Strings for Braiding Leather
Braided Walking Stick Handle
Here is a general rule for determining the width and length of strings to be used in braiding or plaiting leather.
As a general rule for braiding or plaiting, the total string width for any number of strings needs to be 1½ times the finished circumference of the braid. This will vary a bit depending how much the strings stretch and narrow as they are being braided.
String length for round braiding and plaiting
As a general rule for braiding or plaiting, the length of each string (for any number of strings in the braid) needs to be about 1½ times the finished length of the braid plus the length needed at each end. A braider’s individual style will effect this rule a bit. A braider who tends to pull the strings outward will need a slightly longer string than a braider who pulls the strings straighter down the braid.
String length for a simple edge braid
A string length of about 2 times the length of the edge plus the length needed to finish the ends is generally adequate. I'd double that and add about 10% for a double edge braid.
To refine these general rules, I would take note of the length of string you begin a project with and deduct anything left over at the end and keep these notes for future reference.