Pediatric Weight-Based Dosing Calculator

Pediatric medicines are dosed by body weight because children vary so widely in size. This calculator multiplies weight by a mg/kg figure, applies a per-dose ceiling so heavier children are not overdosed, and shows both the single and daily doses.

How it works

The core arithmetic is:

per-dose mg  = weight_kg * mg_per_kg_per_dose   (capped at the max per dose)
daily total  = per-dose mg * doses_per_day

Selecting a preset drug loads its typical mg/kg, frequency, and absolute per-dose maximum. If the weight-based figure would exceed that maximum (which happens for larger children), the tool caps the dose and flags it so you can re-check. The custom option lets you enter parameters for any drug.

Example

A 14 kg child given paracetamol at 15 mg/kg per dose receives 14 × 15 = 210 mg per dose, well under the 1000 mg ceiling. At four doses a day that is 840 mg/day, within the 75 mg/kg/day daily limit.

Why the per-dose ceiling matters

The mg/kg dosing model is designed for the typical child, but it does not scale linearly for all body weights. For many drugs, a large child given the full mg/kg calculation would receive more than the safe adult dose — an unnecessary and potentially harmful amount. The per-dose ceiling prevents this: once the weight-based calculation reaches the ceiling, the dose is capped regardless of weight, and the tool flags this so you can note that the child is being given the adult maximum dose rather than a weight-scaled one.

For example, ibuprofen at 10 mg/kg for a 60 kg teenager calculates to 600 mg per dose. If the ceiling is 400 mg, the cap activates and the child receives 400 mg — the standard adult maximum for a single dose. Without the ceiling check, the weight calculation alone could produce an overdose for heavier children.

Practical guidance: formulation concentration

Knowing the dose in milligrams is only the first step. Dispensing a liquid medicine requires dividing the milligram dose by the concentration in the available formulation. Pediatric paracetamol suspensions commonly come in 120 mg/5 mL or 250 mg/5 mL concentrations. For a 210 mg dose:

• 120 mg/5 mL → 8.75 mL needed
• 250 mg/5 mL → 4.2 mL needed

Using the wrong concentration bottle while calculating from the right milligram dose is one of the most common pediatric medication errors. Always check the label of the bottle you are dispensing from, not just the nominal drug name, and document the concentration explicitly.

Age-band considerations

Body weight is the primary dosing determinant, but age also matters. Some drugs have lower mg/kg limits for infants under six months, different ceiling values for neonates, or are not recommended before a certain age at all. The tool’s presets reflect typical values for children; for very young infants, always verify the current drug reference for your age band rather than relying on a general mg/kg figure.

Notes

Presets are orientation values, not a substitute for a current pediatric formulary. Always verify against the exact formulation strength (many pediatric liquids come in several concentrations), the child’s age band, and a second clinician. This is an educational aid that runs entirely in your browser.