What Is the Normal Bladder Capacity in Adults and Children?

The bladder is a muscular organ that holds urine before it is passed out of the body. While most people understand its basic function, many are unsure about how much urine it can actually store. The normal bladder capacity varies based on age, body size, and overall health.

In healthy adults, the average bladder holds about 400 to 600 milliliters of urine—roughly 13 to 20 fluid ounces. Most people begin to feel the need to urinate when the bladder is about half full, typically at 150 to 200 milliliters (5 to 7 ounces). The urge becomes stronger as the bladder fills, but the body can usually hold urine for several hours, depending on hydration levels and muscle control.

The bladder expands gradually and sends signals to the brain when it is time to empty. It is designed to stretch and relax as needed, but regularly delaying urination for too long can put strain on the bladder muscles and affect normal function over time.

In children, bladder capacity is much smaller and increases with age. A rough estimate for children’s bladder capacity can be calculated using a simple formula:

• Bladder capacity in milliliters = (Age in years + 2) × 30

For example, a 5-year-old child would be expected to have a bladder capacity of around 210 milliliters. Infants and toddlers urinate more frequently because their bladders hold less, while older children gradually gain better control as their bladder muscles and nervous system mature.

It is normal for young children to urinate more often during the day and sometimes during the night. Bedwetting in children under the age of 5 is usually not considered a problem. However, frequent urination, urgency, or inability to hold urine beyond the expected age may suggest issues such as overactive bladder, urinary tract infections, or delayed bladder development.

In both adults and children, any noticeable change in how much urine the bladder holds—or how often it needs to be emptied—should be discussed with a healthcare professional. Early evaluation can prevent complications and improve quality of life.