For the first 8 feet of a Christmas tree, each foot needs at least 12 medium/standard sized ornaments per foot totaling:
2 foot= 24 ornaments
3 foot= 36 ornaments.
4 foot= 48 ornaments.
5 foot= 60 ornaments.
6 foot= 72 ornaments.
7 foot= 84 ornaments.
8 foot= 96 ornaments.
As the tree grows in height the base grows in width so…
For 9 and 10 ft. trees you need to add 18 ornaments for each of the bottom feet
9 foot=18+96=114 ornaments.
10 foot= 18+ 114=132 ornaments.
For 11 and 12’ trees add 24 ornaments for each of the bottom feet
11 foot=24+132=156 ornaments.
12 foot= 24+156=180 ornaments.
…and for each additional foot after 12’ add 30 ornaments each.
Important note- If you are mixing sizes of ornaments and using a lot of tiny, small, medium, large, and huge ornaments, these numbers will go up or down based on the sizes of ornament.
You should only use 1 huge ornament per foot or per 2 feet of tree.
If you are interested in my post on How to Decorate a Christmas Tree Like a Professional click here.