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Urine Output (mL/kg/h) and Fluid Balance

Urine output = urine volume ÷ weight ÷ hours (mL/kg/h). Below 0.5 mL/kg/h for ≥6 h meets the KDIGO AKI stage 1 criterion, for ≥12 h stage 2, and <0.3 mL/kg/h for ≥24 h or anuria ≥12 h stage 3. Net balance = intake − all output.

Urine volume (mL or L)
Collection period (h or min)
Weight (kg or lb)
Total intake over same period (optional) (mL or L)
Other output (drains, NG, stool) (optional) (mL or L)

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Interpretation

Result	Meaning
≥ 0.5	Adequate (adults)
< 0.5 for 6–12 h	KDIGO stage 1
< 0.5 for ≥ 12 h	KDIGO stage 2
< 0.3 for ≥ 24 h or anuria ≥ 12 h	KDIGO stage 3

Formula

UO (mL/kg/h) = urine volume (mL) ÷ weight (kg) ÷ hours. Net balance = intake − (urine + other output).

Clinical pearls

KDIGO criteria use actual body weight; in obesity this can overcall oliguria, and some clinicians use ideal weight.
Infants and young children normally produce more (≈ 1–2 mL/kg/h); < 1 mL/kg/h is commonly used as oliguria in infants.
Charted balances omit insensible losses (≈ 500–1000 mL/day in adults, more with fever or ventilation).

Examples

urine output 200 ml over 8 hours 70 kg uop 1.2 L in 24h weight 80kg, intake 2.5 L is a 60 kg patient with 150 mL urine in 6 hours oliguric?

FAQ

What is normal urine output in mL/kg/h?

At least 0.5 mL/kg/h in adults; persistently lower output for 6 hours or more meets the KDIGO AKI criterion.

How do you calculate urine output per kg per hour?

Divide the urine volume in mL by body weight in kg and by the number of hours collected. Example: 200 mL over 8 h in 70 kg = 0.36 mL/kg/h.

Evidence

Khwaja A. KDIGO clinical practice guidelines for acute kidney injury. Nephron Clin Pract 2012;120:c179–84.

Nephrology & Electrolytes · Reviewed 2026-10-14 · Methodology