A healthy kidney weighs about 5 ounces, according to Dartmouth-Hitchcock Medical Center. The Mayo Clinic backs up this statement, claiming that a kidney normally weighs less than one-third of a pound.
Certain medical conditions can alter the weight of a kidney from its normal, healthy weight. For example, the Mayo Clinic describes a condition known as polycystic kidney disease, which causes non-cancerous cysts to grow inside the kidney. Cysts are sacs filled with watery fluid and can become quite large and heavy. According to the Mayo Clinic, a kidney containing a large number of these cysts potentially weighs as much as 30 pounds.