Baby · Health
Pediatric Medication Dose
Weight-based dose calculation for the common paediatric medications — paracetamol, ibuprofen, amoxicillin (standard and high-dose), ondansetron, cetirizine, diphenhydramine. Doses calibrated against the BNF for Children (BNFc 2024-2025) and AAP / Lexicomp paediatric standards.
Last reviewed 25 May 2026
Paediatric dose calculator
Weight-based medication dose (mg/kg)
Medication
Standard antipyretic / analgesic. Age ≥ 2 months and weight ≥ 4 kg (UK BNFc); from birth in some specialist contexts.
Units
kg
mo
Enter weight and age to calculate the dose.
Safety rules
- NEVER aspirin in under-16s with fever (Reye syndrome).
- NEVER ibuprofen under 3 months. Avoid in dehydration.
- NEVER codeine / dihydrocodeine / tramadol under 12.
- Use a dosing syringe — kitchen teaspoons are inaccurate.
- If unsure — call your GP, pharmacist, or NHS 111 / Poison Control.
Doses calibrated against the BNF for Children (BNFc 2024-2025) and AAP / Lexicomp paediatric drug references. This calculator is a CHECK, not a prescription — always verify against product label and clinician guidance.
What does this mean?
The most common cause of paediatric medication errors at home is the wrong dose for weight, usually too much. A few key safety rules: (1) use the oral syringe that comes with the bottle, not a kitchen spoon (teaspoons vary 2–7 mL); (2) check the strength (infant drops vs children’s suspension are different concentrations — dosing by mL is meaningless without the strength label); (3) respect the daily max (paracetamol 60 mg/kg/day; ibuprofen 30 mg/kg/day); (4) never aspirin in < 16 y with fever (Reye syndrome); ibuprofen NOT under 3 months and avoid in dehydration; never codeine/tramadol < 12 y; (5) if treating fever, the goal is comfort, not a target temperature (NICE NG143, AAP 2011 reaffirmed 2020) — don’t alternate antipyretics on a clock, treat symptoms.
How to use this calculator
Pick the medication, enter the child’s weight (kg or lb) and age in months. The calculator returns the per-dose milligram target, the frequency, the daily maximum, and the volume of suspension to draw up for common formulations. The values match the BNF for Children and AAP / Lexicomp paediatric references.
Why mg/kg instead of age bands?
Because children at the same age can vary by 50-100 % in weight. Product labels round to age bands for safety in self- administration, but the underlying evidence is mg per kilogram of body weight. A small 4-year-old (14 kg) needs less than a large 4-year-old (22 kg) of the same medication. For most over-the- counter doses the difference is small, but for prescription antibiotics, antiemetics, and sedatives it can be substantial.
Drugs included
- Paracetamol (acetaminophen) — 15 mg/kg/dose every 4-6 h. Max 60 mg/kg/day or 4 g/day. From 2 months / 4 kg (BNFc).
- Ibuprofen — 10 mg/kg/dose every 6-8 h. Max 30 mg/kg/day or 2.4 g/day. NOT under 3 months. Cautious in dehydration / asthma exacerbation / kidney issues.
- Amoxicillin (standard) — 15 mg/kg three times daily. For most ENT and respiratory infections.
- Amoxicillin (high-dose AOM) — 30 mg/kg three times daily (80-90 mg/kg/day). Per AAP CPG 2013 for acute otitis media in regions with pneumococcal resistance.
- Ondansetron — 0.15 mg/kg every 8 h. For paediatric gastroenteritis vomiting. From 6 months.
- Cetirizine — non-sedating antihistamine, fixed-dose by age band. Preferred over diphenhydramine from 12 months.
- Diphenhydramine (Benadryl) — first-generation antihistamine. NOT under 2 years (sedation, paradoxical excitation, respiratory depression). Less preferred where cetirizine is available.
Hard safety rules
- No aspirin under 16 with fever — Reye syndrome risk.
- No ibuprofen under 3 months / 5 kg — renal immaturity, NSAID risk.
- No codeine, dihydrocodeine, tramadol under 12 — variable CYP2D6 metabolism, respiratory depression deaths reported (EMA/FDA/MHRA 2013).
- Always a dosing syringe or supplied cup — household teaspoons range 2-7 mL.
- Keep a dosing diary when combining/alternating paracetamol and ibuprofen — accidental double-dosing of paracetamol is the leading paediatric overdose presentation.
- Under 2 months with fever ≥ 38 °C — straight to medical assessment, not antipyretic. Sepsis / meningitis / UTI more common at this age.
Limitations
- This is a sanity-check tool, not a prescribing tool. It does not account for medical conditions, concurrent medications, or organ-function impairment.
- Concentrations vary by country and formulation — the calculator covers common UK and US formulations; check your specific product label.
- For neonates (under 1 month), use specialist neonatal references; this calculator starts at 2 months for paracetamol and is age-restricted for other drugs.
- For unconscious / vomiting children, oral medication is contraindicated — seek medical care.
Sources
- BNF for Children 2024-2025. Royal Pharmaceutical Society / BMJ / NICE.
- American Academy of Pediatrics. Red Book 2024-2027.
- Sullivan JE, Farrar HC. Fever and Antipyretic Use in Children. AAP Clinical Report, Pediatrics 2011;127:580-7 (reaffirmed 2020).
- NICE NG143. Fever in under 5s: assessment and initial management. 2021.
- AAP. The Diagnosis and Management of Acute Otitis Media (Clinical Practice Guideline). Pediatrics 2013;131:e964-e999.
- Yin HS, et al. Liquid medication errors and dosing tools: a randomized controlled experiment. JAMA Pediatr 2014.
- EMA / MHRA. Codeine: restricted use in children. 2013.
Frequently asked questions
Is this a replacement for talking to a doctor or pharmacist?
No. It's a sanity check on the dose you've calculated from the bottle, or a quick cross-reference to bring to a phone call. The doses here are calibrated against the BNF for Children (the UK paediatric prescribing reference) and AAP / Lexicomp paediatric standards, but real prescribing accounts for the child's medical history, current medications, kidney/liver function, and condition severity. When in doubt, call your GP, pharmacist, NHS 111 (UK), Poison Control (US: 1-800-222-1222), or 999/911.
Why is age-based dosing on the bottle different from this?
Because product labels round to neat age-band doses (e.g. '3-6 years: 5 mL') for safety in self-administration. The actual evidence-based dose is mg/kg of body weight. A small 4-year-old (14 kg) needs less paracetamol than a large 4-year-old (22 kg); the bottle gives both the same dose for safety. Weight-based calculation is more accurate but requires knowing the exact weight. The calculator AGREES with bottle labels for average-weight children — it diverges only when your child is at the small or large end of the band.
Why never aspirin for children under 16?
Reye syndrome — a rare but devastating acute hepatic and cerebral oedema condition associated with aspirin given to children with viral infections (flu, varicella). Incidence dropped from ~600 US cases/year in the 1980s to fewer than 5/year today after public-health warnings. UK and US guidance: NO aspirin for ANY child under 16 with fever, headache, or flu-like illness, except for specific paediatric rheumatology / cardiac indications under specialist supervision.
Can I give paracetamol and ibuprofen at the same time?
Yes — they can be safely combined or alternated. NICE NG143 (Fever in under-5s, 2021) recommends not using both simultaneously as a routine, but allowing alternation if one alone isn't controlling distress. Many UK and US paediatricians advise: paracetamol every 6 hours and ibuprofen every 8 hours, offset by 2-3 hours, so the child has something working at all times. KEEP A DOSING DIARY — it's easy to lose track and accidentally double-dose paracetamol.
Why is ibuprofen banned under 3 months?
Renal immaturity. Under 3 months, the neonatal / young infant kidney has limited ability to handle NSAIDs and the risk of acute kidney injury rises sharply. Below 5 kg body weight ibuprofen is also not licensed. Paracetamol from 2 months / 4 kg is the antipyretic of choice in young infants. For under-2-month-olds with fever, the answer is medical assessment — not medication — because serious bacterial infection (sepsis, meningitis, UTI) is more common at this age.
What about teaspoons vs dosing syringes?
Always use a dosing syringe or the cup provided with the medication. Household 'teaspoons' vary from 2-7 mL; a 'tablespoon' from 12-20 mL. Dosing errors with kitchen utensils account for ~50,000 paediatric medication ER visits per year in the US (Yin 2010, JAMA Pediatrics). Pharmacy syringes are calibrated and free.
Why no codeine / dihydrocodeine / tramadol under 12?
Variable CYP2D6 metabolism. ~10 % of European-ancestry people and up to 30 % of some Middle Eastern populations are ultra-rapid metabolisers, converting codeine to morphine much faster than expected. Multiple paediatric deaths from respiratory depression after codeine for post-tonsillectomy pain led EMA / FDA / MHRA to contraindicate codeine in under-12s (2013) and avoid up to 18 in tonsillectomy / adenoidectomy patients. Dihydrocodeine and tramadol follow similar restrictions. Paracetamol + ibuprofen handle most paediatric pain; specialist opioid prescribing is rare and supervised.