The question will open up a can of worms. Everyone and each manufacturer
measures it differently. If you a concerned about carrying a knife in
a particular jurisdiction, see if in the law it even gives a definition.
I think it is from blade tip to where blade meets the bolster.
This is a minor detail but this is the site where members are interested in the details.
Presuming the answer usually is from the bolster to the tip like I've always believed, do you include the length of tang covered by a swing guard? While I prefer that length not be included, to stay safe I'd include it if I needed to meet a legal requirement.