Pediatric Medication Dosage Calculator
Calculates the correct medication dose for a child from their weight and the prescribed dose per kilogram. Used by parents, nurses, and caregivers to prepare accurate doses of common pediatric medicines — always verify against the maximum-dose cap.
Last updated: May 2026
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About this calculator
Most pediatric medications are dosed on a per-kilogram basis to account for differences in body size, organ maturity, and drug metabolism between children. The core formula is: total_dose_mg = weight_kg × dose_per_kg_mg. Variables: weight (child's actual weight in kg, ideally measured the same day for young children whose weight changes rapidly), dose_per_kg (the medication's recommended dose in mg/kg, from the prescriber, drug formulary, or pediatric reference). For liquid medications, an additional step is needed: volume_mL = total_dose_mg / concentration_mg_per_mL. Edge cases: this calculator computes weight-based dose only and does not automatically enforce maximum dose caps — most pediatric drugs have a maximum single dose (typically the adult dose) that must not be exceeded regardless of weight. Always cross-check the calculated dose against the maximum stated in the product information or BNF for Children. Common pediatric drugs and their typical doses: paracetamol/acetaminophen 15 mg/kg q4–6h (max 60–75 mg/kg/day; max single dose ~1 g in older children); ibuprofen 10 mg/kg q6–8h (max 40 mg/kg/day; max single dose 400 mg); amoxicillin 25–50 mg/kg/day in 3 divided doses. Neonates and young infants (<3 months) often have different per-kg doses due to immature hepatic and renal clearance and should be dosed only with explicit neonatal guidance. Drugs with narrow therapeutic index (digoxin, chemotherapy, opioids, methotrexate) require BSA-based dosing or specialist input rather than simple weight-based math. Always use a measured/weighed weight in kg — estimated weights are a common source of error.
How to use
Example 1: A 20 kg child prescribed ibuprofen at 10 mg/kg per dose. Step 1: total dose = 20 × 10 = 200 mg per dose. Step 2: liquid form is 100 mg/5 mL suspension (= 20 mg/mL). Step 3: volume = 200 / 20 = 10 mL per dose. Verify: ibuprofen pediatric max single dose is 400 mg; 200 mg is well within that. Daily total at q6h = 4 × 200 = 800 mg, also within the 40 mg/kg/day cap (20 × 40 = 800 mg). Example 2: A 12 kg toddler prescribed paracetamol at 15 mg/kg q4–6h. Step 1: per-dose = 12 × 15 = 180 mg. Step 2: suspension is 250 mg/5 mL (= 50 mg/mL). Step 3: volume = 180 / 50 = 3.6 mL per dose. Verify: max single dose is ~500 mg in toddlers; 180 mg is well under. Max daily (4 doses) = 720 mg, well under the 60 mg/kg/day cap (12 × 60 = 720 mg) — exactly at limit; do not exceed 4 doses in 24 hours.
Frequently asked questions
Why are pediatric medication doses calculated per kilogram of body weight?
Children are not simply small adults — their body composition (more water, less fat), organ maturity (immature renal and hepatic function in infants), and metabolic rates differ significantly from adults and change rapidly with age. Dosing by weight ensures that the amount of drug relative to body size remains within a therapeutic range that is effective without being toxic. A flat dose appropriate for a 30 kg child could dangerously overdose a 10 kg toddler or undertreat a larger adolescent. Weight-based dosing is the international standard for pediatric pharmacotherapy and is supported by published reference works (BNF for Children, Lexicomp Pediatric, Harriet Lane Handbook). Some drugs (especially chemotherapy and certain cardiac drugs) instead use body surface area (BSA in m²) for more precise scaling.
How do I convert a pediatric weight-based dose from mg to mL for a liquid medicine?
Once you have calculated the total dose in milligrams (total_dose = weight × dose_per_kg), divide it by the concentration of the liquid formulation: volume_mL = total_dose_mg ÷ concentration_mg_per_mL. The concentration is printed on the medicine label, often expressed as 'mg per 5 mL'. For example, if the concentration is 250 mg/5 mL, the equivalent is 50 mg/mL, and a 200 mg dose requires 200 ÷ 50 = 4 mL. Always use a calibrated oral syringe (provided with the medicine or from the pharmacy), not a household teaspoon — kitchen spoons vary from 3 to 8 mL, introducing dangerous errors. Many pediatric formulations come in multiple strengths (e.g., infant vs children's paracetamol); always confirm which concentration you have before calculating volume.
What is the maximum dose I should give a child even if the weight-based calculation is higher?
Most pediatric drug guidelines specify a maximum single dose and a maximum daily dose that typically mirrors the standard adult dose, regardless of weight. This cap exists because drug clearance, receptor sensitivity, and toxicity thresholds eventually plateau and do not continue to scale linearly with weight, especially in adolescents approaching adult size. For example, ibuprofen is typically capped at 400 mg per dose (max 1.2 g/day) for children even if the weight-based calculation exceeds that; paracetamol is capped at about 1 g per dose for school-age children (max 4 g/day). Always cross-check your calculated dose against the maximum listed in the product information, pediatric formulary (BNF for Children in the UK), or by consulting a pharmacist or prescriber. Exceeding the cap risks hepatotoxicity (paracetamol), gastric bleeding (NSAIDs), or other organ-specific toxicities.
What are common mistakes when calculating pediatric medication doses?
Using estimated rather than measured weight introduces dosing errors of 10–30%, dangerous for narrow-therapeutic-index drugs. Confusing mg/kg with mg/kg/day (single dose vs total daily dose split across multiple doses) leads to either underdosing or massive overdosing. Forgetting to divide the daily dose by the number of doses per day for divided-dose regimens (e.g., 25 mg/kg/day in 3 divided doses = 8.3 mg/kg per dose). Using the wrong concentration when multiple strengths exist (infant vs children's drops are commonly different concentrations). Failing to check maximum dose caps when the weight-based calculation exceeds the adult dose. Using household teaspoons or tablespoons instead of calibrated oral syringes (spoons vary 3–8 mL). Calculating dose for the wrong child (especially in households with multiple children). Not converting weight from lbs to kg (1 lb = 0.4536 kg) when using metric-dosed guidelines. Finally, using over-the-counter combination products (e.g., cold medicines containing multiple actives) without summing the individual ingredient doses across all products.
When should I NOT use a simple weight-based pediatric dose calculator?
Neonates (under 1 month) and premature infants need specialist neonatal dosing — many drugs are dosed differently or contraindicated due to immature liver/kidney function and pharmacokinetics. Drugs with narrow therapeutic index (digoxin, lithium, warfarin, aminoglycosides, opioids, methotrexate, chemotherapy) need specialist supervision, often with therapeutic drug monitoring (blood levels). Drugs dosed by body surface area (chemotherapy, some cardiac medications) require the BSA calculator, not weight-based math. Obese children (BMI ≥95th percentile) may need adjusted dosing for certain drugs to avoid overdose based on fat mass; consult a pediatric clinical pharmacist. Children with renal or hepatic impairment need dose reductions or extended intervals — not a simple per-kg figure. Drugs given as fixed-dose pediatric formulations (e.g., asthma inhalers) don't use per-kg math. Combination over-the-counter medications can lead to double-dosing if the per-component dose isn't tracked. For any prescription medication, dose calculations should be verified by a pharmacist or physician; over-the-counter doses should match the age-band on the package label as a fail-safe check.