How to Size a Rotary Screw Compressor (HP & CFM Guide) | Wemano

1.Why Proper Sizing Matters:

• Choosing the right rotary screw compressor

  isn’t just about power—

  it’s about matching air demand with efficiency.

• Too small, and your tools lose pressure;

too large, and you waste electricity every hour.

2.Understanding Key Terms: HP, CFM, and PSI:

💡:A 20 HP rotary screw compressor usually delivers around 80–90 CFM at 125 PSI.

3.How to Calculate Your Air Demand:

Step 1: List all air tools or machines

Example:

• Impact wrench – 10 CFM

• Paint sprayer – 12 CFM

• Air dryer – 5 CFM

Step 2: Add a safety margin (25–30%)

Step 3: Match with compressor output:

For example:

Total air demand = 40 CFM × 1.3 ≈ 52 CFM
→ Choose a 10–15 HP rotary screw compressor.

Reference:Engineering Toolbox-Air Consumption Chart.

4.HP vs CFM — What’s the Right Ratio?

A general rule from CAGI (Compressed Air & Gas Institute):

Every 1 HP produces 3–4 CFM at 100 PSI.

Wemano Tip: Don’t oversize your compressor. Instead, combine a medium-size unit with a receiver tank for demand peaks.

Learn more:Air compressor tank Guide.

5.When to Choose Rotary Screw over Piston Compressors?

If your business runs multiple shifts or needs stable pressure, a rotary screw compressor offers long-term savings.

Compare real applications:Rotary Screw Compressor Advantages Over Piston Compressors.

6.Real-World Sizing Examples:

📈 A properly sized Wemano rotary screw compressor can save up to $800 per year in energy compared to an oversized unit.

7.Common Sizing Mistakes:

• ❌ Ignoring peak demand.

• ❌ Selecting by HP only.

• ❌ Forgetting about dryer and filtration losses.

• ❌ No allowance for future expansion.

Always use CFM at working pressure, not “maximum CFM” in brochures.

8.Final Checklist Before Purchase:

Confirm total air demand (CFM)

• Check voltage and phase.

• Include air dryer and filter pressure drop.

• Choose proper tank volume.

• Consider noise and space limits.

💡 Need expert help sizing your system?

→ Contact Wemano Technical Team

Summary:

A well-sized rotary screw compressor gives you:

• Reliable air supply.

• Lower maintenance costs.

• Energy efficiency.

• Longer equipment life.

Download this HP & CFM guide (PDF) — Blue-White Professional Edition, Wemano.