Urine Output Calculator: ml/kg/hr From Volume, Time and Weight

Urine output in ml/kg/hr is the amount of urine divided by the hours it was collected over, divided by body weight in kilograms: urine output = volume (ml) ÷ time (hours) ÷ weight (kg). Normal adult output is about 0.5 to 1 ml/kg/hr, roughly 35 to 70 ml an hour at 70 kg.

The urine output formula

• Dividing the volume by the hours gives ml an hour; dividing that by weight gives ml/kg/hr.
• Convert minutes to hours by dividing by 60: 4 hours 30 minutes is 4.5 hours.
• Convert pounds to kilograms by dividing by 2.2046: 154 lb is about 69.9 kg.

Worked examples

1. 280 ml over 6 hours at 70 kg: 280 ÷ 6 = 46.7 ml an hour, and 46.7 ÷ 70 = 0.67 ml/kg/hr, inside the usual adult range.
2. 120 ml over 4 hours at 80 kg: 120 ÷ 4 = 30 ml an hour, and 30 ÷ 80 = 0.38 ml/kg/hr. That is below 0.5, which matters if it continues for 6 hours or more despite normal drinking.
3. 450 ml over 7 hours 30 minutes at 154 lb: the time is 7.5 hours and the weight about 69.9 kg, so 450 ÷ 7.5 = 60 ml an hour, and 60 ÷ 69.9 = 0.86 ml/kg/hr.

How to calculate 24-hour urine output

Add up every void over a full day. Start just after the first pee of the morning, measure everything from then on, and finish with the first pee of the next morning, so the period covers exactly 24 hours and no void is counted twice. Divide the total by 24 for the average hourly rate, or by your weight for ml/kg a day. Most adults pass 1,200 to 2,000 ml in 24 hours; the full table is in normal urine output per day.

What the result means for adults

• Under 0.5 ml/kg/hr: low. Common for a few hours after little to drink, or overnight. Under the KDIGO guideline, below 0.5 ml/kg/hr for 6 hours or more is one of the criteria for acute kidney injury; the stages are in normal urine output per hour, with a chart by weight.
• 0.5 to 1 ml/kg/hr: the usual adult range, about 35 to 70 ml an hour at 70 kg.
• Above 1 ml/kg/hr: normal after drinking a lot. Over a whole day, bladder guidelines call more than about 40 ml/kg in 24 hours polyuria, and kidney specialists often use more than 3 litres or 50 ml/kg a day.
• Under about 400 to 500 ml in 24 hours, roughly 20 ml an hour, is called oliguria.

These figures are for adults. Children's thresholds are different, so ask the child's care team about a child's output.

Getting an accurate number

• Count the time from the last void before the period started, not from the first void inside it, or that first void will include urine made before the clock started.
• Measure every void in a jug or container marked in ml. One missed void makes the rate look low. The options and their accuracy are in how to measure urine volume.
• Check the weight unit: entering pounds as kilograms makes the result look less than half as large as it is.
• In hospital, a urinary catheter with an hourly measuring bag gives the most accurate hourly readings, which is why intensive care measures output this way.

Sources: KDIGO Clinical Practice Guideline for Acute Kidney Injury, Kidney Int Suppl 2012;2:1-138; Al-Kazwini H, Simhadri PK, Normal and Abnormal Urine Output and Interpretation, StatPearls, updated May 2024.

This article is educational and does not provide medical advice, diagnosis or treatment.