Baby · Hydration
ORS Volume for Paediatric Dehydration
Weight-based oral rehydration solution dose for diarrhoea and vomiting in children — WHO 2006 / NICE CG84 / AAP. Plus how to tell mild from severe dehydration, what NOT to give, and when it's time for A&E.
Last reviewed 28 May 2026
ORS for paediatric dehydration
WHO/AAP oral rehydration volume
Units
kg
Dehydration severity
count
count
Enter weight to calculate ORS volume.
Educational tool only — not medical advice. WHO 2006 reduced-osmolarity ORS (Na 75 mEq/L, glucose 75 mmol/L, total osmolarity 245 mOsm/L) is the standard worldwide. Don’t use sports drinks, fruit juice, soda — too much sugar, wrong electrolytes. Don’t use plain water for diarrhoea — risks hyponatraemia. For severe dehydration, shock, or persistent vomiting unable to keep ORS down, seek IV care urgently.
What does this mean?
ORS exploits the sodium-glucose cotransport in the gut: as glucose moves into the cell, sodium — and with it water — follows. This pathway works even during severe diarrhoea, which is why ORS has saved an estimated tens of millions of children’s livessince its WHO introduction in the 1970s. Modern reduced-osmolarity ORS (WHO 2006, Na 75 / Glu 75 mmol/L) is gentler on the gut and reduces vomiting and stool output compared to the older 90 mmol/L formulation. Don’t substitute with juice, soda or sports drinks — they have too much sugar (pulls water INTO the gut, worsening diarrhoea) and wrong electrolyte ratios. Add zinc 10–20 mg/day for 10–14 days (WHO/UNICEF 2004): shortens diarrhoea by ~25 % and reduces recurrence over the following 2–3 months. Continue breastfeeding throughout. Re-feed normal diet within 24 hours — gut atrophy from starvation is the old mistake.
How much ORS does my child need?
Type your child’s weight into the calculator above, choose mild or moderate dehydration, and you’ll get the millilitres of ORS to give over the next 3-4 hours — plus the top-up volume for each subsequent watery stool or vomit.
- Mild dehydration: 50 mL/kg over 3-4 hours.
- Moderate dehydration: 100 mL/kg over 3-4 hours.
- Severe / shock: 999 / A&E — IV fluids first, ORS later.
- Ongoing losses: add 10 mL/kg ORS per watery stool, 2 mL/kg per vomit.
How do I tell how dehydrated my child is?
You’re looking for a pattern, not a single sign. Check several things together:
- Mild (3-5% body weight loss): a bit thirsty, slightly dry mouth, normal alertness, normal pulse, normal urine output (just slightly less).
- Moderate (5-10%): sunken eyes, very dry mouth, irritable or quiet, fewer pees / wet nappies than usual, sunken soft spot in babies, cool hands and feet, faster pulse.
- Severe (> 10% — emergency): very lethargic / hard to wake, deeply sunken eyes, no tears when crying, no wet nappy for 8+ hours (infant) or 12+ hours (older child), weak / fast pulse, mottled skin, very slow capillary refill (press fingernail, count seconds for colour to return — over 3 sec is slow).
The classic “pinch the skin and see how fast it flattens” test is a LATE sign and unreliable in well-nourished children — don’t rely on it.
How do I actually GIVE the ORS?
- Small, frequent sips. 5-10 mL every 1-2 minutes initially. Yes, that’s an annoying amount of work, but it’s the key — gulping a cup will trigger vomiting in a sick gut.
- Use a syringe / spoon / dropper if your child won’t accept a cup. Squirt to the side of the cheek so they have to swallow rather than choke.
- Chill the ORS — tastes much better cold.
- Freeze ORS into ice lollies — kids love them and they sip slowly.
- Flavoured ORS (blackcurrant Dioralyte, fruit Pedialyte) is genuinely more drinkable.
- If they vomit — wait 5-10 minutes, then restart with even smaller sips (2-3 mL every minute). Most kids manage even when they’ve been vomiting if you go small and slow.
- Don’t dilute the ORS — it changes the electrolyte balance.
What NOT to give a vomiting / diarrhoea child
- Sports drinks (Lucozade Sport, Powerade, Gatorade) — too little sodium, too much sugar. Can worsen osmotic diarrhoea.
- Fruit juice — too much sugar, no sodium.
- Cola / fizzy drinks / sweet tea — very high sugar; the “flat coke for tummy aches” folk remedy is wrong and harmful.
- Plain water alone for diarrhoea — risks dilutional hyponatraemia. Some water is fine but with ORS, not as a replacement.
- Loperamide (Imodium) in children — never. Slows the gut, increases toxic megacolon risk in bacterial dysentery.
- Diluted formula — prolongs diarrhoea per current evidence. Keep formula full-strength.
- The old “BRAT diet for days” (banana, rice, apple sauce, toast) — outdated. Introduce normal food within 4-6 hours of starting ORS.
Different scenarios — how the ORS approach plays out
Scenario 1: 18-month-old, 11 kg, 4 watery poos today, drinking a bit, fewer wet nappies
Mild-to-moderate dehydration. Start with 550 mL ORS (50 mL/kg) over 3-4 hours — about 140 mL/hour. Use ice lollies, syringe, or cup. Continue breastfeeding alongside. Add 10 mL/kg = 110 mL per additional watery stool. Reassess in 4 hours.
Scenario 2: 8-month-old, 8 kg, vomiting every 30 min for 4 hours, very sleepy
Possibly moderate-to-severe. Try 5 mL ORS every 1-2 min by syringe. If can’t hold any down OR very lethargic OR sunken fontanelle OR no wet nappy in 8 hours — A&E for IV fluids and possibly ondansetron.
Scenario 3: 6-week-old breastfed baby, watery stools 6× today, looking floppy
Baby under 6 months with significant diarrhoea = same-day GP / paediatric review regardless of dehydration severity. Continue breastfeeding, give 5 mL ORS between feeds. Don’t wait it out.
Scenario 4: 5-year-old, 18 kg, 1 episode vomit yesterday, no diarrhoea, drinking and weeing fine
Probably not dehydrated. Trial of plain fluids and a light bland meal. If diarrhoea kicks in, switch to ORS approach. If vomits come back > 2-3 times, switch to ORS.
Scenario 5: 3-year-old, 15 kg, 24 hours of diarrhoea, bloody stool today, fever 38.8 °C
Bloody stool + fever = same-day GP. Likely bacterial (Shigella, Salmonella, Campylobacter, E. coli). Stool sample requested. Antibiotics MAY or may not be needed depending on organism (E. coli O157: antibiotics avoided due to HUS risk). Continue ORS in meantime.
When does a child need IV fluids and A&E?
- Severe dehydration signs — very lethargic, hard to wake, sunken eyes, no tears, no urine in 8h (infant) / 12h (older), weak pulse, mottled, capillary refill > 3 sec.
- Persistent vomiting unable to keep ORS down for ≥ 4 hours despite tiny sips.
- Signs of shock (cold, mottled, very fast pulse, slow capillary refill).
- Bloody diarrhoea (dysentery) — antibiotic decision needed.
- High fever (≥ 38.5 °C in over-3-mo, ≥ 38 °C in under-3-mo) WITH diarrhoea.
- Severe localised abdominal pain (appendicitis, intussusception in differential).
- Diarrhoea > 14 days — persistent / chronic.
- Baby under 6 months with significant diarrhoea, regardless.
- You’re worried — trust your instincts.
Care guidance — the whole-family picture
- Continue normal feeding alongside ORS (breastmilk, formula, age-appropriate solids).
- No bland-diet weeks — introduce normal food within 4-6 hours of starting ORS. Banana, plain pasta, plain rice, toast, soup, yogurt all fine. Avoid VERY sugary or VERY fatty foods initially.
- Wash hands compulsively after every nappy change and before food prep. Norovirus and rotavirus spread on hands at terrifying efficiency. Soap and water beats hand sanitiser for these viruses.
- Separate towels for the sick child during illness.
- Disinfect toilet seats, taps, door handles daily during the illness and for 48 hours after the last episode.
- Keep them home from nursery / school until 48 hours after the last episode of diarrhoea or vomiting.
- Don’t share cutlery / cups with siblings during the illness.
- Zinc 10-20 mg/day for 10-14 days is reasonable (WHO).
- Probiotic Lactobacillus rhamnosus GG or Saccharomyces boulardii may shorten illness by ~1 day (modest evidence).
- Rotavirus vaccine for under-1s (UK NHS schedule at 8 + 12 weeks) cuts severe rotavirus diarrhoea by ~85%.
Limitations
- This calculator is a guide; actual dosing varies by clinical context.
- Severe dehydration and certain pathologies (severe malnutrition, intussusception, hypernatraemic dehydration) need specialist care — ORS alone isn’t enough.
- Educational only; persistent or worsening dehydration needs medical assessment.
Sources
- WHO / UNICEF. Joint Statement: Clinical Management of Acute Diarrhoea. 2006.
- WHO. Treatment of Diarrhoea: A manual for physicians and other senior health workers.
- King CK, et al. Managing acute gastroenteritis among children: oral rehydration, maintenance, and nutritional therapy. AAP Clinical Practice Guideline. Pediatrics 2003;111:e637.
- Guarino A, et al. ESPGHAN / ESPID evidence-based guidelines for the management of acute gastroenteritis in children in Europe. JPGN 2014;59:132-52.
- NICE CG84. Diarrhoea and vomiting caused by gastroenteritis in under 5s.
- Lazzerini M, Wanzira H. Oral zinc for treating diarrhoea in children. Cochrane Database Syst Rev 2016.
- Szajewska H, et al. Probiotics for the prevention and treatment of antibiotic-associated diarrhoea. ESPGHAN position paper.
- UK Health Security Agency. Health Protection in Schools and Other Childcare Facilities.
Recommended for this calculator
Frequently asked questions
What is ORS and how does it work?
ORS stands for Oral Rehydration Solution — a specific mix of glucose, sodium, potassium, chloride and citrate. The WHO 2006 reduced-osmolarity formula (Na 75 mEq/L, glucose 75 mmol/L, total 245 mOsm/L) is the global standard. The trick is the GLUCOSE-SODIUM CO-TRANSPORT mechanism in the small intestine — glucose enables sodium absorption even when diarrhoea has knocked out other sodium-transport routes; water follows the sodium. ORS has saved tens of millions of children's lives since its introduction (UNICEF) — one of the most cost-effective public health interventions ever.
How do I tell if my child is dehydrated?
MILD (3-5% body weight lost): slightly thirsty, slightly dry mouth, normal alertness, normal pulse. MODERATE (5-10%): sunken eyes, very dry mouth, irritable or quiet, fewer wet nappies/pees, sunken fontanelle in babies, cool extremities, faster pulse. SEVERE (>10%): very lethargic, hard to wake, eyes very sunken, no tears when crying, no wet nappy for 8+ hours (infant) / 12+ hours (child), weak pulse, mottled skin, very slow capillary refill — this is shock, call 999. The 'pinch test' — pinched skin slow to flatten — is a late sign and unreliable in well-nourished children.
What does my child weigh? How much ORS do I give?
MILD dehydration: 50 mL/kg over 3-4 hours. MODERATE: 100 mL/kg over 3-4 hours. Use the calculator above for the exact number. Practical example: a 10 kg toddler with moderate dehydration needs 1000 mL of ORS over 3-4 hours — about 250-300 mL/hour, given as 5-10 mL sips every 1-2 minutes. Yes, that sounds like a lot — but small, very frequent sips are the key. Babies often tolerate a syringe or spoon better than a cup.
How much ORS for each watery stool or vomit?
On top of the rehydration phase: 10 mL/kg of ORS for each watery stool, 2 mL/kg for each vomit. For a 12 kg child with 3 watery stools and 2 vomits since the last top-up: (3 × 120) + (2 × 24) = 408 mL extra over the next hour or two. Continue throughout the illness. This is the 'replacing ongoing losses' phase and runs alongside normal feeding.
Where do I buy ORS?
Pharmacies, supermarkets, online — brands vary by country. UK: Dioralyte (sachets dissolved in water); Electrolade; Pedialyte (US, also some UK stockists). US: Pedialyte (ready-to-drink or powder), CeraLyte, Enfalyte. Globally: WHO-formula sachets. Avoid 'plus' formulations with extra glucose unless specifically advised — the WHO ratio is what makes it work. Generic pharmacy brands work the same. Buy a few sachets to have at home — diarrhoea always strikes at 11pm on a Sunday.
Can I give my child sports drinks like Lucozade or Powerade?
No, not for diarrhoea or vomiting. Sports drinks have too LITTLE sodium (around 18-20 mEq/L vs 75 mEq/L needed) and too MUCH sugar — the high sugar can actually pull more water into the gut and worsen diarrhoea (osmotic diarrhoea). They're designed for sweaty athletes, not sick children. Same problem with fruit juice (way too much sugar, no sodium). Cola, soft drinks, and sweetened tea are even worse — actively harmful.
Can I make ORS at home in an emergency?
Yes, as a stop-gap if you can't get to a pharmacy. WHO emergency homemade recipe: 6 LEVEL teaspoons of sugar + 1 LEVEL teaspoon of salt + 1 LITRE of clean (boiled and cooled) water. Stir until dissolved. Taste it — it should taste like tears, not the sea. If it tastes saltier than tears, throw it out and remake; too much salt is dangerous (hypernatraemia). Less precise than commercial ORS (no potassium, no citrate buffer), so swap to commercial as soon as available.
What if my child won't drink the ORS — it tastes salty?
It does taste odd. Tricks that help: (1) chill it well — much more palatable cold. (2) freeze ORS into ice lollies — kids love these and they sip slowly. (3) give via syringe / spoon / dropper — 5 mL every 1-2 minutes; many kids who refuse a cup accept this. (4) flavoured ORS (blackcurrant Dioralyte, fruit-flavoured Pedialyte) is genuinely better-tolerated. (5) reward and praise — make it a game. (6) for breastfed babies, alternate ORS sips with breastfeeds. Don't dilute ORS — that changes the electrolyte balance.
Should I keep breastfeeding when my baby has diarrhoea?
YES — keep breastfeeding throughout. Breastmilk is well-tolerated and isn't an alternative to ORS but works alongside it. Offer ORS between feeds initially; reduce ORS once feeding is back to normal. For formula-fed babies, keep formula at full strength (don't dilute) — current evidence is that diluting formula prolongs diarrhoea. Older babies and toddlers: ORS first to rehydrate; then introduce normal food early (within 4-6 hours of starting ORS, not the old 'BRAT diet for days').
When does my child need to go to A&E for diarrhoea / vomiting?
Same-day GP / A&E if: severe dehydration signs (very sleepy, no wet nappy in 8+ hours infant / 12+ hours older child, sunken eyes, weak pulse, cold extremities, mottled skin); persistent vomiting unable to keep ORS down for 4+ hours; BLOODY diarrhoea (dysentery — bacterial); high fever (≥ 38.5 °C in over-3-month, ≥ 38 °C in under-3-month) WITH diarrhoea; diarrhoea lasting more than 14 days; baby under 6 months with significant diarrhoea; abdominal pain that's severe / persistent / localised; signs of shock (mottled, very fast pulse, slow capillary refill, confused). Trust your instincts — if you're worried, get them seen.
Does my child need antibiotics for diarrhoea?
Usually no. About 80% of acute gastroenteritis in children is VIRAL (rotavirus, norovirus, adenovirus) — antibiotics do nothing. Bacterial causes (Salmonella, Shigella, Campylobacter, E. coli) usually clear on their own too and antibiotics can occasionally worsen things (E. coli O157:H7 + antibiotics → higher haemolytic uraemic syndrome risk). Antibiotics ARE needed for: severe Shigella (high fever, bloody dysentery), C. difficile, prolonged Giardia, Cholera, and travel diarrhoea in some contexts. Your GP will decide based on travel history, stool sample, severity.
What about anti-diarrhoea medicines like loperamide?
NEVER use loperamide (Imodium) in children under 12 with acute gastroenteritis. Loperamide slows the gut so the infection has more time to do damage, increasing toxic megacolon risk in bacterial dysentery. UK and US guidelines explicit: don't use in children. Adults can use it for traveller's diarrhoea but not if blood / fever / under 3 days into illness. Ondansetron (anti-vomit) is sometimes used in A&E to break a vomiting cycle that's preventing ORS intake — single dose, weight-based — but isn't a home medicine.
Does zinc supplementation actually help diarrhoea?
Yes — WHO/UNICEF recommend zinc 10-20 mg/day for 10-14 days for diarrhoea in children under 5, especially in low-resource settings. Reduces diarrhoea duration by 25-30% and reduces the chance of further episodes over the next 2-3 months (Cochrane 2016). In high-resource UK / US / EU settings, zinc is less commonly prescribed routinely but ESPGHAN 2014 supports it for prolonged or recurrent diarrhoea. Over-the-counter as 10 mg dispersible tablets in many countries. Take with food to reduce nausea.
What about probiotics for diarrhoea?
Modest evidence. Specific strains — Lactobacillus rhamnosus GG and Saccharomyces boulardii — have the most data for shortening rotavirus diarrhoea by about 1 day in children (Cochrane 2020). ESPGHAN 2014 cautiously supports their use as an adjunct, not a replacement for ORS. Won't hurt; cost / convenience matters. NOT routinely recommended in NICE CG84 because the absolute benefit is small. ORS, continued feeding, and good handwashing are the high-yield interventions.
When can my child go back to nursery / school after diarrhoea?
UK Health Protection guidance: 48 hours after the LAST episode of diarrhoea or vomiting. Same in most US districts. Doesn't matter how well they otherwise feel — the 48-hour rule is about contagion. For some specific causes (Cryptosporidium, E. coli O157, typhoid) longer exclusion applies and may need negative stool samples. Norovirus and rotavirus are especially infectious. Wash hands compulsively for the family in the week after — virus shed in stool for 1-2 weeks.
Diarrhoea in pregnancy — same approach?
Largely yes. Hydration is the priority. ORS is safe in pregnancy. Loperamide is generally avoided. Probiotics safe. The thing to be alert to in pregnancy: dehydration can trigger Braxton-Hicks / preterm contractions, so don't tough it out — drink ORS proactively. Persistent diarrhoea > 48 hours in pregnancy warrants GP review (rule out IBD flare, infection, listeria — especially after eating risk foods).
Can adults use the same ORS?
Yes — adult oral rehydration dose is roughly 1.5-2 L of ORS over the first hour or two for moderate dehydration, then 200-400 mL after each loose stool / vomit. Adult sports performance-style 'electrolyte' drinks are usually too low in sodium for actual gastroenteritis; use real ORS sachets. Sip frequently rather than gulp.
How does this relate to other calculators on BumpBites?
Companion: /calculators/pediatric-dose for the ondansetron or other meds; /calculators/baby-percentile for tracking growth recovery; /calculators/newborn-diaper-output for the hydration check; /calculators/baby-cough if vomiting is from coughing (post-tussive); /calculators/hand-foot-mouth if oral ulcers stopping drinking; /calculators/water-intake for maternal hydration.