Urine Output Calculator

Calculate your urine output rate in mL/kg/hr from a measured volume, body weight, and collection time, then see where it falls on the KDIGO oliguria and AKI staging scale.

Quick Facts

Formula
Rate = Volume / (Weight x Time)
Urine output rate in mL/kg/hr, the standard clinical unit for oliguria and AKI screening.
Normal threshold
0.5 mL/kg/hr or higher
Sustained output below this level for 6 or more hours meets KDIGO oliguria criteria.

Your Results

Calculated
Urine output rate
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mL per kg per hour
Hourly volume
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Average mL per hour
Projected 24-hr volume
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At this rate (mL)
KDIGO classification
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Oliguria / AKI staging

Ready

Enter the collected volume, body weight, and collection time, then calculate the urine output rate.

About the urine output calculator

Urine output is one of the simplest and most widely tracked measures of kidney function and fluid status, especially in hospitals and critical care. This calculator applies the standard formula — collected volume divided by body weight and time — to express output as milliliters per kilogram per hour (mL/kg/hr), then places that rate against the KDIGO (Kidney Disease: Improving Global Outcomes) urine-output criteria used to stage acute kidney injury (AKI).

The formula

Urine output rate (mL/kg/hr) = urine volume (mL) ÷ [body weight (kg) × collection time (hours)]. Weighting by body size lets the same absolute volume mean something different for a 50 kg person and a 100 kg person, and dividing by time turns a single measurement into a rate that can be compared across shifts or collection windows.

KDIGO oliguria and AKI staging

  • Normal: output at or above 0.5 mL/kg/hr.
  • Stage 1: output below 0.5 mL/kg/hr sustained for 6 to 12 hours.
  • Stage 2: output below 0.5 mL/kg/hr sustained for 12 hours or more.
  • Stage 3: output below 0.3 mL/kg/hr for 24 hours or more, or no urine output (anuria) for 12 hours or more.

When to consult a professional

This tool performs the standard urine-output arithmetic for education and record-keeping; it is not a diagnosis. Low urine output can reflect dehydration, obstruction, medication effects, or acute kidney injury, and the right response depends on the full clinical picture. Anyone concerned about persistently low urine output should contact a healthcare provider.

Frequently Asked Questions

What formula does this urine output calculator use?
It divides the collected urine volume by body weight and collection time to give a rate in milliliters per kilogram per hour (mL/kg/hr): rate = volume ÷ (weight × time). This mL/kg/hr rate is the standard unit used in clinical urine-output monitoring.
What counts as normal urine output versus oliguria?
A rate at or above 0.5 mL/kg/hr is generally considered normal for adults, which works out to roughly 800 to 2,000 mL over 24 hours for a typical adult depending on body size and fluid intake. Oliguria means urine output sustained below 0.5 mL/kg/hr.
How does this calculator apply KDIGO staging?
It follows the KDIGO urine-output criteria for acute kidney injury: Stage 1 is output below 0.5 mL/kg/hr for 6 to 12 hours, Stage 2 is the same rate sustained for 12 hours or more, and Stage 3 is output below 0.3 mL/kg/hr for 24 hours or more, or no urine output for 12 hours or more.

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