My advice, which is free and worth every penny. I give refunds to boot.
1. Measure everything in metres. Much easier to calculate, fewer errors.
2. Figure out your wingspan, arms spread, fingertip to fingertip. This will allow you to very quickly measure out long pieces. Figure out your hand span, and you can whip out a piece of almost any length in just a few seconds.
3. For a racquet you are going to string more than once, disassemble the strings carefully and measure the pieces. Add about 40 cm for knots on main, about 30 cm for crosses. This is because you can tie off on the top and not waste much for the first starting knot on the crosses. Write it all down.
4. Keep a piece of each type in case you need to bridge with your starting clamp.
5. Subtract about 5% for multi and synthetic gut since they stretch and you'll need a little less.
As mentioned earlier, if you are careful and a little frugal, you should be able to squeeze at least on additional full stringing, maybe that and a hybrid piece, from each reel.
Good luck.