Pups can usually be fitted into an adult coat at 8-9 months with room to grow into based on your measurements & variable pup growth. Whippet's are a slow maturing dog, & will be 85% of their adult size by 8 months. They will continue to fill out until around 18 months of age. Please refer to the PUP coat for more information. Fior larger pups have a look at our KISS coats. Why do whippet's need special martingale collars?