Sizing a screw compressor correctly is the difference between stable production and constant pressure problems. If the machine is too small, equipment starves for air. If it is too large, the plant pays for unused capacity and may experience short cycling.

Understand the Basic Units First

• CFM and m³/min: both describe volumetric flow. 1 m³/min equals approximately 35.3 CFM.
• PSI and Bar: both describe pressure. 1 Bar equals 14.5 PSI.
• kW and HP: both describe motor power. 1 HP equals approximately 0.746 kW.

Calculate Total Air Demand

• List every machine that uses compressed air.
• Record its required pressure and average air consumption.
• Determine the simultaneous peak demand rather than simply adding every nameplate value.
• Add a reserve of around 20% for leakage, tool wear, and future expansion.

The resulting total flow is the basis for selecting a screw air compressor that matches the plant’s real operating profile. A proper screw air compressor capacity calculation also considers the pressure required at the most demanding point in the distribution system.

Select the Correct Pressure

Pressure is not the same as flow. Raising system pressure increases energy consumption and leakage loss, so the plant should run at the lowest pressure that still satisfies the most demanding machine. If one process needs 8 Bar while others need 6 Bar, a dedicated boost solution may be more efficient than running the entire network at 8 Bar.

Why Demand Patterns Matter

If air demand varies significantly during the day, a variable speed screw compressor can reduce energy waste by matching output to consumption. Sizing should therefore include both the maximum demand and the typical operating range, not only the largest single moment.

Correct sizing lowers capital cost, energy cost, and downtime. When in doubt, work from measured air consumption data rather than rough estimates.