Step 1.Measure the lenght of their back from the base of the neck to the base of the tail.
Step2.Measure the width of their chest circumference or girth starts from the back of their front legs.
Step 3.measure the widht of their neck. When measuring the widht of their neck you must add an allowance that atleast one or two finger is fit enought to insert.
Step4.Next get the measurement from the underside of their collar up until 2 or 3 inches until where the private area is, This way you can keep them clean.
for the Different measurement of dogs based on their standard size chart MOREINFO