How many nephrons are in each kidney?

Inside each of your kidneys are tiny working units called nephrons—and each kidney has about one million of them. These microscopic structures are the key players in filtering blood, removing waste, and producing urine.

Each nephron has two main parts: the glomerulus, which is a small group of blood vessels that acts like a filter, and the tubule, which processes the filtered fluid. As blood passes through the glomerulus, waste products, extra water, and small molecules like salts are filtered out. The fluid then moves through the tubule, where the body reabsorbs what it still needs and sends the rest out as urine.

Together, the nephrons in both kidneys filter about 180 liters (48 gallons) of blood per day. They adjust what to keep and what to remove based on your body’s needs at any given moment. This constant adjustment helps maintain the right balance of fluids, salts, and other important substances in your blood.

Interestingly, not all nephrons are active at the same time. Some stay on standby and can take over if others become damaged. This built-in backup system helps explain why people can live with one kidney and why kidney problems may not show symptoms until many nephrons are no longer working.

As you age, the number of functioning nephrons naturally decreases, which is one reason kidney function can decline over time. Keeping your blood pressure and blood sugar in check can help protect your nephrons for the long term.

Understanding how many nephrons you have—and what they do—offers a clearer picture of how your kidneys work to keep your body in balance every day.

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