg, and Torr.
Volume Converter
PopularConvert liters, gallons, cups, fluid ounces, and cubic units.
Temperature Converter
PopularConvert Celsius, Fahrenheit, and Kelvin temperatures.