Start with a saddle height that allows you to pedal gently with one heel on the pedal, that leg going entirely straight at the bottom of the pedal stroke with the hips not rocking. It's easier to do while the bike is stopped and you're leaning against something. That knee should be completely locked out with the heel on the pedal. This height will be within ~4mm of perfect for you. Some like it a little higher, some a little lower, depending on their preferred ankle angle.

I never measure or use a formula. Measure with your leg. Even transferring measurements from one bike to another doesn't work because the seat tube angle may be different, pedals may be different, saddle model may be different, saddle setback may be different, etc.