How does the WHO Plan B dose work?

The WHO treatment Plan B for some (mild to moderate) dehydration gives approximately 75 mL of ORS per kilogram of body weight over the first four hours. The calculator multiplies weight by 75 and divides the total over four hours to give an hourly target, offered in frequent small sips.

How is the NICE approach different?

NICE estimates a fluid deficit of 50 mL/kg for clinical dehydration and replaces it over four hours, given on top of normal maintenance fluids. This calculator shows the deficit volume and, when maintenance is included, adds the Holliday-Segar maintenance requirement so you see the full target.

What is the Holliday-Segar maintenance rule?

Daily maintenance fluid is 100 mL/kg for the first 10 kg, plus 50 mL/kg for the next 10 kg, plus 20 mL/kg for each kilogram above 20 kg. The four-hour share is one sixth of that daily figure, which the NICE-plus-maintenance option adds to the deficit.

When is oral rehydration not appropriate?

Oral rehydration is unsuitable for severe dehydration or shock, persistent vomiting that prevents intake, ileus, or reduced consciousness, all of which need intravenous fluids and urgent assessment. ORS is for mild to moderate dehydration in a child who can drink.

Is this calculator a prescription?

No. It reproduces published WHO and NICE volume rules for education and bedside cross-checking. Actual fluid management depends on ongoing losses, clinical reassessment, and the responsible clinician's judgement, and should follow local paediatric guidance.

What is the Oral Rehydration Solution Dosing Calculator?

Computes the oral rehydration solution volume to give over four hours using WHO (75 mL/kg for some dehydration) and NICE (50 mL/kg deficit plus maintenance) protocols, from a child's weight and dehydration grade. Runs in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Oral Rehydration Solution Dosing Calculator

Name: Oral Rehydration Solution Dosing Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Oral rehydration solution (ORS) replaces water and electrolytes lost through diarrhoea and is the first-line treatment for mild to moderate dehydration in children. The volume given is weight-based, and the two most widely used schemes are the WHO Plan B and the NICE deficit-plus-maintenance approach.

How it works

The WHO Plan B for some dehydration uses a single weight rule over four hours:

WHO volume (4 h) = 75 mL/kg x weight

The NICE approach replaces an estimated deficit and, optionally, adds maintenance:

deficit (4 h)    = 50 mL/kg x weight
maintenance/day  = 100 mL/kg (first 10 kg)
                 + 50 mL/kg (next 10 kg)
                 + 20 mL/kg (over 20 kg)
4 h maintenance  = maintenance/day / 6

Each total is divided across four hours and given as frequent small sips to maximise absorption and reduce vomiting.

Worked example

For a child weighing 15 kg with assessed mild-to-moderate dehydration:

WHO Plan B: 75 mL/kg × 15 kg = 1,125 mL over 4 hours, which is approximately 280 mL per hour — offered as frequent small sips, not a large bolus.

NICE deficit approach (with maintenance):

Deficit: 50 mL/kg × 15 kg = 750 mL
Daily maintenance: (100 × 10) + (50 × 5) = 1,250 mL/day
4-hour share of maintenance: 1,250 / 6 ≈ 208 mL
Total 4-hour target: 750 + 208 = 958 mL, roughly 240 mL per hour

The two protocols give different totals for the same child. The WHO Plan B is slightly higher; the NICE deficit-only approach is lower; NICE-plus-maintenance sits between. Which protocol your clinical setting follows depends on local paediatric guidance — this calculator lets you compare them side by side.

Why small sips matter

Rapid ORS administration increases the risk of vomiting, which reduces net fluid intake. The strategy of giving frequent small volumes — a few teaspoons every minute or two for very young children — maximises absorption across the gut wall and minimises the reflex to vomit. If a child vomits, wait 5–10 minutes and resume at a slower rate; a single vomit episode does not mean ORS has failed.

WHO ORS composition

Standard WHO/UNICEF low-osmolarity ORS contains (per litre of water): sodium 75 mmol, chloride 65 mmol, glucose 75 mmol, potassium 20 mmol, citrate 10 mmol — total osmolarity 245 mOsm/L. The reduced-osmolarity formulation replaced the earlier high-osmolarity version after evidence showed it reduces the volume of stool output and the rate of IV therapy in children with diarrhoea.

Notes and cautions

ORS is for the child who can drink and has mild to moderate dehydration. Severe dehydration, shock, persistent vomiting, ileus, or reduced consciousness require intravenous fluids and urgent assessment instead. Ongoing stool and vomit losses must be replaced in addition to the volumes here, and the child should be reassessed regularly. This calculator reproduces published WHO and NICE volume rules for education and cross-checking only; final fluid management follows local paediatric guidance and the responsible clinician’s judgement.