Long Tail Cast-On length

[HamaLee]

This is absolutely my favorite cast on method, it creates a really nice even cast-on row for me. However, I have a problem judging how long to leave for the tail....especially when I have to cast on a lot of stitches.

For example, this project needed me to cast on 126 stitches and I tried to judge and had to rip and re-cast 3 TIMES because I kept running short! Even when I thought I was taking a ton more yarn.

Now I've cast on and I've got this ridiculously long hangy-tail end. So how do you all figure out how long of a tail to leave when casting on a loooottttttt of stitches?