Pediatric Dehydration Fluid Calculator

Overview

The Pediatric Dehydration Fluid Calculator takes a child's weight and estimated degree of dehydration and works out the daily maintenance fluid requirement (Holliday-Segar), the fluid deficit already lost, and the oral rehydration solution (ORS) volume recommended by the WHO and the American Academy of Pediatrics — along with the hourly and every-five-minutes amounts to actually give. When a child is listless from gastroenteritis, the hardest question is how much to give and how fast; this calculator answers both in concrete millilitres based on body weight. If the estimated dehydration is 10% or more, if the child vomits everything back, or if they are lethargic, the calculator replaces the dosing figures with an emergency-department notice.

Formula

1) Maintenance fluid (Holliday-Segar, mL/day)
First 10 kg: 100 mL/kg · 10–20 kg: 50 mL/kg · above 20 kg: 20 mL/kg

2) Fluid deficit (mL) = weight (kg) × dehydration (%) × 10

3) ORS replacement — WHO / AAP oral rehydration therapy
Mild dehydration (3–5%): 50 mL/kg over 4 hours
Moderate dehydration (6–9%): 100 mL/kg over 4 hours
Under 3%: no set volume — replace ongoing losses only
10% or more (severe): not a candidate for oral replacement → IV fluids

4) Ongoing losses
10 mL/kg per diarrheal stool (max 240 mL) · 2 mL/kg per episode of vomiting

5) Rate
Hourly volume = total replacement ÷ replacement window (4 hours by default)
Amount every 5 minutes = hourly volume ÷ 12

e.g., a 12 kg child with moderate (8%) dehydration:
Maintenance = 10×100 + 2×50 = 1,100 mL/day
Deficit = 12 × 8 × 10 = 960 mL
ORS = 100 × 12 = 1,200 mL over 4 hours → 300 mL/hour → 25 mL every 5 minutes

How to Use

1. 1Enter the child's weight in kilograms — the current weight while ill.
2. 2Pick the degree of dehydration to auto-fill a representative percentage, or type the percentage directly if you know the weight lost since before the illness (that is more accurate).
3. 3Select the child's current state. Persistent vomiting or lethargy triggers an emergency notice instead of dosing figures.
4. 4Leave the replacement window at 4 hours (the WHO/AAP standard) unless you have a reason to change it.
5. 5Enter the number of diarrheal stools and vomits you expect during the window so ongoing losses are added.
6. 6Read off the total volume plus the hourly and every-five-minutes amounts, and give them with a spoon or oral syringe.

Examples

Background

The Holliday-Segar method behind the maintenance figure was published in Pediatrics in 1957 and has been the standard for pediatric fluid therapy ever since; the 100/50/20 mL/kg bands come from the observation that water requirement tracks energy expenditure rather than weight linearly. The deficit formula multiplies by 10 because one kilogram of body fluid is 1,000 mL, so each 1% of body weight lost equals 10 mL per kilogram. The 50 mL/kg (mild) and 100 mL/kg (moderate) volumes given over four hours are the oral rehydration therapy regimen shared by the WHO and the AAP; in acute gastroenteritis, ORT is as effective as intravenous fluids while reducing admissions and complications, which is why it is first-line. After four hours the child is reassessed, the same volume is repeated if signs persist, and 10 mL/kg is added for each further stool. The solution itself matters: reduced-osmolarity ORS (roughly 60–75 mmol/L sodium, 75–90 mmol/L glucose) is what these volumes assume, whereas sports drinks and fruit juices carry too much sugar and too little sodium and can drive osmotic diarrhea that worsens the dehydration.

Tips

• ✔The most accurate dehydration percentage comes from comparing pre-illness weight with current weight — dig up any measurement from the past two weeks.
• ✔Giving a full cup at once almost always provokes vomiting. Start with 5–10 mL every 5 minutes and build up; pacing is what makes ORT work.
• ✔If the child vomits, wait about 10 minutes and restart with a smaller volume rather than abandoning oral replacement.
• ✔Continue breastfeeding alongside ORS, and do not dilute formula — give it at normal strength.
• ✔Resume a normal diet promptly once rehydration is done; prolonged fasting delays gut recovery. Only fatty foods and sugary drinks need avoiding.
• ✔Log urine output and alertness every four hours so you can judge improvement and describe it accurately at the clinic.

FAQ