Engin Exam · Free practical tool

Ideal gas calculator

Rearrange the ideal-gas equation while keeping pressure absolute and converting temperature to kelvin. Select the missing variable explicitly so extra example inputs cannot overdetermine the problem.

Free results and workingNo signupLocal calculations
Your inputsCalculated on your device

Example values loaded. Replace them with your own measurements.

Your result
↗

Make the numbers make sense.

Enter your values, choose the units, and calculate. You’ll see the result and the working here.

Free results. No account needed.

The method

pV = mRT, with temperature converted to kelvin and absolute pressure in pascals.

Before using the result

  • Ideal gas approximation; use a gas-specific R. The target field is ignored and solved. No real-gas compressibility or condensation model.

Worked examples

These original training examples illustrate the method for United States: Fundamentals of Engineering (FE) Examination. Use the matching “Load example” button above to explore a variation; example values are not equipment settings or prescribed criteria.

1. Worked example

Rearrange the ideal-gas equation while keeping pressure absolute and converting temperature to kelvin. Select the missing variable explicitly so extra example inputs cannot overdetermine the problem.

Solve for
Pressure
Gas mass
1 kg
Specific gas constant (J/kg·K)
287.05
Gas volume
1 m³
Absolute-temperature input
20 °C
  1. mR = 287.05 J/K.
  2. T = 293.15 K; pV = 84148.7075 J.
  3. Solve pV = mRT for pressure.
  • Absolute pressure: 84,148.71 Pa
  • Volume: 1 m³
  • Temperature: 20 °C

2. Comparison example

Compare a different supplied condition using the same method. For Engin Exam, the important check is that the input meaning, units and method assumptions still match the problem.

Solve for
Pressure
Gas mass
2 kg
Specific gas constant (J/kg·K)
287.05
Gas volume
1 m³
Absolute-temperature input
20 °C
  1. mR = 574.1 J/K.
  2. T = 293.15 K; pV = 168297.415 J.
  3. Solve pV = mRT for pressure.
  • Absolute pressure: 168,297.4 Pa
  • Volume: 1 m³
  • Temperature: 20 °C

Check your understanding

1. Which relationship is used?

pV = mRT, with temperature converted to kelvin and absolute pressure in pascals.

2. Which assumption should you check first?

Ideal gas approximation; use a gas-specific R. The target field is ignored and solved. No real-gas compressibility or condensation model.

3. How should you verify a different unit system?

Convert every input to the displayed calculation units first. Equivalent physical inputs must give equivalent results; a unit label alone does not convert a number.

Continue with the matching exam topic

This tool connects to United States: Fundamentals of Engineering (FE) Examination free practice. Work through a question independently, then use the calculation steps to identify where your method differs. The tool stays free whether or not you choose paid preparation.