BYTETOOLS

Pediatric Dosage Calculator

Convert a mg per kg paediatric dose into milligrams and millilitres, apply single and daily maximums, and compare Clark's and Young's rules.

Child and drug

Caps and concentration

300.0 mg
Dose per administration
6.00 mL
Volume per dose
1,200.0 mg
Total daily dose
60.0
Daily mg/kg

Paracetamol suspension — weight-based dose

300.0 mg = 6.00 mL per dose

mg per kg × weight15.0 × 20.0 kg = 300.0 mg
After the single-dose capno cap applied
Volume per dose300.0 mg ÷ (250 mg ÷ 5 mL) = 6.00 mL
Total daily dose (× 4)1,200.0 mg
After the daily capno cap applied
Total daily volume24.00 mL

Historical rules, for comparison only

MethodFormulaDoseNotes
Weight-based (mg/kg)mg/kg × weight300.0 mgThe only method used in modern paediatric prescribing.
Clark's ruleweight (lb) ÷ 150 × adult dose293.9 mgUses 44.1 lb against a notional 150 lb adult. Ignores the drug entirely, so it is badly wrong whenever clearance does not scale with mass.
Young's ruleage ÷ (age + 12) × adult dose333.3 mgAge-only, so two children of the same age and very different sizes get the same dose. Undefined outside roughly 1–12 years and shown as a dash for an age of 18 or more.
The three methods agree within 25%

Estimates only, not medical advice, and never a prescription. Paediatric dosing errors are one of the most common serious medication errors in hospitals, so every dose calculated here must be checked against the current formulary entry, the actual product label and, where your protocol requires it, an independent second checker. This tool assumes a single strength and a simple mg/kg regimen: it does not know about loading doses, renal or hepatic adjustment, body-surface-area dosing (used for most chemotherapy), neonatal or premature dosing, obesity dose-capping conventions, or the differences between formulations of the same drug. Clark's and Young's rules are included for teaching and exam context only; they are obsolete and should never drive a real dose.

What is the Pediatric Dosage Calculator?

A weight-based paediatric dose is milligrams per kilogram multiplied by the child's weight in kilograms, capped at the maximum single dose. To convert it to a volume, divide the dose in milligrams by the concentration in milligrams per millilitre.

  • Dose in milligrams and millilitres from any mg per mL concentration
  • Separate maximum single dose and maximum daily dose caps, with explicit warnings when they bite
  • Total daily dose and daily mg/kg shown alongside the per-dose figure
  • Clark's rule and Young's rule computed for comparison, with a divergence flag
  • Kilograms or pounds, converted automatically
  • Runs 100% locally in the browser — no patient details are transmitted

How to use the Pediatric Dosage Calculator

  1. 1

    Name the medicine (labelling only), choose kilograms or pounds, and enter the child's weight and age.

  2. 2

    Enter the dose in milligrams per kilogram per dose and how many doses are given each day.

  3. 3

    Set the maximum single dose and maximum daily dose in milligrams — enter 0 for no cap.

  4. 4

    Enter the preparation's strength and the volume it is expressed in, such as 250 mg per 5 mL.

  5. 5

    Read the dose in mg and mL, the daily totals, any cap warnings, and the Clark's and Young's comparison.

About the Pediatric Dosage Calculator

The ByteTools Pediatric Dosage Calculator converts a mg per kg dose into both milligrams and millilitres of a liquid preparation, applies the maximum single and maximum daily dose you enter, and shows the total daily dose and daily mg/kg so you can check the whole regimen rather than one spoonful.

It also computes Clark's rule and Young's rule beside the weight-based figure and flags when the three methods disagree by more than 25%, because those historical rules are still taught and still asked about in exams even though modern practice does not use them. The comparison makes it obvious why weight-based dosing won.

All arithmetic runs in your browser; nothing about the child is uploaded or stored. These are estimates for education and cross-checking only, not medical advice and never a prescription — every dose must be checked against the current formulary entry, the actual product label and your local double-checking policy.

Frequently asked questions

How do you calculate a paediatric dose by weight?

Multiply the milligrams per kilogram from the formulary by the child's weight in kilograms, then check it against the maximum single dose. A 20 kg child at 15 mg/kg gets 300 mg, and with a 250 mg per 5 mL suspension that is 6 mL.

How do I convert a dose in mg to mL?

Divide the dose in milligrams by the concentration in milligrams per millilitre. A 250 mg per 5 mL preparation is 50 mg/mL, so a 300 mg dose is 6 mL. This calculator does the division for you from whatever strength and volume you enter.

What is Clark's rule?

Clark's rule estimates a child's dose as the child's weight in pounds divided by 150, multiplied by the adult dose. It ignores the specific drug entirely, so it goes badly wrong whenever clearance does not scale neatly with body mass. It is historical, not current practice.

What is Young's rule?

Young's rule is age in years divided by age plus 12, multiplied by the adult dose. Because it uses age alone, two children of the same age but very different sizes receive the same dose. Like Clark's rule it is included here for teaching and exam context only.

Why does the calculated dose sometimes get capped?

Because many drugs have a ceiling dose that applies once a child reaches adult size — beyond that point more milligrams per kilogram adds toxicity, not effect. When a cap bites, treat it as a prompt to re-read the label, not as an obstacle to work around.

Is this safe to use for a real prescription?

No. It is a cross-check, not a prescribing tool. It does not know about loading doses, renal or hepatic adjustment, body-surface-area dosing, neonatal regimens or the differences between formulations. Always verify against the current formulary and follow your organisation's independent double-check policy.

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