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General information only, not medical advice. Measuring urine output for a patient is a clinical task carried out under a clinician’s orders and the facility’s protocols; if you are caring for someone and are unsure, ask the responsible nurse or physician.
Short answer: urine output is measured by collecting all urine passed over a known time, reading the volume in millilitres (mL), and recording it with the time. Where a weight-based figure is needed, divide the volume by body weight in kilograms and by the hours covered, giving mL/kg/h. The KDIGO acute kidney injury guideline uses less than 0.5 mL/kg/h for 6 hours as one of its definitions of acute kidney injury.
This page is for nursing and support staff, students and caregivers who need to understand how output is collected and what the number is compared against. It covers the whole workflow rather than one device; for individual devices see the urine hat (specimen collector), the urimeter, the urinary drainage bag and the bedpan.
What you need
The equipment depends on how the patient passes urine. The US Food and Drug Administration groups urine collection devices under one regulation, 21 CFR 876.5250 (“Urine collector and accessories”), which describes a device intended to collect urine, made up of tubing, a suitable receptacle, connectors and mechanical supports. It names two kinds.
| Kind of collector (21 CFR 876.5250) | Examples named in the regulation |
|---|---|
| Connected to an indwelling catheter | Urinary drainage collection kit; closed urine drainage system and drainage bag |
| Not connected to an indwelling catheter | Corrugated rubber sheath; pediatric urine collector; leg bag for external use; urosheath-type incontinence device; paste-on device |
Whichever route is used, you also need a way to read volume in mL (a graduated chamber or graduated container), a clock, and the patient’s chart or fluid balance record. The CDC guideline for preventing catheter-associated urinary tract infection (CAUTI) says to empty a collecting bag regularly using a separate, clean collecting container for each patient, so a dedicated graduated container per patient belongs on the list. See types of catheter bags for the bag formats themselves and the CAUTI prevention bundle for the infection-prevention side.
Steps
These are general steps for recording output from a collection device or drainage bag that is already in place. Follow the facility protocol and the device manufacturer’s instructions for use, which take precedence over this summary.
- Note the start time. Output is only meaningful over a stated period, so record when the previous reading or emptying took place.
- Collect all urine for the period. Use the patient’s own collection device or drainage bag, not a shared container.
- Read the volume in mL from the graduated markings on the chamber, bag or container, then record it.
- Empty into a separate, clean, graduated container kept for that patient only when the bag is emptied, as the CDC guideline directs.
- Record the time, the volume (mL) and who measured it on the output chart or fluid balance record.
- Convert to a rate if asked to. Rate (mL/h) is volume divided by hours; weight-based rate (mL/kg/h) divides that again by body weight in kg.
Reading the number: mL/kg/h and the KDIGO thresholds
The KDIGO Clinical Practice Guideline for Acute Kidney Injury (Kidney International Supplements, 2012) is the standard reference that ties a measured output to a time and a body weight. Its recommendation 2.1.1 defines acute kidney injury (AKI) by any one of a serum creatinine rise or urine volume of less than 0.5 ml/kg/h for 6 hours. Its staging table then uses urine output as follows.
| AKI stage (KDIGO 2012) | Urine output criterion |
|---|---|
| Stage 1 | Less than 0.5 mL/kg/h for 6 to 12 hours |
| Stage 2 | Less than 0.5 mL/kg/h for 12 hours or more |
| Stage 3 | Less than 0.3 mL/kg/h for 24 hours or more, or anuria for 12 hours or more |
Recommendation 2.2.3 advises testing patients at increased risk of AKI with measurements of serum creatinine and urine output, and individualizing how often and for how long to monitor according to patient risk and clinical course. KDIGO does not give a single universal charting interval.
Worked example (arithmetic illustration only)
A patient weighs 70 kg and 210 mL of urine is collected over 6 hours. Per hour that is 210 ÷ 6 = 35 mL/h. Per kilogram, 35 ÷ 70 = 0.5 mL/kg/h. This example only shows how the units combine; deciding what a result means for a particular patient is a clinician’s task. The same arithmetic applies to the other thresholds above, using the patient’s actual weight and the actual hours covered.
What can go wrong
- Missing time stamps. A volume without the start and end time cannot be converted to a rate.
- Urine not collected. Anything passed outside the collection device is absent from the total, so the recorded figure understates output.
- Shared containers. Using one container for several patients conflicts with the CDC recommendation to use a separate, clean container for each patient when emptying bags.
- Wrong unit or weight. Mixing mL with litres, or using a weight in pounds where kilograms are required, changes the rate by a large factor.
When to get professional help
Ask the responsible nurse or physician what a reading means for a particular patient, and how to record a reading if you are unsure or the collection device is blocked, leaking or disconnected. Do not adjust fluids or treatment based on a calculated rate yourself. In an emergency, follow local emergency procedures.
FAQ
How do you measure urine output?
Collect all urine passed over a known period, read the volume in mL from a graduated device, and record the volume with the time. The weight-based rate is volume divided by body weight in kg and by the hours covered.
What is the formula for urine output in mL/kg/h?
mL/kg/h = volume (mL) ÷ body weight (kg) ÷ hours. For example, 210 mL over 6 hours for a 70 kg patient is 0.5 mL/kg/h.
What urine output counts as low in the KDIGO guideline?
KDIGO 2012 defines AKI by urine volume under 0.5 mL/kg/h for 6 hours, and stages it by duration and by a lower cut-off of 0.3 mL/kg/h for 24 hours or anuria for 12 hours. These are classification criteria for clinicians, not a self-diagnosis tool.
Sources
- KDIGO Clinical Practice Guideline for Acute Kidney Injury, Kidney International Supplements 2012;2(1): kdigo.org guideline PDF (checked 2026-11-04).
- CDC / HICPAC, Guideline for Prevention of Catheter-associated Urinary Tract Infections 2009, summary of recommendations: cdc.gov summary (page dated 2024-03-25, checked 2026-11-04).
- US FDA, 21 CFR 876.5250 Urine collector and accessories: law.cornell.edu/cfr/text/21/876.5250 (checked 2026-11-04).
Related equipment category: diagnostic and monitoring equipment.
