I've seen ads for garter ties being 36" length for 'regular' calves (whatever that is anyway) and 48" for big calves.

I measured mine and tried wrapping the measuring tape around as if it was a tie and 36" wouldn't even tough the ends, 48" did the trick nicely.

So judging by the OP calf photo, I would venture about the same length of finished tie?

When you braid, you loose a significant amount from your original length.