Toy breeds, like the Chihuahua, develop and mature more quickly than large breed dogs. When born, a Chihuahua generally weighs between 2.5 and 5.5 ounces. The breed standard for the Chihuahua requires a maximum adult weight of 6 pounds.
Estimating Adult Size
The Chihuahua weight chart is a reliable guide for estimating a mature weight within a quarter of a pound. According to the chart, by Colonel V. D'Oyly Hammer in The Complete Chihuahua Encyclopedia, a Chihuahua puppy that weighs 3 ounces at birth will be approximately 3 pounds when full grown at 18 months. A 5-ounce newborn Chihuahua will weigh about 5.5 pounds at 18 months.
Tracking Weight Gain
A Chihuahua puppy will gain between 1 and 2 ounces per week until between 8 and 10 weeks old. Then, weight gain can increase 2 ounces - or a bit more - per week, until maturity at 18 months. Puppies may gain weight in "spurts," a fraction more one week, less the next. Monitor average weekly weight gain, with the optimum 18-month weight as a goal. Puppies that are larger at birth will generally be larger adults, and will gain more weight weekly than small puppies.
Reaching Full Size
Healthy puppies can gain weight steadily until they reach 90 percent of their estimated adult weight. Weight gain slows down around between 4 and 6 months, with some occasional growth spurts. Final adult weight depends on genetics, breeding and diet.
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A Chihuahua puppy should be fed following the quantity instructions on the dog food. Amounts differ depending on the food's protein content, and whether it is wet or dry food. When a Chihuahua's growth slows down, adjust food quantity to shift to an adult feeding schedule. It is important for a Chihuahua's health to avoid overfeeding and obesity.
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It is important to monitor the body weight and behavior of each individual Chihuahua puppy. A very active puppy may be thin and require additional calories. It is useful to chart your puppy's weight gain, watching for a consistently upward direction. Weight loss or an usual spike in weight gain may be cause for concern. Consult a veterinarian for professional advice.