How big should a 12 week old boxer mastiff mix breed be?

The size of a 12-week-old Boxer Mastiff mix breed can vary depending on the individual puppy's genetics and overall health. However, a general guideline is that at 12 weeks, a Boxer Mastiff mix puppy might be around 15-20 inches tall at the shoulder and weigh 20-30 pounds. Please note that these are approximate measurements and actual size may vary.