HeyBub wrote:

I have a 1500 sf house. How many sf should I have in soffit vents?

According to my corrected calculations, (...)

I think it's a complete waste of time to mess around with calculations
for roof venting that is probably based on ad-hoc forumulas to begin
with.

Rule #1 for roofs/attics is that you can't have too much ventilation.

Beyond that, assuming that you have eves in the first place, any
logically-designed roof and eve system will have an eve vent-hole
located between every roof joist (assuming the eves were originally
finished with plywood on their underside instead of aluminum).

Now it's probably the case for new construction (new = anything younger
than 20 years) that the eves were not finished with solid plywood but
instead were simply clad in aluminum - and if so it should have been
100% perforated aluminum.