How many nephrons does a human kidney contain?

Each human kidney contains approximately 1,000,000 to 1,250,000 nephrons. These structures serve as the functional units of the kidney, responsible for filtering blood and producing urine.123

In the context of renal system disease, the progressive destruction of these units is a common feature of chronic renal failure, where the number of functional nephrons may be reduced to less than a 20th of the normal amount.4