How to Size Air Compressor According to Factory Capacity （Full Pressure & Airflow Calculation Formula）

Many factory owners purchase air compressors only based on power, leading to two major losses: insufficient airflow shuts down production lines, while oversized units waste thousands of dollars on electricity every year. This post shares international standard sizing formulas for screw air compressors. Factory managers, purchasing staff and engineers can calculate the right model within 3 minutes.

1. Confirm Required Working Pressure (Bar / PSI)

Different industries require different air pressure:

1.Woodworking, metal polishing, regular painting, auto repair shop: 7–8 Bar

2.Laser cutting, plasma cutting, high-precision CNC machine: 10–13 Bar

3.Sandblasting, mining drill rig, bottle blowing machine: 12–16 Bar

Sizing Rule: Compressor rated pressure = Equipment working pressure + 1~2 Bar (to offset pipeline pressure loss) Example: Laser cutter requires 10 Bar air supply, you need a 12 Bar compressor.

2. Core Airflow Calculation (m³/min / CFM)

FAD (Free Air Delivery): Real air output marked on nameplate, the only standard for selection. Unit conversion: 1 m³/min = 35.31 CFM

Calculation Formula: Total Basic Air Demand = Sum of air consumption of all pneumatic machines × Simultaneity Factor

Simultaneity Factor Reference:

Small workshop (≤5 air tools): 0.8–0.9, most machines work at the same time

Medium factory (5–15 production machines): 0.6–0.7, machines run in shifts

Large production line (over 15 machines): 0.4–0.5, staggered operation

Practical Calculation Example: Hardware painting workshop: 4 spray guns (0.3 m³/min each) + 2 pneumatic grinders (0.2 m³/min each) Simultaneity factor = 0.8 Total raw airflow = 4×0.3 + 2×0.2 = 1.6 m³/min Basic air demand = 1.6 × 0.8 = 1.28 m³/min

3. Add Expansion & Air Leakage Margin

Reserve airflow for future production expansion and natural pipeline leakage: Final Compressor Required FAD = Total Basic Air Demand × 1.1 ~ 1.2 (10%-20% extra) Example: 1.28 × 1.15 = 1.472 m³/min You need a compressor with FAD ≥ 1.472 m³/min.

4. Power & Airflow Reference Chart (8 Bar Working Condition)

7.5kW(10HP): 1.0~1.2 m³/min

15kW(20HP): 2.0~2.3 m³/min

37kW(50HP): 5.0~5.5 m³/min

75kW(100HP): 10.0~11.0 m³/min

110kW(150HP): 15.0~16.0 m³/min

5.  Common Costly Sizing Mistakes

1.Skip simultaneity factor, buy oversized machine with 30% extra capacity, huge power waste;

2.Ignore pipeline pressure loss, insufficient air pressure reduces finished product yield;

3.Judge by theoretical displacement instead of FAD value on nameplate, actual air output is far lower;

4.No extra airflow reserved, need to buy a second compressor within 1-2 years after factory expansion.