Fluid Requirement Calculator
Calculate daily maintenance fluid requirements using the Holliday-Segar method.
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How to use this calculator
The Holliday-Segar method (1957) estimates a daily maintenance volume from body weight, derived from caloric expenditure data of roughly 100 mL of water per 100 kcal. It is applied in three weight bands: 100 mL/kg for the first 10 kg, 50 mL/kg for the next 10 kg and 20 mL/kg for every kg above 20. The hourly figure shown is the daily total divided by 24.
- 1
Enter the patient's body weight in kilograms.
- 2
The calculator applies the Holliday-Segar bands to that weight.
- 3
Read the daily total in mL/day and the same total divided by 24 in mL/hr.
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The tool has no inputs for fever, losses, kidney disease or other factors, so the result is the same for any person of that weight.
Frequently asked questions
What does the calculation actually do?
It splits the body weight into three bands, multiplies the kilograms in each band by a fixed millilitres-per-kilogram figure built into this tool, and adds the three pieces to get a daily volume. The first band is the lowest weights, the second the next block of kilograms, and the third every kilogram beyond that. It then divides the daily volume by 24 to display an hourly figure.
Where do the per-kilogram figures come from?
They are the published Holliday-Segar figures, 100 mL/kg/day for the first 10 kg, 50 mL/kg/day for the next 10 kg and 20 mL/kg/day for each kg beyond 20, as listed in the formula line above. The method was derived for hospitalised children, and the tool does not check it against any current guideline; use of any volume is for the prescriber or a pharmacist to confirm.
What weight units and values are accepted?
Weight is entered in kilograms. A weight of 0, which is also what a cleared box becomes, or a negative weight returns an error message rather than a result. The tool never substitutes a default weight. Decimals are accepted, and there is no upper limit on the weight entered.
Is the hourly figure the same as the 4-2-1 rule?
Not exactly. The tool shows the daily total divided by 24. The 4-2-1 rule (4 mL/kg/hr for the first 10 kg, 2 for the next 10, 1 per kg beyond) is a rounded hourly version; for 70 kg it gives 110 mL/hr against 104.2 here. Neither accounts for oral intake, the type of fluid or staging across the day, and the tool has no input for those.
Does it adjust for fever, losses, kidney or heart disease?
No. The only input is weight. There are no fields for temperature, vomiting, diarrhoea, drains, urine output, electrolytes, age group or medical conditions, so the result is the same for every person of a given weight.
Why is the result rounded?
The daily volume is shown to the nearest whole millilitre and the hourly figure to one decimal place. The hourly value is calculated from the unrounded daily total, so the two numbers can differ very slightly from a hand calculation that starts with the rounded daily figure.
Can this be used to order or give fluids?
No. It does arithmetic on one weight and is not a prescription or an order. Fluid orders come from the prescriber and local protocol.
Weight-banded daily fluid arithmetic — how the tool builds its numbers
Three weight bands, one running total
The calculator treats weight as a staircase. Kilograms in the lowest band are multiplied by the highest per-kilogram figure, the next block of kilograms by a smaller one, and any weight beyond that by the smallest. The three subtotals are added. Because the later bands apply only to the extra kilograms, the total rises steadily with weight but at a slower pace each time a band is passed. The constants are the published Holliday-Segar figures: 100, 50 and 20 mL per kg per day.
From daily total to an hourly figure
After the daily volume is found, the tool divides it by 24 and shows the answer as an hourly rate in millilitres. That is a straight division, nothing more: it assumes the volume is spread evenly over the day and ignores meals, drinks, medicines given in fluid and any planned changes in the rate. Weight must be entered in kilograms, and a zero or negative entry, including a cleared box, produces an error instead of a zero.
Four sample weights
The weights below were typed into the calculator and the outputs copied directly, so they illustrate how the arithmetic behaves across the bands. They are not recommendations for any person.
| Weight | Daily volume | Hourly figure |
|---|---|---|
| 8 kg | 800 mL/day | 33.3 mL/hr |
| 15 kg | 1250 mL/day | 52.1 mL/hr |
| 25 kg | 1600 mL/day | 66.7 mL/hr |
| 70 kg | 2500 mL/day | 104.2 mL/hr |
Reading the examples
Compare the 15 kg and 25 kg rows. The heavier person weighs 10 kg more, yet the daily total rises by only 350 mL, and the hourly figure by 14.6 mL, because those extra kilograms fall into the lower-rate bands. At 8 kg, only the first band applies, so the total is a simple multiple of the weight. The 70 kg row shows that the adult result is still driven mostly by the first two bands, with the remaining kilograms adding a smaller share.
What the tool leaves out
There is no input for age, temperature, ongoing losses, kidney or heart function, electrolytes or the fluid type, so two very different patients of the same weight receive the same number. This page is general information, not medical advice and not for clinical decisions, and it must not be used to decide a patient’s fluid prescription. Anyone checking a fluid order relies on their institution’s approved method and a second professional check.
Learn more from an authoritative source:
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →