Where can I find how much free venting per lineal foot can I use for soffit material?

No sure I understand the question. Are you trying to find out how much soffit vent area you need for your attic...

I know how to calculate Attic venting, but having trouble finding info on actual material used in soffits. Aluminum perforated material to be specific. The 'free venting' area allowed by Code is the effective, actual venting taking place after restrictions due to screens, perforations sizes,. Looking for tested material results.