Pediatric Fluid Replacement Calculator
Estimates the hourly oral or IV fluid replacement rate for a dehydrated child based on weight, dehydration severity, ongoing losses, and the desired replacement timeframe. Use it when managing gastroenteritis or other causes of childhood dehydration.
Last updated: October 2026
Hourly Fluid Rate
150 ml/hr
Formula below · 3 sources (CDC, medicalguidelines.msf.org, professionals.wrha.mb.ca) · Updated Oct 2026
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About this calculator
For a child with mild dehydration, the standard oral rehydration plan is about 50 mL of oral rehydration solution (ORS) per kg of body weight over roughly 4 hours, and about 100 mL/kg for moderate dehydration; a 12 kg child with mild dehydration therefore needs about 600 mL, or 150 mL an hour over 4 hours. This calculator estimates that deficit from weight and severity, adds an allowance for ongoing vomiting or diarrhea, and divides by the hours you choose.
How the estimate works
Hourly rate = (weight × deficit + weight × ongoing-loss allowance) ÷ hours. The deficit is 50 mL/kg for mild (3 to 5%) and 100 mL/kg for moderate (6 to 9%) dehydration. Ongoing losses add 10 mL/kg for mild or 20 mL/kg for significant losses; guidelines size this more precisely at about 10 mL/kg for each watery stool. Severe dehydration returns an emergency message instead of a rate.
Giving the fluid
Use a commercial or WHO-formula ORS, not plain water, juice, soda or sports drinks, which have the wrong balance of salt and sugar. Give small amounts often, such as a teaspoon (5 mL) every minute or two with a syringe or spoon for a young child, and increase as it is kept down. Continue breastfeeding, and restart the usual diet once the child is rehydrated.
When to get help now
Severe dehydration is an emergency that needs IV fluids in hospital. Seek care immediately for lethargy or unusual sleepiness, no urine for many hours, sunken eyes with no tears, persistent vomiting that prevents drinking, or blood in the stool. This calculator supports a plan from a clinician; it does not replace an examination.
| Dehydration | Typical signs | ORS for the deficit | Example: 12 kg child |
|---|---|---|---|
| Mild (3–5%) | Thirst, slightly dry mouth, less urine | About 50 mL/kg over about 4 h | 600 mL (150 mL/h over 4 h) |
| Moderate (6–9%) | Sunken eyes, dry mouth, few tears, little urine | About 100 mL/kg over about 4 h | 1,200 mL (300 mL/h over 4 h) |
| Ongoing diarrhea | — | About 10 mL/kg per watery stool, on top | 120 mL per stool |
| Severe (10% or more) | Lethargy, very little or no urine, signs of shock | Emergency: IV fluids in hospital | Call 911 or go to the ED |
How to use
Enter the child's weight in kg, choose the dehydration severity your clinician assessed, the time frame for replacement and the level of ongoing losses. The default, a 12 kg child with mild dehydration replaced over 4 hours with no ongoing losses, gives (12 × 50) ÷ 4 = 150 mL per hour of ORS. A 12 kg child with moderate dehydration and significant ongoing losses over 8 hours gives (1,200 + 240) ÷ 8 = 180 mL per hour. Severe dehydration returns an emergency message.
Frequently asked questions
How much oral rehydration solution does a dehydrated child need?
About 50 mL per kg of body weight over roughly 4 hours for mild dehydration and about 100 mL per kg for moderate dehydration, plus replacement of ongoing losses, about 10 mL per kg for each watery stool. A 10 kg toddler with mild dehydration needs about 500 mL over 4 hours.
What fluids should I use for rehydration?
Use an oral rehydration solution made for the purpose, sold in pharmacies or prepared from WHO-formula sachets exactly as directed. Plain water, juice, soda and sports drinks are not suitable for rehydration because their sugar and salt content is wrong for replacing diarrheal losses.
When does a child need IV fluids instead?
When dehydration is severe, when the child is lethargic or shows signs of shock, or when vomiting prevents keeping any fluid down despite small, frequent sips. These children need emergency care. Mild to moderate dehydration without these signs can usually be treated with ORS.
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Sources & references
- CDC, MMWR Recommendations and Reports (2003) — Managing acute gastroenteritis among children: oral rehydration, maintenance, and nutritional therapy
- MSF Clinical Guidelines — Appendix 14: WHO rehydration plans in patients with diarrhoea
- Winnipeg Regional Health Authority — Clinical practice guideline: Infant and child dehydration due to diarrhea
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