From mg/kg to the exact millilitres of the bottle in front of you. 30 medicines, rounded to what a syringe can actually measure, with the daily caps applied and a schedule written plainly enough to hand to the family.
Drug interactions · Pregnancy & breastfeeding · Clinical calculators · Versión en español
Pick the medicine, enter the weight and the age. If you do not know the weight, tick the box and we will estimate it from the age — but we will say so on every result, because a dose based on an estimated weight is not the same as one based on a measured weight.
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Brands and strengths differ by country, so we do not guess yours. Read the strength off the pack and type it here — that is what a pharmacist does anyway, and it is the only number that makes the millilitres right.
For guidance. Check the dose against the product information before dispensing. The final clinical decision rests with the paediatrician.
The point of getting the dose right is knowing when the right answer is not a syrup. Tick what you can see; the age comes from the calculation above.
None of them produces a visible error: they produce a confident, wrong number.
The commonest and the costliest. «Amoxicillin 40-90 mg/kg/day» split into 3 doses is 13-30 mg/kg each time. Reading it as if it were per dose triples the amount. And the other way round: reading «paracetamol 15 mg/kg/dose» as a daily total leaves the child on a quarter of the dose, with the fever not coming down.
The calculator always shows both figures — per dose and per day — and how many doses fit in 24 h.
Paediatric ibuprofen exists at 20 mg/mL and at 40 mg/mL. The same 5 mL is 100 mg or 200 mg depending on the bottle. Paracetamol is worse: 120 mg/5 mL, 160 mg/5 mL and 250 mg/5 mL are all on the shelf, and Spanish drops are 100 mg/mL — four times the infant suspension for the same volume.
That is exactly why this page asks you for the strength instead of assuming a product.
The age tables on the leaflet assume an average weight. Two four-year-olds can be 6 kg apart, and in a per-kilo dose that is 40 % either way. Age tells you whether the medicine is licensed, not how much to give.
Weight rules; age checks the licence and estimates the weight only when there is none.
«4.73 mL» is not a schedule: it is an unfinished calculation. Whoever has to carry it out at eleven at night rounds it however they can, and sometimes rounds up.
It rounds to the syringe's real step, and always down: overshooting has consequences, being a tenth short does not.
The per-kilo dose grows with weight; the cap does not. A 55 kg adolescent on 15 mg/kg of paracetamol would be 825 mg per dose and 3,300 mg a day — over the 3 g cap. Past a certain weight the rule that governs is the absolute maximum.
The result says when the cap comes into play, and shows the maximum for that child, not the adult one.
It does not bring the fever down further and it multiplies the mistakes made at home: two medicines, two clocks and two different syringes at four in the morning. It is not recommended as routine. And the target is not the number on the thermometer either: a child at 38.5 °C who is playing and drinking needs nothing.
One clear schedule gets followed; two alternating ones get followed badly.
All 30 medicines in the catalogue, with the schedule and the minimum licensed age. Tap any of them to work it out above with your patient's weight.
| Medicine | Indication | Dose | Frequency | Minimum age |
|---|---|---|---|---|
| Paracetamol (acetaminophen) | Antipyretic / analgesic | 10–15 mg/kg/dose | every 4-6 h | No limit |
| Ibuprofen | Antipyretic / anti-inflammatory | 5–10 mg/kg/dose | every 6-8 h | 3 months |
| Amoxicillin | Beta-lactam antibiotic | 40–90 mg/kg/day | every 8-12 h | No limit |
| Amoxicillin/clavulanate (8:1) | Broad-spectrum antibiotic | 40–80 mg/kg/day (amoxicillin) | every 8 h | 2 months |
| Azithromycin | Macrolide antibiotic | 10 mg/kg on day 1 + 5 mg/kg on days 2-5 | every 24 h for 3-5 days | 6 months |
| Cefuroxime axetil | Second-generation cephalosporin | 20–30 mg/kg/day | every 12 h | 3 months |
| Inhaled salbutamol (albuterol) | Beta-2 agonist bronchodilator | 2–10 puffs (100 µg/puff) | every 4-6 h through a spacer | No limit |
| Oral prednisolone | Systemic corticosteroid (asthma, allergy) | 1–2 mg/kg/day | every 24 h (morning) for 3-5 days | 6 months |
| Dexchlorpheniramine | First-generation H1 antihistamine | 0.15–0.2 mg/kg/day | every 6-8 h | 2 years |
| Cetirizine | Second-generation H1 antihistamine | 0.25 mg/kg/dose | every 12-24 h | 2 years |
| Ondansetron | Antiemetic (5-HT3) | 0.15 mg/kg/dose | every 8 h (occasional use) | 6 months |
| Montelukast | Leukotriene receptor antagonist (asthma, allergy) | fixed dose by age | every 24 h (at night) | 6 months |
| Vitamin D3 (cholecalciferol) | Supplement / rickets prophylaxis | 400 IU/day (under 1 year) | every 24 h | No limit |
| Oral rehydration solution (ORS) | Rehydration in gastroenteritis | 50–100 mL/kg over 4 h | small, frequent sips | No limit |
| Metamizole (dipyrone) | Analgesic / antipyretic | 10–20 mg/kg/dose | every 6-8 h | 3 months |
| Cefadroxil | First-generation cephalosporin | 30 mg/kg/day | every 12 h | No limit |
| Clarithromycin | Macrolide antibiotic | 15 mg/kg/day | every 12 h | 6 months |
| Cefixime | Third-generation cephalosporin | 8 mg/kg/day | every 24 h | 6 months |
| Fosfomycin trometamol | Antibiotic (uncomplicated UTI) | fixed dose | single dose (2 g in ages 6-12) | 6 years |
| Inhaled budesonide | Asthma (maintenance) | fixed dose by age | every 12 h | 6 months |
| Dexamethasone (croup) | Acute laryngitis / croup | 0.15–0.6 mg/kg/dose | single dose | 3 months |
| Loratadine | Second-generation antihistamine | fixed dose by weight | every 24 h | 2 years |
| Desloratadine | Second-generation antihistamine | fixed dose by age | every 24 h | 12 months |
| Omeprazole | Gastro-oesophageal reflux | 0.7–1.4 mg/kg/day | every 24 h | 12 months |
| Racecadotril | Acute diarrhoea (adjunct) | 1.5 mg/kg/dose | every 8 h | 3 months |
| Macrogol (polyethylene glycol) | Constipation | fixed dose by age | every 24 h | 6 months |
| Oral iron (ferrous sulfate) | Iron deficiency / anaemia | 3–6 mg/kg/day | every 24 h | No limit |
| Mebendazole | Threadworms / pinworms | fixed dose | single dose, repeat after 2 weeks | 12 months |
| Permethrin 1.5% (topical) | Head lice | topical | apply, and repeat after 7-10 days | 2 years |
| Melatonin | Difficulty falling asleep | fixed dose | 30-60 min before bedtime | 2 years |
The APLS formulas used in paediatric emergency care when there are no scales. They are an estimate: a child on the 3rd centile and one on the 97th at the same age are several kilos apart, and in a per-kilo dose that shows.
| Age | Estimated weight | Formula |
|---|
Use it to orient yourself, never to dispense without weighing. If the pharmacy has scales, weighing the child takes thirty seconds and removes the largest source of error in the whole calculation.
The calculation engine is a pure layer with no DOM access
(/calculos/dosis-pediatricas.js) and it is covered by automated tests that
run on every change. The figures come from Pediamécum (Spanish Association of
Paediatrics), the AEMPS product information and SEPEAP guidelines.
The usual schedule is 10-15 mg/kg per dose every 4-6 hours, without exceeding 60 mg/kg a day. For 15 kg that is 150-225 mg per dose. The millilitres depend entirely on your bottle: at 120 mg/5 mL that is about 6-9 mL, at 250 mg/5 mL about 3-4.5 mL. Read the strength off the pack.
By weight, whenever it is known. Age does two different jobs: checking that the medicine is licensed at that age, and estimating the weight when there are no scales. A dose based on an estimated weight is a guide — weigh the child and check it again.
In mg/kg/dose the figure is what you give each time. In mg/kg/day it is the day's total, which then has to be split between the doses. Confusing them multiplies or divides the dose by the number of doses — it is the commonest paediatric dosing error there is.
Divide the milligrams by the strength. 200 mg of amoxicillin at 250 mg/5 mL (that is 50 mg/mL) is 4 mL. The classic mistake is using the strength of a different presentation of the same medicine: paediatric ibuprofen exists at 20 mg/mL and 40 mg/mL, and the same volume is twice the dose.
Because the products are not the same in every country and the millilitres come from dividing by the strength. Spanish paracetamol drops are 100 mg/mL; Calpol Infant is 120 mg/5 mL, which is 24 mg/mL. Showing you a Spanish product's strength would put a volume on screen four times larger than the right one, without any error appearing. The strength on the pack in front of you is the only one that is certainly correct.
Fever in an infant under 3 months is an urgent referral, with no antipyretic first that could mask the picture. Also: a rash that does not blanch under pressure, signs of dehydration, vomiting that prevents oral rehydration, marked lethargy or fever lasting more than 48-72 h with no source. There is a checker above, in Dispense or refer?.
Not as routine. It does not bring the fever down further and it multiplies dosing mistakes at home, because it means keeping two clocks. And the target is not the number on the thermometer but how the child is.
Because a dosing syringe measures in steps of 0.1 mL (or 0.25-0.5 mL on the larger ones) and «4.73 mL» is not something anyone can do. It rounds down deliberately: in children, being a tenth short has no consequences and overshooting can.
Look it up in the purple field of the calculator: the entry is generated with AI and comes flagged with an AI badge. That entry is not reviewed by hand, so check it against the product information before dispensing. The fixed catalogue of 30 medicines is reviewed.
No. It is a calculation aid for the counter and for the family. Prescribing and the clinical decision belong to the paediatrician, and the product information for the specific medicine always overrides any general schedule.
The dosing rules (mg/kg, intervals and caps) are international and come from these sources. What is not international is the packaging: strengths, brands and licensed ages differ by country, which is why this page asks for the strength of your product and why you should confirm anything you act on with your own national medicines agency.