How do you know how many feet of christmas lights you need for your tree?

I'm seeing most on amazon.ca from like 60 feet to 100 feet. That seems...like way too much. Do much come in segments you can detach? It doesn't say so on the product page.

edit: i have about a 7-8 foot tree, and some places online say you'd need 700-1000 lights?!

https://www.lowes.com/projects/other-activities/decorate-christmas-tree/project

The most popular one on amazon.ca is 200 lights but 100 feet long. Should I have more..light/ft density? They're LEDs.