I just spent a good amount time tonight going over my spreadsheet for the running rigging. This sheet includes every line on the boat both ones I need to replace immediately before the masts go back up (topping lifts, running back, etc) and lines that I can wait to do when we get our sails. It also includes all the blocks, eyes, and shackles. Obviously it also includes the diameter, length of line, type of line, etc.
The thing you also want factor in is the type of splices you’ll be doing and how much length you need for that. For shorter lines this can be a significant percentage portion of the overall length you need.
For example, I need a 6’ x 5/16” Amsteel line with an eye in each end. A single Class 2 12 Strand Eye Splice (NOTE: how long is a fid) in this line takes 16.5” of line and in this example I’m going to have 2 such splices so while the total working line I’ll end up with will be 6’ long I’ll need 8’ 9” of line in order to make the splice. I am leaving out the distance to wrap the eye, but in this case that is nominal.
Ideally when you were buying line online they’d have calculators that include the splice.