Remove your pet's collar and use a brush to smooth the fur around his neck. Brush the pet's back from the shoulders to the base of the tail. Smoothing all of the fur allows for an accurate measurement.
Using a tape measure, have your pet stand and measure along the top of his spine from the base of the neck where it joins the body—usually where his collar sits—to the base of his tail. For male pets you may have to adjust the measurement. If the clothing you’re buying doesn’t have a cut out for his groin and belly, you might want to shorten the length a bit to minimize the chances he’ll urinate on his new clothes. If your pet is between sizes, choose the larger size.
This is the measurement around the largest part of your pet’s rib cage, usually just behind the front legs. Measure closely all the way around his chest when he’s standing. To get the right amount of snugness, use the 'two-finger rule' by slipping two fingers between the measuring tape and your pet. If your pet is between sizes, choose the larger size.
This is the circumference of your pet’s neck, generally where the collar sits. Position the tape measure from the pet’s withers—the ridge between the shoulder blades— to the top of his chest. Then measure all the way around your pet’s neck, holding the tape measure closely. Use the two-finger rule. If your pet is between sizes, again, choose the larger size.