Maintenance IV Fluid (4-2-1) Calculator
Find hourly and daily maintenance fluids with the 4-2-1 rule.
Result
How it is calculated
The tool uses the tiered 4-2-1 rule on body weight W in kg, giving mL per hour. For W ≤ 10: rate = 4 × W. For 10 < W ≤ 20: rate = 40 + 2 × (W − 10). Above 20 kg: rate = 60 + 1 × (W − 20). The daily volume is the unrounded hourly rate × 24. Both numbers are rounded to whole millilitres, so the daily figure can differ slightly from 24 times the displayed hourly figure. Decimal weights such as 3.5 kg work. Only a weight above zero and up to 650 kg gives a result; zero, negative or heavier values show nothing. The rule is for maintenance only and it does not account for fever, losses, deficits or a patient's condition. Local protocols and fluid types differ, so the result is a starting estimate, not an order.
Worked example
Weight 32 kg. First 10 kg at 4 mL/h: 10 × 4 = 40 mL/h. Next 10 kg at 2 mL/h: 10 × 2 = 20 mL/h. Remaining 12 kg at 1 mL/h: 12 × 1 = 12 mL/h. Hourly total: 40 + 20 + 12 = 72 mL/h. Daily volume: 72 × 24 = 1,728 mL/day. The tool displays 72 mL/h and 1,728 mL/day.
Common mistakes
- Entering weight in pounds. A 70 lb child typed as 70 gets 110 mL/h instead of the 72 mL/h that belongs to roughly 32 kg.
- Multiplying the whole weight by 4 or by 1. The rates apply to tiers, so 32 kg is 40 + 20 + 12 mL/h, not 32 × 1 or 32 × 4.
- Treating the output as a total for the whole day when reading the first line. The headline figure is per hour. The daily volume is the second result.
- Entering an implausible body weight. Anything above 650 kg shows no result, but a typo within range, such as 500 kg, still returns 540 mL/h with no warning.
- Using the figure for resuscitation or replacement of losses. The 4-2-1 rule covers maintenance needs only.
About this calculator
The Holliday-Segar 4-2-1 rule, published by Malcolm Holliday and William Segar in 1957, estimates the hourly maintenance intravenous fluid rate a patient needs based purely on body weight: 4 mL/kg/hr for the first 10 kg of weight, 2 mL/kg/hr for the next 10 kg, and 1 mL/kg/hr for every kilogram above 20. It was derived from the observation that metabolic rate, and therefore fluid and calorie turnover, scales with body weight in a predictable, tiered way rather than linearly across the whole weight range.
Pediatricians, nurses, and anesthesiologists use the 4-2-1 rule constantly to set IV drip rates for patients who aren’t drinking enough on their own, whether during surgery, in the NICU or PICU, or on a general hospital ward, since it gives a fast bedside estimate without needing lab values or complex nomograms. It remains the standard teaching formula in medical and nursing education for maintenance fluids, distinct from resuscitation or replacement fluid calculations, which use different rules entirely.
This calculator takes a patient’s body weight and applies the 4-2-1 rule to return both the hourly maintenance fluid rate and the total daily volume.
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