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Air Compressor Calculators

Specific Power Calculator

Calculate a compressor's specific power (kW per 100 CFM or kW per m³/min) to compare efficiency.

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About this calculator

Specific power is the standard efficiency metric used to compare air compressors of different sizes and brands — it expresses how much electrical power is needed to deliver a given amount of compressed air. A lower specific power means a more efficient compressor at that pressure.

Formula

Specific Power (kW/(m³/min)) = Input Power ÷ FAD; kW/100 CFM = Specific Power × 2.8317
  • kWCompressor electrical input power — kilowatts
  • FADFree air delivery — m³/min
  • Specific PowerEfficiency metric — kW per m³/min or kW per 100 CFM

Worked Example

Given: A compressor draws 15 kW input power and delivers 3 m³/min FAD.

Result: Specific power = 15 ÷ 3 = 5.0 kW/(m³/min), equivalent to about 14.2 kW/100 CFM.

How to Use

  1. Enter the compressor's actual measured or rated electrical input power in kW.
  2. Enter its free air delivery (FAD) in m³/min.
  3. Click Calculate to see specific power in both kW/(m³/min) and the commonly quoted kW/100 CFM.

Important Assumptions

  • Specific power varies with discharge pressure — always compare compressors at the same rated discharge pressure.
  • Uses input (not isothermal or shaft) power for a real-world efficiency comparison.

Common Mistakes

  • Comparing specific power figures for compressors rated at different discharge pressures, which is not a fair comparison.

Frequently Asked Questions

What is a good specific power value for a screw compressor?

Modern efficient screw compressors at around 7 bar typically range roughly 5.5–6.5 kW/(m³/min); values vary by pressure, technology and size, so always compare at the same discharge pressure.

Why does specific power matter for buying a compressor?

A compressor with lower specific power costs less to run over its life even if its purchase price is higher — this metric lets you compare true running efficiency, not just size or price.

These calculators are provided for informational and estimation purposes. Results depend on the assumptions and input values used. Always verify critical engineering calculations against applicable standards, manufacturer specifications, site measurements, and qualified professional advice.