What horsepower do you need? 3.5 CFM average per hp.

What CFM air delivery do you need? (CFM or M3/Min)

Please refer to compressor selection tables.

What discharge air pressure, pounds per square inch (PSIG / BARG ) do you need?

What are the electrical requirements voltage-phase-hertz are at your installation site?

Voltage:115, 220, 208, 230, 380, 460, 575, etc. single or three phase and 50 or 60 hertz?

Is the compressed air usage intermittent if so use a small piston compressor or constant use a rotary

What percent of the day do you need constant air flow if more then 75% or over a 15 hp think rotary?

What type of equipment are you running on air, do you need a compressed air dryer?  

What quality of air do you need? oil and water free, then make sure you see our air dryer sections