Paediatric Dose Calculator

Before dispensing or administering any paediatric dose, verify each of these five elements:

1. Correct weight: Has the child been weighed today (or recently)? Is the weight recorded in kilograms? Estimated weights are acceptable only in emergencies — always weigh the child as soon as feasible.
2. Correct dose per kg: Does the mg/kg dose match the formulary recommendation for this drug, this indication, and this age group? Higher or lower doses may apply to different infections or severity levels.
3. Dose within range: Is the calculated dose below the maximum single dose and below the maximum daily dose? Does it fall within the expected range for the child’s age?
4. Correct formulation: Is the concentration on the label the same concentration used in the calculation? Are you dispensing the correct product (suspension vs. drops vs. tablets)?
5. Measurable volume: Can the dose be practically measured with the available device (oral syringe, measuring cup)? Rounding to the nearest 0.1 mL (syringe) or 0.5 mL (cup) is acceptable for most drugs.

Tenfold (10×) dose errors are one of the most dangerous and common types of paediatric medication errors. They typically occur due to decimal point misplacement, unit confusion (mg vs. mcg), or calculation errors when converting between concentrations.

Prevention strategies include: always using a leading zero before a decimal point (write 0.5 mg, not .5 mg), never using a trailing zero after a decimal point (write 5 mg, not 5.0 mg), using standardised concentration labels, double-checking calculations with a second person for all high-risk medications, and using electronic prescribing systems with built-in dose-range checking wherever available.

A practical sanity check: if the calculated volume seems unusually large or small for the child’s age, recalculate. A neonate requiring 10 mL of a suspension or an older child requiring 0.02 mL of anything should trigger a pause and recheck.

Certain drug classes carry elevated risk of harm from dosing errors in children and should always be independently double-checked before administration:

• Opioids: Narrow therapeutic index, respiratory depression risk. Weight-based dosing is essential. Morphine, fentanyl, and codeine have age-specific contraindications.
• Insulin: Unit-based dosing with potentially fatal hypoglycaemia from overdose. Use insulin-specific syringes only. Verify units vs. mL.
• Anticonvulsants: Loading doses of phenytoin, phenobarbital, and levetiracetam are weight-based and given IV with cardiac monitoring. Calculation errors can cause cardiovascular collapse or inadequate seizure control.
• Chemotherapy: BSA-based dosing (not weight-based) for most agents. Errors are catastrophic. Protocol-driven verification is mandatory.
• Electrolytes (IV potassium, calcium): Concentration and rate errors can cause fatal arrhythmias. Always verify mEq dose, concentration, and infusion rate independently.
• Digoxin: Mcg/kg dosing with a very narrow therapeutic window. Tenfold errors between mcg and mg are classic and potentially fatal.

Calculated doses are rarely perfectly round numbers. Appropriate rounding depends on the drug’s therapeutic index and the available measuring device.

• Oral liquids (syringe): Round to the nearest 0.1 mL for volumes < 5 mL. Round to the nearest 0.5 mL for volumes ≥ 5 mL. Oral syringes are preferred over household teaspoons for accuracy.
• Tablets/capsules: Round to the nearest available tablet fraction. Half-tablets are acceptable for scored tablets. Quarter-tablets are unreliable — use liquid formulations instead.
• IV medications: Round to the nearest 0.1 mL for syringe-drawn doses. For infusions, round concentration-adjusted rates to practical pump settings.
• Narrow therapeutic index drugs: Do not round. Use exact volumes and verify with a second calculator or pharmacist.

General principle: rounding should never change the dose by more than 10% from the calculated value. If it does, choose a different formulation or concentration.

This is one of the most frequent sources of paediatric dosing errors. Some references list doses as mg/kg/dose (per administration), while others list mg/kg/day (total daily dose to be divided across multiple administrations). Confusing the two leads to either underdosing (if a per-day dose is given per administration without dividing) or overdosing (if a per-dose amount is multiplied as though it were per-day).

Example: Amoxicillin 75 mg/kg/day divided TDS = 25 mg/kg/dose three times daily. Misreading 75 mg/kg as per-dose gives a threefold overdose. Always verify whether the reference source quotes per-dose or per-day figures, and document the calculation clearly.

Age-based weight estimates (e.g., APLS formula: weight = 2 × (age + 4)) are intended for emergency resuscitation only and have wide confidence intervals — up to ±30% from actual weight. Using an estimated weight for routine drug dosing introduces unnecessary and preventable error.

Every child should be weighed on admission and periodically during hospitalisation. The weight must be in kilograms — weighing in pounds and converting introduces additional calculation steps and opportunities for error. Electronic prescribing systems should pull the documented weight automatically. If a child cannot be weighed (e.g., critical care, immobilisation), use a Broselow tape or the best available estimate and document the method used.

Many paediatric drugs come in multiple concentrations. Paracetamol is a classic example: infant drops (100 mg/mL), children’s suspension (120 mg/5 mL = 24 mg/mL), and adult suspension (250 mg/5 mL = 50 mg/mL). If the pharmacist dispenses one concentration but the prescriber calculated the volume based on another, the actual dose delivered can be dramatically wrong.

Prevention: always write the concentration on the prescription alongside the volume (e.g., “7.5 mL of paracetamol 120 mg/5 mL suspension”), verify the product label at the point of dispensing, and educate parents about which product they have at home. Automatic electronic dose calculators should be linked to the specific product, not just the drug name.

A 50 kg adolescent prescribed paracetamol at 15 mg/kg calculates to 750 mg per dose. The adult maximum single dose is 1,000 mg — so 750 mg is safe. But a 80 kg teenager at 15 mg/kg calculates to 1,200 mg — exceeding the maximum. Without a dose cap, weight-based dosing in large children leads to supratherapeutic doses.

Every weight-based prescription should include an explicit maximum dose. This calculator allows you to enter a maximum single dose that automatically caps the result. In practice, many institutions transition to adult fixed dosing once a child exceeds a threshold weight (typically 40–50 kg) or age (12–16 years, depending on the drug).

Many drugs have different mg/kg doses depending on the indication. Amoxicillin is 25 mg/kg/dose TDS for standard infections but 40–45 mg/kg/dose BD for acute otitis media. Ibuprofen is 5–10 mg/kg for analgesia but different protocols exist for PDA closure in neonates (which uses a different drug form entirely). Prednisolone is 1 mg/kg for mild asthma exacerbations but 2 mg/kg for severe presentations.

A generic “dose of amoxicillin” is clinically meaningless without the indication. Always specify the indication when looking up paediatric doses, and ensure the mg/kg value entered into this calculator matches the intended clinical use.