The best way I have found to measure my longer snake it to let them roam and if the stretch out completely or close to it, remember where the snake starte and stopped and measure that area. If find they have a better chance of going completely straight if they are in a corner like on the couch or where the floor meets the wall. Sometime while holding them if you grab closer to the tail they might dangle straight enough or if they are in your arms just try to maneuver them so they stretch out a little. Isn't the easiest thin to do at times though.