All coats are individually made to measure to ensure the best fit.
When measuring, in imperial or metric (I’m of an age where I have learned both!) the coat length is from just behind where the collar sits, at the bottom of the neck and just forward of the shoulder blades to the base of the tail.
The waist measurement for a dog is taken from where the ribs end but not so far back that the strap covers his willy!
The strap can be a bit further back, around the stomach of a bitch.