How tall is a full grown yellow lab on 4 legs?

Your query seems to contain a misconception. Yellow labs, like other breeds of dogs, have four legs regardless of their age. The height of a full-grown yellow lab can vary depending on the individual dog's genetics and overall size. On average, male yellow labs typically stand between 22 and 24.5 inches (56 to 62 centimeters) tall at the shoulder, while female yellow labs are usually between 20 and 22.5 inches (51 to 57 centimeters) tall at the shoulder.