Calculate urine output rate (mL/kg/hr), convert units, check oliguria/anuria criteria and KDIGO 2012 AKI staging, and monitor hourly serial trends.
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Educational information — not medical advice.
This calculator helps you understand urine output numbers and the KDIGO 2012 criteria. Clinical interpretation, diagnosis, and treatment decisions may only be made by the healthcare professionals caring for the patient. If you or the patient experience a drastic drop in urine, contact health services immediately.
Usage note.
The results below are educational estimates from the numbers you enter. Accuracy depends on the precision of volume, weight, and duration measurements. Always confirm with the clinical team before acting on any number.
Urine output rate (mL/kg/hr)
—mL/kg/hr
Volume per hour: —
—
Anuria flag.
Total urine <100 mL within a 24-hour window meets the common definition of anuria. This is a finding that needs prompt evaluation by healthcare professionals.
KDIGO 2012 AKI criteria (urine output)
Calculation steps
Urine output unit converter
KDIGO 2012 AKI criteria checker
Enter the urine output rate and observation duration to check the AKI stage based on urine output criteria alone (creatinine criteria are assessed separately).
Hourly serial monitoring
Enter hourly urine volume (one value per line, in mL). The calculator computes the hourly rate, 6/12/24-hour rolling averages, trend, and KDIGO stage from the longest available window.
Hourly table
Summary
KDIGO 2012 AKI criteria table — urine output
Urine output criteria are assessed independently of serum creatinine criteria; meeting either one alone is enough for diagnosis and staging.
AKI stage
Urine output criteria
Stage 1
<0.5 mL/kg/hr for 6–12 hours
Stage 2
<0.5 mL/kg/hr for ≥12 hours
Stage 3
<0.3 mL/kg/hr for ≥24 hours or anuria for ≥12 hours
Common definitions: oliguria <0.5 mL/kg/hr (adults); anuria <100 mL/24 hr. Comparisons use strict thresholds (<): exactly 0.5 mL/kg/hr is at the boundary, not below it.
How do I calculate the urine output rate (mL/kg/hr)?
Urine output rate = urine volume (mL) ÷ body weight (kg) ÷ collection duration (hours). Example: a 70 kg patient producing 210 mL of urine in 6 hours → 210 ÷ 70 ÷ 6 = 0.5 mL/kg/hr, exactly at the KDIGO oliguria criterion threshold. The calculator above does this math automatically, along with conversion to mL/hr and a 24-hour projection.
What is the difference between oliguria and anuria?
Oliguria is reduced urine production: in adults <0.5 mL/kg/hr (in children the threshold commonly used is <1.0 mL/kg/hr). Anuria is more severe: practically no urine at all, generally defined as <100 mL per 24 hours. In KDIGO 2012 staging, anuria for ≥12 hours places the patient in AKI Stage 3 via the urine output criterion.
What is normal urine output for adults?
The general reference for adults is 0.5–1.5 mL/kg/hr, or roughly 800–2,000 mL per 24 hours depending on fluid intake. Values below 0.5 mL/kg/hr are called oliguria and become one of the diagnostic criteria for acute kidney injury (AKI) under KDIGO 2012 if sustained for ≥6 hours.
What are the KDIGO 2012 criteria for AKI based on urine output?
KDIGO 2012 defines three stages based on urine output alone: Stage 1 — <0.5 mL/kg/hr for 6–12 hours; Stage 2 — <0.5 mL/kg/hr for ≥12 hours; Stage 3 — <0.3 mL/kg/hr for ≥24 hours OR anuria for ≥12 hours. Serum creatinine criteria are assessed separately; meeting either criterion alone is enough for diagnosis.
Does oliguria always mean acute kidney injury (AKI)?
No. Oliguria can be caused by dehydration, low fluid intake, or a physiological stress response, and does not necessarily mean kidney damage. KDIGO requires a minimum duration of 6 hours precisely to filter out transient, non-specific drops in urine. Determining AKI still requires clinical assessment, including serum creatinine trends and the underlying cause.
What factors can confound urine output measurement?
Common confounders: diuretic drugs that raise urine volume and mask declining kidney function; catheter blockage or urinary obstruction that makes the collection look small; spills or recording errors; and using the wrong body weight (e.g. severe edema). A single measurement should always be read together with the hourly serial trend.
Can AKI occur even with a normal urine output rate?
Yes. Non-oliguric AKI is a real condition: kidney function declines (serum creatinine rises) while urine volume stays within the normal range. This is why KDIGO uses two legs of criteria — serum creatinine and urine output — assessed independently. Normal urine output does not rule out AKI.
Which body weight should be used: actual or ideal?
Common practice uses actual body weight, but in patients with severe edema or significant obesity some guidelines (e.g. the KHA-CARI adaptation of KDIGO) recommend using ideal body weight so the rate is not distorted. What matters most is consistency: record which weight is used each time you measure the serial trend.
What is polyuria and when should it be a concern?
Polyuria is excessive urine production, generally >3 liters per 24 hours (roughly >3 mL/kg/hr in adults). Causes vary, e.g. diuretic effects, uncontrolled diabetes mellitus, or diabetes insipidus. Like oliguria, polyuria is a finding that needs evaluation by healthcare professionals, not a self-diagnosis.
How often should urine output be monitored in critically ill patients?
In critically ill patients, hourly monitoring via urinary catheter is the standard because the KDIGO criteria themselves are based on 6-, 12-, and 24-hour windows. The Serial Monitoring tab in this calculator is designed for that pattern: enter the volume each hour, then see the 6/12/24-hour rolling averages, trend, and KDIGO stage from the longest available window.
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