Works out urine output per kilogram per hour, checks it against the KDIGO oliguria thresholds and gives the fluid balance.
Result
Enter the urine volume, the hours and the weight.
Sources
3 studies
3
studies
3,017
citations
839
PubMed papers
Evidence
Known limitations
In 75 medical ICU patients with urine output recorded hourly by a digital monitor, 55% had an episode of oliguria. Checking every hour or the total over 6 hours found similar episodes. The creatinine criterion diagnosed acute kidney injury in 28% of patients, and the urine criterion identified another 32%.
Nephrol Dial Transplant: Journal Metrics Score 1.2, Q2 · cited 200 times
PubMed · Free full text · DOI
In 317 critically ill patients with hourly urine output, adding the urine criterion raised the incidence of acute kidney injury from 24% (creatinine alone) to 52%. Oliguric patients without a creatinine rise had an ICU mortality of 8.8%, against 1.3% without acute kidney injury, and the diagnosis came earlier in oliguric patients.
Kidney Int: Journal Metrics Score 12.3, Q1 · cited 283 times
The RIFLE consensus set the urine output criteria still used today: below 0.5 mL/kg/h for 6 hours (risk), for 12 hours (injury), and below 0.3 mL/kg/h for 24 hours or anuria for 12 hours (failure).
Crit Care: Journal Metrics Score 7.4, Q1 · cited 6,903 times
PubMed · Free full text · DOI
The key guideline has been cited 3,017 times, and 839 PubMed articles mention urine output in mL/kg/h in their title or abstract. Citation counts from OpenAlex and article counts from PubMed, retrieved November 15, 2026. Journal Metrics Scores and quartiles are from this site’s current release; follow the journal name for details.
After the result
Low output · High output · Normal output
Check the catheter, then the patient. Find the cause of the diuresis. Keep measuring.
Next steps
Avoid common errors
5 common errors to avoid
and 3 more
Before you use the result
1An average hides hours
KDIGO wants output below the threshold throughout the period. A 6-hour total below 0.5 mL/kg/h can include normal hours.
2Catheter problems
A blocked or displaced catheter looks like oliguria. Check it before treating the patient.
3Weight in obesity
Using actual body weight in severe obesity labels more patients oliguric.
4Diuretics
Diuretics raise urine output and can hide acute kidney injury by the urine criterion.
5Children and newborns
Children use the same 0.5 mL/kg/h threshold for acute kidney injury, but newborns are often counted oliguric below 1 mL/kg/h, and the adult polyuria cut-off does not apply, so a high rate per kg may still be polyuria.
Formula
mL/kg/h = volume ÷ (weight × hours); below 0.5 for 6 hours or more meets the KDIGO urine criterion.
mL/kg/h = volume ÷ (weight × hours); below 0.5 for 6 hours or more meets the KDIGO urine criterion.
Formulas and KDIGO criteria
| Urine output | volume (mL) ÷ (weight (kg) × hours) = mL/kg/h |
|---|---|
| Projected 24 hours | volume ÷ hours × 24; above 3 L a day is polyuria in adults |
| Fluid balance | intake − urine − other measured losses, over the same period |
| Stage | Urine output |
|---|---|
| Stage 1 | Below 0.5 mL/kg/h for 6 to 12 hours |
| Stage 2 | Below 0.5 mL/kg/h for 12 hours or more |
| Stage 3 | Below 0.3 mL/kg/h for 24 hours or more, or no urine for 12 hours or more |
RIFLE and AKIN
Exact value
Polyuria
Test cases
3 published cases, each also a test case
3 published cases; the calculator reproduces every urine output.
Worked examples
A 62-year-old man weighing 64 kg developed stage 3 acute kidney injury with anuria the day after surgery for a type B aortic dissection and was started on continuous venovenous hemofiltration. On postoperative day 25 his urine output recovered to 730 mL in the day, and to 800 mL the next day.
“Urine output recovered to 730 mL (> 0.3 mL/kg/h) on POD 25 and 800 mL (> 0.5 mL/kg/h) on POD 26.”
730 mL / (64 kg × 24 h) = 0.475 mL/kg/h: above 0.3 but still below 0.5, as the authors said. The next day 800 mL gives 0.52 mL/kg/h. The weight is from admission; his weight on day 25 was not reported. The calculator would show stage 2 if sustained, but he was still on hemofiltration, which already counts as stage 3.
Entered as: Urine volume: 730 mL; Collection period: 24 hours; Body weight: 64 kg.
Source: Ge T et al., BMC Infect Dis 2026 (PubMed · Free full text · DOI)
A 44-year-old patient weighing 119.7 kg had a posterior lumbar interbody fusion under sevoflurane with propofol and remifentanil infusions. Preoperative kidney function was normal. Over the long operation urine output averaged 442 mL per hour, with fluids given at 434 mL per hour.
“Urine output ranged from 2.69 to 3.69 mL/kg/hour during these procedures”
The report gives hourly averages, so one hour is entered: 442 mL / (119.7 kg × 1 h) = 3.69 mL/kg/h, the highest in the series and well above the 2.5 mL/kg/h the authors used to define intraoperative polyuria. It would come to about 10.6 L a day.
Entered as: Urine volume: 442 mL; Collection period: 1 hours; Body weight: 119.7 kg.
Source: Georgakis NA et al., Cureus 2025 (PubMed · Free full text · DOI)
In the same series, a 75-year-old patient weighing 103.7 kg with coronary disease had a lumbar laminectomy, foraminotomy and facetectomy under sevoflurane with a ketamine infusion. Urine output averaged 316 mL per hour while fluids were given at 379.61 mL per hour.
316 mL / (103.7 kg × 1 h) = 3.05 mL/kg/h, as in the authors’ table. With intake entered, the hourly balance is 379.61 − 316 = +64 mL, before blood loss (300 mL over the whole operation) and insensible losses.
Entered as: Urine volume: 316 mL; Collection period: 1 hours; Body weight: 103.7 kg; Fluid intake (optional): 379.61 mL.
Source: Georgakis NA et al., Cureus 2025 (PubMed · Free full text · DOI)
FAQ
6 questions and answers
and 4 more answers
Questions
Divide the urine volume by the body weight and by the number of hours: mL/kg/h = volume (mL) ÷ (weight (kg) × hours). For example, 400 mL over 8 hours in a 70 kg adult is 400 ÷ (70 × 8) = 0.71 mL/kg/h.
For adults, 0.5 mL/kg/h or more is the usual target and the KDIGO threshold for acute kidney injury; about 0.5 to 1.5 mL/kg/h is typical. Less than 0.5 mL/kg/h is oliguria, and more than 3 L a day is polyuria.
KDIGO 2012: below 0.5 mL/kg/h for 6 to 12 hours is stage 1, below 0.5 mL/kg/h for 12 hours or more is stage 2, and below 0.3 mL/kg/h for 24 hours or more, or no urine for 12 hours, is stage 3. A rise in serum creatinine is the other way to meet the definition, and the higher stage of the two applies.
KDIGO asks for output below the threshold throughout the period, which strictly means hour by hour. In an ICU study, checking every hour and checking the total over 6 hours found similar numbers of oliguria episodes. This calculator uses the total over the period you enter and warns that an average cannot prove every hour was low.
KDIGO does not say. Most units use actual body weight. In severe obesity this makes mL/kg/h look low, so some clinicians use ideal or adjusted body weight; use the same weight consistently for one patient.
Fluid balance = total intake (oral, intravenous, feeds and drugs) − urine output − other measured losses (drains, nasogastric output, stool, blood) over the same period. Insensible losses from skin and breathing are not measured and are often estimated at about 500 to 1,000 mL a day in adults.
Further reading
7 references with PubMed and DOI links
7
references
5
free full text
From Kellum JA et al., Crit Care 2013 to the newest case reports.
References
clinical grade of aneurysmal subarachnoid hemorrhage, I to V.
total calcium adjusted for albumin, in mg/dL or mmol/L.
stroke severity from 15 bedside items, 0 to 42.
MAP from systolic and diastolic pressure, against the 65 mm Hg target.
eye, verbal and motor scores for preverbal children, 3 to 15.
oxygenation ratio with the Berlin ARDS severity ranges.
serum sodium corrected for high glucose, Katz or Hillier factor.
sodium − (chloride + bicarbonate), with the albumin-corrected gap.
urea nitrogen to creatinine ratio, in US or SI units.
estimated creatinine clearance with actual, ideal or adjusted weight.
cardiac output and index from oxygen consumption and saturations.
ANC from the white cell count, neutrophils and bands.
insulin resistance from fasting glucose and insulin, in US or SI units.
FENa from plasma and urine sodium and creatinine: prerenal, indeterminate or tubular pattern.
three-item stroke severity screen for large vessel occlusion, 0 to 4.
water deficit in hypernatremia from sodium, weight and body water.
expected PaCO2 in metabolic acidosis, 1.5 × HCO3 + 8 ± 2.
corrected QT interval by Bazett, Fridericia, Framingham or Hodges.
head CT decision rule for children with minor head trauma.
blood loss before hemoglobin or hematocrit reaches a chosen lowest value.
eye, verbal and motor response, 3 to 15, with GCS-Pupils.
Devine ideal body weight and adjusted weight from height and sex.
cuffed and uncuffed tube size and oral depth by age.
calculated osmolality, osmolal gap and ethanol correction.
severity of alcohol-associated hepatitis from prothrombin time and bilirubin.
MELD, MELD-Na and MELD 3.0 for chronic liver disease.
early stroke risk after a transient ischemic attack.
whether a patient with blunt trauma needs cervical spine imaging.
prognosis from a Bruce protocol exercise test.
alveolar–arterial oxygen gradient from a blood gas.
whether an adult with minor head injury needs CT.
risk of advanced liver fibrosis from age, AST, ALT and platelets.
6-week risk of a major cardiac event in emergency chest pain.
whether a pleural effusion is an exudate or a transudate.
cardiac risk before major noncardiac surgery, from six factors.
pre-test probability of pulmonary embolism, with the D-dimer step.
Contributed by Dr. Meng Zhao (MD · Former Neurosurgeon · Medical AI Researcher), from the original publications listed here. Last updated November 15, 2026. LinkedIn
The calculator code is tested against every worked example on this page before each release.
This calculator supports, and does not replace, clinical judgment. It is meant for healthcare professionals and is not medical advice for patients. Report an error through the contact page.