Is my Yorkie too skinny around the waist? What's a normal weight?

From the photos, he looks just fine. You should be able to feel his ribs. If you can see them, he is too thin. If you have shaved his coat for the summer to keep him cooler, please know that a dog's coat insulates against heat as well as cold, so there is no need to do it. The full coat also is some protection against mosquito and tick bites.

It really depends on how she looks. If you can see her ribs than she is too thin and you should feed her more food. You could either increase the amount twice a day or add in a feeding and feed her three times a day. If you are unsure than have your vet take a look at her.

I recommend googling Purina body condition scoring chart and determining if the the degree to which you can see and feel her ribs is consistent with the lower body condition scores. If so, increasing her daily food ration slightly and re-assessing her body condition score in 2-4 weeks is advised. Good luck!

Pictures can be very deceiving and i recommend you use a body condition scoring chart (there are many versions online) to help assess and ask your vet nurse if you are unsure. Although he does not appear unhealthy, he is quite narrow across his back and core muscles. Be sure to maintain him on a good quality puppy food until 15mintgs and consider an assessment by a physiotherapist to ensure there are no underlying causes and to advise on suitable exercise. A chiropractic assessment may also be worthwhile to see if there are any issues preventing him from developing

Sadly, overweight pets are so common that those actually at a healthy body weight may appear too thin to many people. As a general rule of thumb, a dog or cat’s ribs should be easy to feel under a *thin* fat covering, but should not be visible or difficult to feel. Additionally, a dog or cat should have a visible “waistline” with a tuck up in their abdomen. Your veterinarian can assess the body condition scores of to provide a more objective measurement of your pet’s weight, but tools like the [PetCoach Healthy Pet Weight Calculator](https://www.petcoach.co/healthy-weight-calculator/) can also help to guide pet owners at home. Maintaining a healthy weight is crucial to a pet’s health, as obesity can lead to an increased risk of developing heart disease, diabetes and a number of other health conditions.

You should be able to feel the bones with gentle pressure over the ribs and spine. Without a photo, I can't say by looking what kind of body condition she has, but from the description above twelve pounds is a good-size Chihuahua. This chart may help you visualize if she is underweight or not. https://www.aaha.org/public_documents/professional/guidelines/weightmgmt_bodyconditionscoring.pdf

Have Pebbles examined by your veterinarian to diagnose any medical causes such as intestinal parasites, malabsorption or maldigestion issues. Once she is cleared medically, you can try increasing the amount of food being fed. Switching to a "hotter" (higher protein) food should be done gradually to prevent gastrointestinal upset. Canidae, Acana, Orijen, Taste of The Wild and the Royal Canin line are all premium diets. The website www.dogfoodadvisor.com is an excellent resource for comparing diets.