Labrador Retrievers are classified as a medium large breed. A male Labrador will typically reach a height of 22-24 inches, though some males have been known to grow up to 30 inches tall. Male Labradors are typically much larger than female Labradors, both in height and in weight. A male Labrador will also build up muscle slightly faster than a female Labrador, which may cause a rapid increase in total body mass.
A female Labrador Retriever will grow to be about 21-23 inches tall, depending on several environmental factors (such as nutrition, age when spayed, hormonal functions). Female Labrador Retrievers are a bit smaller than male Labrador Retrievers, though are more prone to becoming overweight. This is mostly due to different active hormones, and a slightly slower metabolism. A spayed female Labrador Retriever is much more likely to become overweight than a Labrador with functioning reproductive organs.
Due to their size, some Labrador Retrievers may have growth abnormalities that result in joint problems. This is one of the reasons that some Labrador Retrievers develop hip, knee, and elbow dysplasia. During puppy growth, some Labradors can actually increase in size too rapidly, which causes poor formation of the bone structure.