Oral Rehydration Solution (ORS) Calculator — WHO Plans A, B and C
Work out how much oral rehydration solution (ORS) a child with diarrhea needs by weight and dehydration level, following WHO Plans A, B and C, plus the zinc dose.
How it works
Plan B: ORS (ml) in 4 hours = 75 × weight (kg) · Plan A: 50–100 ml after each loose stool under 2 years, 100–200 ml at 2–10 years · Plan C: 100 ml/kg IV (30 ml/kg then 70 ml/kg) · zinc 10 mg/day under 6 months, 20 mg/day from 6 months
The WHO manual “The treatment of diarrhoea” sorts children into three plans. Plan A (no dehydration) treats at home with extra fluids and ORS after every loose stool. Plan B (some dehydration: restless or irritable, sunken eyes, drinks eagerly, skin pinch goes back slowly) gives about 75 ml/kg of low-osmolarity ORS over 4 hours under observation, by spoon or cup, then reassesses. Plan C (severe dehydration: lethargic, unable to drink, skin pinch goes back very slowly) needs 100 ml/kg of intravenous fluid in hospital. Zinc for 10–14 days shortens the illness, and breastfeeding and feeding should continue.
Worked example
A child aged 12–23 months weighing 10 kg with some dehydration (Plan B): ORS = 75 × 10 = 750 ml in the first 4 hours, about 188 ml per hour or 47 ml every 15 minutes, given as 1 teaspoon (5 ml) every 1–2 minutes, plus zinc 20 mg a day for 10–14 days.
Sources: WHO (2005) The treatment of diarrhoea: a manual for physicians and other senior health workers · WHO — Diarrhoeal disease fact sheet
Frequently asked questions
How much oral rehydration solution should I give my child?
With some dehydration, the WHO recommends about 75 ml per kg of body weight over 4 hours — 750 ml for a 10 kg child. Without dehydration, give 50–100 ml after each loose stool under 2 years and 100–200 ml from 2 to 10 years.
What if my child vomits the ORS?
Wait 10 minutes, then continue more slowly, for example one spoonful every 2–3 minutes. Small, frequent amounts are usually kept down. Seek care if vomiting is repeated and the child cannot keep anything down.
What are the danger signs of severe dehydration?
Lethargy or unconsciousness, inability to drink or drinking poorly, very sunken eyes and a skin pinch that goes back very slowly (more than 2 seconds). These need emergency treatment with intravenous fluids.
Why is zinc given with ORS?
Zinc for 10–14 days (10 mg a day under 6 months, 20 mg a day from 6 months) reduces the length and severity of diarrhea and the chance of another episode in the next few months.
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This calculator gives general guidance and is not a diagnosis or medical advice. If you are worried about your child, or they seem unwell, contact your pediatrician, a health center or emergency services.