For a 5 hour event we estimate at least 3 glasses per person and more if you can afford. People rarely take their empty glass back to the bar and servers tend to pick up partially empty glasses from cocktail/dinner tables. We suggest a wine glass per person because guests may have a cocktail first, and then wine with dinner. Beer glasses are usually 1/3 of the number of guests, as beer drinkers tend to take the bottle. For mixed drink glasses, estimate 1 or 2 per guest.
So, for 100 guests = 100 Wine/35 Beer/165 All-Purpose Glasses
For plated meals, you will obviously need water goblets for the guest count; a wine glass for each guest if wine is served tableside; and a champagne glass per person if doing a champagne toast. Please note that these glass totals are over-and-above the glassware on the bar.
Ultimately, glassware totals are affected by cash vs. open bar; the length of the event; the time of day; the day of the week; the type of event; the age and gender of your guests; the weather and other factors, so just share your event details with us and we can help you plan.