ORS and dehydration fluid calculator (WHO plans B and C)

ORS volume for some dehydration and IV Ringer’s lactate volumes for severe dehydration in children.

What this calculator is for

Diarrhoea is still a leading cause of child admissions in Pakistan, especially in summer. This calculator gives the WHO rehydration volumes for children by weight: oral rehydration salts (ORS) for some dehydration (Plan B) and IV Ringer's lactate for severe dehydration (Plan C).

Assess dehydration first

Severe (two or more): lethargic or unconscious, sunken eyes, not able to drink or drinking poorly, skin pinch goes back very slowly (2 seconds or more).
Some (two or more): restless or irritable, sunken eyes, drinks eagerly and thirsty, skin pinch goes back slowly.
No dehydration: not enough signs for either.

The WHO plans

Plan A (no dehydration, home): extra fluid and ORS after each loose stool, 50–100 mL under 2 years and 100–200 mL from 2 to 10 years, plus zinc and continued feeding.
Plan B (some): 75 mL/kg of ORS over 4 hours, then reassess.
Plan C (severe): 100 mL/kg of Ringer's lactate. Under 12 months: 30 mL/kg in 1 hour, then 70 mL/kg over 5 hours. 12 months or older: 30 mL/kg in 30 minutes, then 70 mL/kg over 2.5 hours. Repeat the first portion once if the radial pulse is still weak.

Worked example

A 10 kg, 18-month-old child with some dehydration: 750 mL of ORS over 4 hours, about 190 mL per hour, given by cup or spoon a little every minute or two. If the child vomits, wait 10 minutes and then continue more slowly.

Pitfalls

Use low-osmolarity ORS and mix it with exactly the volume of clean water printed on the sachet. Too concentrated ORS causes hypernatraemia.
Give zinc for 10–14 days and keep breastfeeding throughout.
Severely malnourished children must not receive these plans; they need the WHO malnutrition protocol and ReSoMal.
Reassess every 1–2 hours. A child who cannot drink in Plan B can take ORS by nasogastric tube.
Look for bloody stools, high fever and other causes of shock such as sepsis.

See diarrhoea and dehydration in children, ORS, zinc, Ringer's lactate and sepsis in children.

Frequently asked questions

How much ORS for a child with some dehydration?

75 mL/kg over 4 hours (WHO Plan B). For a 10 kg child that is 750 mL, about 190 mL per hour, given in small frequent sips.

What is WHO Plan C?

IV Ringer's lactate 100 mL/kg for severe dehydration: 30 mL/kg first (1 hour under 12 months, 30 minutes from 12 months), then 70 mL/kg (over 5 hours or 2.5 hours).

What zinc dose is given with ORS?

WHO recommends 10 mg daily under 6 months and 20 mg daily from 6 months, for 10–14 days.

Can severely malnourished children follow Plan B or C?

No. They are at high risk of fluid overload and need the WHO severe malnutrition protocol, including ReSoMal instead of standard ORS.

A calculator supports, but does not replace, clinical judgement. Check results before acting on them.