All you need to measure your dog for their new coat is a soft tape measure and perhaps a dog treat to keep them on their best behaviour whilst you take their measurements. Dog coats are sized according to two types of measurements, back length and torso circumference. In order to take representative measurements, you'll need to make sure your dog is standing up. If they're sat down, their weight will shift downwards and (depending on the dog) can result in an inaccurate measurement.
Measuring Your Dog's Back
To measure the back of your dog, place the start of your tape measure on the back of your dog's neck and measure all the way down until the base of their tail. Take this measurement in centimetres.