Child Dosage Calculator | Pediatric Dose Estimator

Enter child and medicine details

Large screens use 3 columns, smaller screens 2, and mobile 1.

Age (years)

Additional months

Weight

Height

Adult dose reference (mg)

Prescribed mg/kg/dose

Prescribed mg/kg/day

Prescribed mg/m²/dose

Doses per day

Liquid strength (mg)

Per liquid volume (mL)

Tablet strength (mg)

Maximum single dose (mg)

Maximum daily dose (mg/day)

Example data table

Age	Weight	Height	Adult Dose	mg/kg/dose	Doses/Day	Liquid Strength	Estimated Single Dose	Estimated mL/Dose
5 years	18 kg	108 cm	250 mg	10 mg/kg/dose	3	125 mg / 5 mL	180 mg	7.2 mL
18 months	11 kg	82 cm	120 mg	8 mg/kg/dose	4	160 mg / 5 mL	88 mg	2.75 mL
10 years	32 kg	138 cm	400 mg	12 mg/kg/day	2	200 mg / 5 mL	192 mg	4.8 mL

Formula used

Weight-based dosing:
Single dose = Weight (kg) × prescribed mg/kg/dose

Daily weight-based dosing:
Daily dose = Weight (kg) × prescribed mg/kg/day, then divide by doses per day

Mosteller body surface area:
BSA (m²) = √[(Height in cm × Weight in kg) ÷ 3600]

BSA scaling from adult dose:
Child dose = (Child BSA ÷ 1.73) × adult dose

Clark’s Rule:
Child dose = (Weight in lb ÷ 150) × adult dose

Young’s Rule:
Child dose = [Age in years ÷ (Age in years + 12)] × adult dose

Fried’s Rule:
Infant dose = (Age in months ÷ 150) × adult dose

How to use this calculator

Enter the child’s age and current body weight. Weight is the only required body measurement, but height improves BSA estimates.
Type the most specific dosing instruction you have, such as mg/kg/dose, mg/kg/day, mg/m²/dose, or an adult reference dose.
Add the planned doses per day so the calculator can estimate both a single dose and total daily amount.
Enter liquid concentration if you need milliliters, or tablet strength if you need tablets per dose.
Use maximum single and daily doses whenever a label or prescriber provides them.
Press the calculate button. Review the result card above the form, then verify every figure against the medicine label and a clinician’s advice.

FAQs

1. Which method should I trust most?

Use the medicine-specific prescription first, especially mg/kg/dose or mg/kg/day. Age-based rules are older estimates and should only support, not replace, medicine guidance from a clinician or pharmacist.

2. Why can results differ between methods?

Each method scales dose differently. Weight, age, and BSA formulas can produce different answers for the same child. That difference is why label directions and clinical review are essential.

3. Do I need height for every calculation?

No. Height is mainly needed for BSA-based dosing. Weight-based calculations work without height, but BSA can be useful for some medicines that scale by body surface area.

4. Can I use this for infants and newborns?

Use extra caution. Newborn and neonatal dosing often depends on gestational age, postnatal age, organ function, and specialty references. This tool is not a substitute for neonatal prescribing support.

5. What if my child weighs over 40 kg?

Some weight-based calculations may exceed adult dosing. This calculator warns and caps to the adult reference dose when appropriate, but you should still verify the correct product maximum.

6. How is liquid volume calculated?

The tool converts dose milligrams into milliliters using the entered concentration. Example: 125 mg in 5 mL equals 25 mg/mL. A 100 mg dose would therefore equal 4 mL.

7. Why should I enter maximum doses?

Maximum single and daily doses help prevent the estimate from exceeding known product or prescription limits. They add an extra safety check when strong pediatric labeling exists.

8. Does this replace a doctor or pharmacist?

No. It is an educational calculator for checking arithmetic, comparing methods, and converting strengths. Always confirm medicine choice, interval, and final dose with a qualified professional.