How Many Lights Do I Need?
Typically, count on 100 lights per vertical foot of tree. For example: for a 7 foot tree, you will need at least of 700 lights. I prefer 150 per foot (or 1050 lights for a 7 foot tree) for a more "twinkly" look.
Of course, if your tree is fuller than average you will also need more lights than on a slender tree.