Jack russel needed for university study. Questions

Hi everyone. I am new to this forum. I am a third year university student studying applied zoology and wondered if a few of you may be able to help me. I have an assignment on morphology and I have decided to base it on back lengths in relation to coat sizing. I came up with this because I really struggle to find coats to fit my JRT, according to the sizes on the coats she should be a small but a small absolutely drowns her. I can't be the only person with this problem? If anyone is will to help I would be so great fun it will only take minutes. I will post instructions below with an image that can act as a guide. Thank you so much in advance.
Using a tape measure, measure the length of your dogs back from the nape of the neck to the base of the tail in cm's.
Please respond to this thread with measurement, age and gender.
Thanks so much for helping me compete my study.

I don't have Jack Russells, but this is an interesting topic, so I hope you don't mind my comments. I have sold a lot of dog coats in a former life.
<-- My girl has two coats, a sturdy Danish mac with a removable fleece jacket, which is marked as 16" , and lightweight softshell coat, marked size 18" , and both fit perfectly. IMO, you really need to know which measurement system the manufacturer is using. When there were fewer designs it was usual to lift the dog's head, and measure from the base of the neck to the base of the tail. Even this simple method can have flaws as, for example, a Springer Spaniel and a Bulldog could have the same back measurement, but a completely different girth fitting. The shape of the animals spine can be another complicating factor, ie Bedlington, or Italian Greyhound.
There are now a multitude of coat designs, and some manufacturers are using a collar to tail-base measure. If a customer measures their dog using this measurement, but the manufacturer is one that uses the other system, the coat is probably going to be a couple of inches too big. For this reason, I would always want to actually try the coat on the dog to be sure of a comfortable fit, or deal with a manufacturer who provides a foolproof measuring guide - which usually means one of the more expensive brands.
Good luck with your survey.