It's as long as you need to tie up whatever you need to tie up with a little extra left over.
When I need a piece of string to tie up newspapers, it's a lot smaller than the piece of string I need to tie my plastic chair to the dock so it doesn't blow into the lake.
HOWEVER (and this is very important....) no matter HOW much you have to tie up, you can never use a full ball of string w/o cutting it. To do so elimates any "pieces" of string as a full ball is a "whole".
