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Pediatric Dosage by Weight

Calculate mg/kg doses with built-in safe-dose-range checking. Pick a drug from the prefilled list or enter your own dose. The calculator flags doses outside the published safe range so you spot the trap before the medication record does.

JR
Jordan R., MSN, RN-BCAcute care · 11 yrs · CCRNReviewed 2026-04-30 by L. Chen, PharmD, BCPS

For "Custom" enter the mg/kg dose yourself. Always confirm against your institution's formulary.

Use the most recent dosing weight, not stated weight.

Auto-fills when you select a drug above.

For liquids: lets us also tell you how many mL to draw up.

Result
— mg per dose
Enter weight and dose to calculate.

How peds dosing works

Most pediatric drug doses are written as mg per kilogram (mg/kg) per dose, sometimes per day. Multiply the dose by the patient's weight in kg, and you have the milligrams to administer. Then divide by the medication's concentration (mg/mL) to get the volume to draw up.

The two-step formula:

Dose (mg)  =  weight (kg)  ×  mg/kg
Volume (mL) =  Dose (mg)  ÷  concentration (mg/mL)

Convert pounds to kilograms

If the chart shows weight in pounds, divide by 2.2 (or multiply by 0.4536 for the precise conversion). The calculator above does this automatically when you toggle the unit.

What "safe dose range" means

Every peds drug has a published low and high mg/kg threshold based on age, indication, and drug-specific kinetics. If the order is below the low end, it may be subtherapeutic. If it's above the high end, it's a potential overdose. Bedside nurses and pharmacy both run this check independently — your job is to catch errors that slip through.

NCLEX trap: A question that gives you a one-time loading dose may compute well over the typical mg/kg maintenance range and look unsafe. Read the order: loading doses are intentionally larger.

Worked example

Order: Acetaminophen 15 mg/kg PO q6h PRN fever, child weighs 18 kg.

  1. Per-dose mg: 18 × 15 = 270 mg.
  2. Concentration of available syrup: 160 mg / 5 mL = 32 mg/mL.
  3. Volume to draw up: 270 ÷ 32 = 8.4 mL.
  4. Daily total: 270 mg × 4 doses = 1,080 mg/day. Compare to max 75 mg/kg/day = 1,350 mg/day. Within safe range.

Common pitfalls

  • Using stated weight instead of dosing weight. For obese kids, some drugs use ideal body weight or adjusted body weight; pharmacy will tell you when this applies.
  • Forgetting per-dose vs per-day units. Amoxicillin for otitis is written 80–90 mg/kg/day, not per dose. Divide by frequency before comparing.
  • Skipping the volume step. Knowing the mg dose is half the work — the syringe gets filled with mL.
  • Adult formulary defaults. If your EMR drops in an adult dose for a child, the math will look reasonable but the milligrams will be off by an order of magnitude.

Drill peds dosage calc in NCLEX format

Nursing Ready's pediatrics question bank has 200+ items including weight-based dosing, plus 30 micro-lessons on the high-yield peds topics (sickle cell, croup, dehydration grading). 7-day free trial.

Download on the App Store →
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