Why urine output is measured
Urine output is one of the simplest signs of how well the kidneys are perfused and working. In intensive care, after surgery, in sepsis or with heart failure, nurses record it every hour, often from a urinary catheter. A falling output can be the first sign of acute kidney injury, before blood creatinine rises.
The calculation
Urine output (mL/kg/h) = volume ÷ weight ÷ hours
The calculator also shows the hourly volume, the volume projected over 24 hours and the minimum hourly volume that corresponds to 0.5 mL/kg/h for that weight.
Worked example
An adult weighing 155 lb (70.3 kg) has produced 600 mL of urine in 12 hours:
| Result | Value |
|---|---|
| Urine output | 0.71 mL/kg/h |
| Per hour | 50 mL/h |
| Projected over 24 hours | 1,200 mL |
| Minimum for 0.5 mL/kg/h | 35 mL/h |
This is above the 0.5 mL/kg/h threshold, so it does not meet the urine output criterion for acute kidney injury.
KDIGO criteria for acute kidney injury
The KDIGO guidelines (2012) use both creatinine and urine output. For urine output in adults:
| Stage | Urine output |
|---|---|
| 1 | Below 0.5 mL/kg/h for 6 to 12 hours |
| 2 | Below 0.5 mL/kg/h for 12 hours or more |
| 3 | Below 0.3 mL/kg/h for 24 hours or more, or no urine for 12 hours or more |
The stage is the worst one reached by either creatinine or urine output. The calculator uses the collection time you enter, so make sure the volume covers the whole period.
Other targets
- Children: infants usually produce 1 to 2 mL/kg/h and older children about 1 mL/kg/h. Pediatric definitions of oliguria differ from adult ones.
- Burns: fluid resuscitation is often adjusted to reach 0.5 to 1 mL/kg/h in adults.
- Polyuria: an output of more than about 3 liters a day in an adult is considered high and may point to diabetes, diuretics or diabetes insipidus.
Pitfalls
A blocked or kinked catheter can mimic a sudden drop in output, so check it before drawing conclusions. In people with severe obesity, using actual weight can make output look falsely low; some teams use ideal or adjusted weight. Diuretics raise output without meaning that the kidneys are recovering.
This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.