You can also get a piece of clear, rigid tubing (Home Depot, Lowes, or order a set of snake restraining tubes) and mark it off in inch-long increments. Coax your snake to crawl through the tube - obviously you want tubing longer than your snake here - and mark off head & tail once your snake is completely inside and stretched out. Easy as pie...well...with ball pythons anyway. I don't suggest trying this method on something like a retic unless you've got access to giant tubing & a lotta lubing!!!

K