Compressor Power Calculator
Compressor power is calculated from the thermodynamic work of compression. This calculator uses the isentropic (adiabatic) compression formula, which represents the theoretical minimum power for compressing a gas from inlet pressure to discharge pressure. The actual shaft power is the isentropic power divided by the isentropic efficiency. Enter inlet temperature, pressure ratio, mass flow rate, specific heat ratio, specific heat at constant pressure, and isentropic efficiency.
Isentropic compressor power formula
Wis = m × Cp × T1 × [(P2/P1)(k-1)/k - 1]
Wshaft = Wis / etais
T2s = T1 × (P2/P1)(k-1)/k
Where: m = mass flow rate (kg/s), Cp = specific heat at constant pressure (J/kg.K), T1 = inlet temperature (K), P2/P1 = pressure ratio, k = isentropic exponent (Cp/Cv), eta_is = isentropic efficiency, T2s = isentropic discharge temperature (K).
Design notes
- For multistage compression, equal pressure ratios per stage minimise total power for a given overall pressure ratio.
- Intercooling between stages reduces power consumption by returning the gas to approximately inlet temperature before the next stage.
- ASME PTC 10 provides the standard test procedure for compressor performance measurement.
- Add a mechanical transmission efficiency factor (typically 95% to 98%) to account for gearbox and bearing losses.
Compressor power calculator: frequently asked questions
What is isentropic compression power?
Isentropic power is the ideal power required for adiabatic (no heat transfer) reversible compression. The formula is W_is = m_dot * Cp * T1 * [(P2/P1)^((k-1)/k) - 1], where m_dot is mass flow (kg/s), Cp is specific heat at constant pressure (J/kg.K), T1 is inlet temperature (K), P2/P1 is pressure ratio, and k is the specific heat ratio (Cp/Cv).
What is isentropic efficiency?
Isentropic efficiency eta_is = Isentropic power / Actual shaft power = W_is / W_shaft. For centrifugal compressors, typical isentropic efficiencies range from 70% to 85%. For reciprocating compressors, 70% to 90%. The shaft power accounts for mechanical losses in addition to gas compression.
What is the specific heat ratio k for air?
For dry air at ambient conditions, k = Cp/Cv = 1.40. At higher temperatures (above 300 degrees C), k decreases. For natural gas (primarily methane), k is approximately 1.31. For steam, k is approximately 1.13. The value of k significantly affects the calculated power.
What is polytropic compression?
Polytropic compression follows the law P * V^n = constant, where n is the polytropic index. For ideal isentropic compression, n = k. For actual compression, n differs from k due to heat transfer and irreversibilities. Polytropic efficiency is often used for multistage compressors and gas turbines.
How do I convert from volumetric to mass flow rate?
Mass flow rate (kg/s) = Volumetric flow rate (m^3/s) * density (kg/m^3). For ideal gas, density = P / (R_specific * T), where P is pressure (Pa), R_specific is the specific gas constant (287 J/kg.K for air), and T is temperature (K). At standard conditions (101.325 kPa, 15 degrees C = 288.15 K), air density is 1.225 kg/m^3.
Official sources
- ASME PTC 10-1997 Performance Test Code on Compressors and Exhausters: ASME PTC 10.
- NIST WebBook Thermophysical Properties: webbook.nist.gov/chemistry/fluid/.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.