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Pediatric Urine Output Calculator

Enter urine volume, weight and collection time to find the output rate.

How it is calculated

The tool divides the collected urine volume by body weight and by the length of the collection: rate = V / (W × t), where V is volume in mL, W is weight in kg and t is the collection period in hours. It also scales the hourly rate to a day: rate × 24, in mL/kg/day. Weight and hours must be above zero and volume cannot be negative. Results are shown with two decimals. The tool only calculates the number; it does not say whether the rate is normal, because the acceptable range depends on the child's age and clinical situation, so compare it with your unit's protocol.

Worked example

A child weighing 12 kg produces 120 mL of urine over 8 hours. Weight times hours: 12 × 8 = 96. Rate: 120 / 96 = 1.25 mL/kg/hr. Scaled to a day: 1.25 × 24 = 30.00 mL/kg/day. The same 120 mL in an 8 kg child would be 1.88 mL/kg/hr, which shows why the weight adjustment matters.

Try this example →

Common mistakes

  • Entering weight in pounds; the rate is per kilogram, so convert first.
  • Entering the collection time in minutes. The divisor is hours, so 90 minutes is 1.5.
  • Using the volume of a single void for a long period, or the 24-hour volume with a short number of hours.
  • Including diaper or catheter bag contents measured at a different time than the stated period, so volume and hours do not match.
  • Reading the daily figure as a measured 24-hour output. It is only the hourly rate multiplied by 24, so it assumes the rate stays constant.

About this calculator

Urine output normalized to body weight and time — expressed in mL/kg/hr — is a core bedside indicator of renal perfusion and hydration status in children, since kidney output responds quickly to changes in blood volume and blood pressure. Adequate output is generally considered to be at least 1 mL/kg/hr in infants and young children, with a somewhat lower threshold around 0.5 mL/kg/hr often used for older children and adolescents; sustained output below the relevant threshold is termed oliguria and prompts closer clinical evaluation.

This calculator takes urine volume, the child's weight, and the collection time period, and returns the output rate in mL/kg/hr. Pediatric ICU and ward nurses, and pediatricians monitoring a hospitalized child's fluid balance use it to standardize output tracking across patients of very different sizes, since a raw milliliter count means little without adjusting for body weight — this is a monitoring calculation, not a diagnostic or treatment tool.

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