Ideal Gas Law Calculator

Engineering calculator reviewed for preliminary design use · Last updated: March 2026

Solve ideal gas law PV = nRT for any one unknown from the other three: pressure, volume, moles, or temperature. Apply to gas state change calculations, tank sizing, and compressor calculations as a fundamental engineering tool.

Ideal Gas Law Calculator (PV = nRT)

The ideal gas law PV = nRT describes the relationship between pressure, volume, moles, and temperature for an ideal gas. While real gases deviate at high pressures and low temperatures, this equation is widely used in engineering calculations.

Variables

P: Absolute pressure [Pa] (gauge pressure + atmospheric)
V: Volume [m³]
n: Amount of substance [mol]
R: Gas constant = 8.314 J/(mol·K)
T: Absolute temperature [K] (°C + 273.15)

Applications

Tank gas inventory and fill calculations
Gas cylinder content estimation
Flow rate conversion between conditions
Compressor suction/discharge state calculations

Frequently Asked Questions

When does the ideal gas law fail?

The ideal gas law becomes inaccurate at high pressures (>10 bar), low temperatures (near boiling point), and for large polyatomic molecules. Use van der Waals, Peng-Robinson, or other real-gas equations for these conditions.

What is the value of the gas constant R?

R = 8.314 J/(mol·K) = 8.314 kPa·L/(mol·K). When using different pressure or volume units, ensure R is in consistent units. Common error: mixing bar with Pa or liters with cubic meters.

Editorial Responsibility

Last reviewed: March 2026
Reviewed by: EngiCompute Editorial Team
Intended for preliminary engineering use

These results are preliminary estimates for screening-level design use. They do not replace detailed engineering, code compliance verification, or vendor-certified calculations.