Madison Area Herpetological Society

Making Sure Your Animal Measures Up!

How to Measure Your Snake/Other Reptile!
By Eric Roscoe

Another very commonly asked question and subject many reptile and amphibian hobbyists, enthusiasts, and pet owners have about their animal(s) is how long they are, or otherwise, how to accurately measure them in terms of their length. Luckily, this quick article will highlight and cover some of the most commonly used and accurate methods for doing so. When it comes to reptiles and amphibians, there are two most commonly used terms and definitions in terms of measurement. SVL (or snout-to-vent length), is most often used in terms of lizards and crocodilians, which measures the animal’s length from the tip of its snout to its ventral scale and opening and does not include the length of the tail. STT (or snout to tail length) is the other commonly used term, and is most often applied to for snakes, which are generally not as prone to losing and/or regenerating their tails from their ventral and sub caudal regions as many lizards are. This is likewise also the reason why lizards are more often measured in SVL length. As for turtles, tortoises, and other chelonians, most measurements are taken by measuring the length anterior to posterior wise of the carapace (which is the hardened, bony or in some species, cartilaginous dorsal or upper portion of a chelonian’s shell and skeletal structure) and typically not counting the length of the head, neck, or tail as they can typically be withdrawn in most species and do not contribute significantly to the animal’s overall measurable length. With this said, here are some commonly used ways and criteria to measure your animal!

Sheddings/Shed Skins: While sheddings and shed skins can oftentimes be thought of as an accurate and easy way of measuring an animal’s size or length, they are actually not the most accurate means of doing so. In most cases, a snake’s shedding can expand anywhere from 10 to 30% or more due to the pressure and friction put on it during and after the animal sheds. Therefore, this often makes their sheds longer or larger than the animal truly is, leading to at least some misperception about the animal’s size.

Tape Measures, Measuring Sticks, or Rulers: Tape measures and various types of measuring sticks can be a somewhat more accurate and precise method for obtaining the current length of an animal, but depending on the make/model/or brand, can be inflexible and difficult to work over and around an animal’s body curvature and usually require the animal to be held and restrained by two or more people as straightly as possible.

Ball of Yarn/String/Twine: Using a ball of yarn, string, or twine is perhaps the most reliable and newly emerging method for accurately measuring your reptile. This typically involves gently restraining an animal behind the head to restrict its movements somewhat (particularly if the animal is venomous, or otherwise defensive and prone to biting) and using the assistance of one to two other people to slowly and carefully unravel the ball of material down the animal’s neck and body to the end of the tail (or ventral area if measuring by SVL) using the thumb or fore finger to pinpoint intervals along the body. The line can then be cut and measured or then be measured from the end of the specified area of the animal to gain its most accurate length. The flexibility of this method can often easily work over and around an animal’s body curvature without the need for additional restraint in holding the animal perfectly straight (although this can still be done using this method).

Some Applications and Computer Software: Finally, there are some newly emerging computer software programs and other electronic applications (or apps for short) that have become popular in recent years. Typically most of what is required by these for best results is obtaining an overhead full body photograph of the animal intended to be measured on a flat surface and another object of known size, length, and dimensions included in the photo that can be used by the program as a matter of perspective and reference. Serpentine Widgets is an example of one of these programs, which can also measure the ratios of how much a shedding has spread or expanded. There are overall a few simple considerations to keep in mind when taking a photo for this purpose for best results.