About the Urine Output Calculator
Hourly urine output is one of the simplest and most sensitive bedside markers of kidney perfusion. Nurses and doctors in intensive care, theatre recovery and the wards chart it in millilitres per kilogram per hour (mL/kg/hr) so that patients of different sizes can be compared against the same thresholds. This calculator divides the total urine collected by the patient’s weight and the length of the collection.
Enter the volume measured, the number of hours it was collected over and the body weight. You get urine output in mL/kg/hr and mL/hr, a projected 24-hour volume, and a check against the KDIGO acute kidney injury (AKI) urine criteria: below 0.5 mL/kg/hr for 6–12 hours (stage 1), for 12 hours or more (stage 2), and below 0.3 mL/kg/hr for 24 hours or more or no urine for 12 hours (stage 3).
KDIGO itself notes it is not settled whether the urine criteria mean an average or a persistent reduction over the period. This tool uses the average rate over the whole collection, so a period of normal output followed by a sudden drop can be hidden. Staging AKI also uses serum creatinine, and catheter blockage, diuretics and fluid status should always be considered.
With the default inputs, the urine output is 0.43 mL/kg/hr. Change any value above to recalculate instantly.
How to use the urine output calculator
- 1Add up the urine volume measured over the period (catheter bag or measured voids).
- 2Enter how many hours the collection covers.
- 3Enter the patient’s weight in kg or lb.
- 4Read the mL/kg/hr result and the KDIGO check.
- 5Recheck hourly and look at the trend and serum creatinine.
Formula and method
The total urine volume is divided by the collection time to give mL per hour, then by body weight to normalise for size. Pounds are converted to kilograms by multiplying by 0.4536. The projected 24-hour volume simply scales the hourly rate to a full day.
KDIGO 2012 defines the urine output criteria for acute kidney injury as: stage 1, below 0.5 mL/kg/h for 6–12 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 anuria for 12 hours or more. The check here compares the average rate and collection length with those thresholds.
- volume
- Total urine collected (mL)
- weight
- Body weight (kg)
- hours
- Length of the collection period
Worked examples
70 kg adult, 180 mL in 6 hours
180 mL ÷ (70 kg × 6 h) = 0.43 mL/kg/hr, below 0.5 for 6 hours — the KDIGO stage 1 urine criterion. That is 30 mL/hr, versus the 35 mL/hr (210 mL over 6 h) needed for 0.5 mL/kg/hr.
Normal output over 24 hours
1,800 mL ÷ (80 kg × 24 h) = 0.94 mL/kg/hr, or 75 mL/hr — comfortably above the oliguria threshold.
Severe oliguria, weight in pounds
154 lb is 69.85 kg. 400 mL ÷ (69.85 × 24) = 0.24 mL/kg/hr, below 0.3 for 24 hours, which meets the stage 3 urine output criterion.
Frequently asked questions
What is normal urine output in mL/kg/hr?+
For adults, at least 0.5 mL/kg/hr is the usual minimum target, and typical output is around 0.5–1.5 mL/kg/hr. Infants and young children normally produce more, and many pediatric units use 1 mL/kg/hr as the lower limit.
What urine output counts as oliguria?+
In adults, oliguria is usually defined as less than 0.5 mL/kg/hr sustained for 6 hours or more, or under about 400 mL per day. Anuria means essentially no urine output.
How does KDIGO stage AKI by urine output?+
KDIGO stage 1 is below 0.5 mL/kg/h for 6–12 hours, stage 2 is below 0.5 mL/kg/h for 12 hours or more, and stage 3 is below 0.3 mL/kg/h for 24 hours or more or anuria for 12 hours. Creatinine criteria are assessed alongside.
Should I use actual or ideal body weight?+
KDIGO 2012 does not specify; it lists actual, ideal and lean body weight as an open research question. Actual weight is the common bedside choice. In obesity, actual weight can over-diagnose oliguria, so some clinicians also look at the result using ideal or adjusted body weight.
What should I check first when urine output drops?+
Rule out mechanical causes first — a kinked or blocked catheter, or urinary retention with a bladder scan — then review fluid balance, blood pressure, medications and serum creatinine.
For healthcare professionals and education only. This calculator implements a published formula or score but is not a diagnosis and does not replace clinical judgment. Verify inputs and results against the original source before using them in patient care.