What this calculator does
Urine output is usually monitored not as a raw volume but as a rate relative to body weight and time, because a healthy output for someone weighing 50 kilograms is a different number from a healthy output for someone weighing 100 kilograms. This calculator takes a volume, a body weight and the hours over which the volume was collected, and returns the rate in millilitres per kilogram per hour, which is the standard way normal urine output is expressed and compared against reference thresholds.
The figure most often cited as a warning line is oliguria, commonly defined as urine output below about 0.5 mL/kg/hr in adults, sustained over a period of hours rather than a single reading. That threshold comes from clinical literature and is included here for context, not as a diagnosis: a low reading can reflect dehydration, a genuine kidney problem, or nothing at all if it is a one-off measurement.
The formula
Divide the urine volume collected by the body weight in kilograms, then divide again by the number of hours the volume was collected over. The result is the standard mL/kg/hr rate used in clinical monitoring, which is then compared against the commonly cited normal range and the oliguria threshold.
| Term | Meaning |
|---|---|
| Output rate | Urine volume divided by body weight and by hours: mL ÷ kg ÷ hr. |
| Oliguria threshold | A sustained output below roughly 0.5 mL/kg/hr in adults, a commonly cited clinical warning level. |
| Collection period | The number of hours the volume figure was actually measured over, not a single spot check. |
The inputs explained
| Field | What to enter |
|---|---|
| Urine volume collected (mL) | The total urine volume collected, in millilitres. |
| Body weight (kg) | Body weight in kilograms. |
| Hours over which it was collected | The number of hours the volume above was collected over. |
When to use it
Checking a single reading against the normal range
A one-off volume and weight, converted into mL/kg/hr, tells you roughly where that reading sits against the commonly cited normal range, as a starting point rather than an answer.
Tracking output over a shift or a day
Adding up volume collected over several hours and dividing by that longer window smooths out the noise of any single void, which matches how output is actually monitored clinically.
Comparing output before and after a fluid change
Running the same weight and time window before and after an intravenous fluid adjustment shows whether output moved in the expected direction, as one input among several a clinician would look at.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the output rate changes with urine volume, at a fixed weight and time
A 70 kg body weight and a 4-hour collection window, across a range of urine volumes.
| Volume collected | Urine output rate | Band |
|---|---|---|
| 50 mL | 0.18 mL/kg/hr | Below the commonly cited 0.5 mL/kg/hr oliguria threshold |
| 100 mL | 0.36 mL/kg/hr | Below the commonly cited 0.5 mL/kg/hr oliguria threshold |
| 140 mL | 0.50 mL/kg/hr | Within the typical normal range |
| 200 mL | 0.71 mL/kg/hr | Within the typical normal range |
| 300 mL | 1.07 mL/kg/hr | Within the typical normal range |
| 500 mL | 1.79 mL/kg/hr | Within the typical normal range |
How the output rate changes with body weight, at a fixed volume and time
A fixed 200 mL collected over 4 hours, across a range of body weights.
| Body weight | Urine output rate | Band |
|---|---|---|
| 40 kg | 1.25 mL/kg/hr | Within the typical normal range |
| 55 kg | 0.91 mL/kg/hr | Within the typical normal range |
| 70 kg | 0.71 mL/kg/hr | Within the typical normal range |
| 85 kg | 0.59 mL/kg/hr | Within the typical normal range |
| 100 kg | 0.50 mL/kg/hr | Within the typical normal range |
| 120 kg | 0.42 mL/kg/hr | Below the commonly cited 0.5 mL/kg/hr oliguria threshold |
Questions
What is considered normal urine output?
A commonly cited normal range for adults is roughly 0.5 to 1.5 mL/kg/hr, sustained over several hours rather than judged from a single void. Individual variation is wide, and factors like fluid intake, heat, medication and kidney function all move it.
What does a low reading actually mean?
A single low reading is common and often means nothing more than someone recently emptied their bladder or has not drunk much fluid. A sustained low rate over several hours, particularly below the 0.5 mL/kg/hr oliguria threshold, is the pattern clinicians pay attention to, alongside other signs.
Why measure output relative to body weight instead of just millilitres?
A fixed volume like 100 mL an hour means something very different for a 45 kg adult than for a 110 kg adult. Expressing output as mL per kilogram per hour puts people of different sizes on the same scale, which is why it is the standard clinical unit.
Should I use this calculator instead of seeing a doctor?
No. This tool works out a rate and shows it against a commonly cited reference threshold; it cannot assess causes, take a history, or examine anyone. Any real concern about urine output, especially a sudden or sustained drop, needs an actual clinical assessment.
For the related concept of proportional daily figures, see the pro rata calculator. For other kidney-related monitoring figures, see the urine protein-to-creatinine ratio calculator.