Is there a quick way to calculate whether or not the attic is balanced for a re-roofing project?

Here is some information about quickly calculating if the attic has enough attic ventilation.

The most accurate method to determine whether or not the attic is balanced with sufficient intake vents and exhaust vents is physically count the vents after measuring the attic square footage. There isn't an easy way to determine if the attic is balanced at a glance because of the various checkpoints associated with identifying a balanced system (are the intake vents free and clear, are the holes for all vents properly cut, etc.). However, here are two handy rules of thumb you can use:  Linear feet of ridge vent (exhaust vent) x 2 is the amount of linear feet of intake vents needed (whether the intake vent is The Edge Vent, Vented Drip Edge or Continuous Soffit Vents). For every roof louver (exhaust vent) being used install one 8" x 16" undereave vent (intake vent) because they both provide approximately the same Net Free Area (About 50-60 square inches of NFA each). A 1-to-1 ratio will thus be balanced.