We actually made three turkeys and three hams and green beans mashed potatoes gravy rolls and stuffing and they had some left over and that was for 110 people

Ah, my we all have such different answers. When I was cooking in an institutional kitchen, we always planned 1/2 of turkey per person. That was 1/2 pound of the uncooked turkey. It feed folks very generously.

Additionally, I would think that you would need to take into consideration the other items being served. If there is ham in addition to the turkey, you need less turkey. How many sided dishes are being served?

Also, are you plating the meals or is this a buffet. Plating, you can be more exact with quantities. Buffet, I always tend to error on the high side.

If you are serving a buffet, if the Turkey is that the beginning of the line, you will need more turkey, than if it is the last item.

Finally, what is the age of the people being served. If they are fifty and over 1/2 pound per person is probably reasonable. If they are mostly 12 to 35, then I would allow for 1 pound per person.

Figure 1.5lbs per person

I would do a minimum of three.

Consider a serving 1 pound per person. 5 20lb. turkeys should work for 100 people.

I think you will need at least 15 turkeys. 10 Turkeys should feed 100 people, but 15 will leave room for leftovers. People love to take an extra plate home.