You've done all this before, ain't ya?Tie a rig the full length of your top kit whether that's a 2 piece or match top 3.
Starting with an 18cm winder put the rig on and count the number of turns round the winder. If it comes to say 7.5 complete turns then write it down on a piece of paper.
Do the same with your next section added and write it down on a piece of paper.
If you have some longer floats that need a longer winder like a 20 or 22cm winder do exactly the same and write it down on a piece of paper.
I think you can see where we're going here.
Counting in arms lengths is daft. You could be built like Peter dinklage or Peter crouch!