I use a few online programs one of them being serpwidgets snake measurer. It is super easy to use. You need a measurement tool like a ruler or a length of string you know the exact measurements of and the snake itself. Take a full body (not balled up) picture of your snake next to the measurement tool and upload it to the website and measure. There is also an app call the snake ruler for both android and iphone... I personally do not like it as my fingers are bigger then the pictures and there are a few workable bugs but otherwise it works.