A 1,000 mL IV fluid bag does not translate into a fixed amount of urine. Some fluid remains in the bloodstream and tissues, and urine output depends on kidney function, blood pressure, heart function, ongoing losses, and the reason fluids were given.

For most adults, a usual minimum target is:

Example: a 70 kg adult should generally produce at least 35 mL/hour, or around 280 mL over 8 hours, if adequately perfused and kidneys are functioning.

Do not expect all 1,000 mL to come out as urine immediately. Fluid balance should be assessed using urine output, vital signs, examination, weight, and blood tests, as recommended by the NICE IV-fluid guidance. A surgical text similarly notes that, without kidney dysfunction, urine output over 30 mL/hour is a rough sign that fluid replacement may be adequate - Pye's Surgical-Handicraft, Intravenous fluids.

If urine is less than 0.5 mL/kg/hour for several hours, or there is no urine for 6-8 hours, this needs prompt clinical assessment, especially if there is swelling, breathlessness, low blood pressure, kidney disease, or heart failure.