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Pediatric Urine Output (mL/kg/h) Calculator

Q: How do I measure output in a child in nappies?

Weigh the dry nappy, then the wet one; the difference in grams is the millilitres of urine (subtract stool if obvious). Record the time between changes.

Q: Does high output matter?

Yes — over 4–6 mL/kg/h suggests polyuria: excess fluids, diuretics, hyperglycaemia, diabetes insipidus or recovery-phase AKI.

Urine output in mL/kg/hour for infants and children from measured volume, weight and hours — compared with the normal thresholds (≥ 1 mL/kg/h child, ≥ 2 infant), oliguria and AKI criteria, expected daily output and wet-nappy equivalents.

Weight

Urine volume measured

Over how many hours

Age group

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How it works

Urine output (mL/kg/h) = volume ÷ weight ÷ hours; normal: neonate/infant ≥ 2, child ≥ 1, adolescent/adult ≥ 0.5 mL/kg/h; KDIGO AKI: < 0.5 mL/kg/h for ≥ 6 h (stage 1), ≥ 12 h (stage 2), < 0.3 for ≥ 24 h (stage 3)

Urine output is the simplest bedside measure of a child’s kidney perfusion and hydration, but raw millilitres mean nothing without weight and time: 180 mL is generous for a 5 kg baby over eight hours and worrying for a 40 kg ten-year-old. Expressing it per kilogram per hour lets a single threshold apply — about 1 mL/kg/h for children, 2 for infants, whose kidneys concentrate urine poorly, and 0.5 for adolescents and adults. Falling output is an early sign of dehydration, shock or acute kidney injury, and the KDIGO staging uses sustained low output alongside creatinine to grade AKI. Weighing nappies (1 g ≈ 1 mL) makes measurement possible without a catheter; a well infant produces six or more wet nappies a day.

Worked example

A 12 kg toddler passes 180 mL in 8 hours: 1.88 mL/kg/h — adequate against the 1 mL/kg/h child threshold, projecting to about 540 mL a day, roughly nine wet nappies. At 60 mL in 8 hours (0.63 mL/kg/h) the output would be reduced and warrant reassessment.

Frequently asked questions

How do I measure output in a child in nappies?

Weigh the dry nappy, then the wet one; the difference in grams is the millilitres of urine (subtract stool if obvious). Record the time between changes.

Does high output matter?

Yes — over 4–6 mL/kg/h suggests polyuria: excess fluids, diuretics, hyperglycaemia, diabetes insipidus or recovery-phase AKI.

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