Pediatric Weight-Based Dose Calculator

Almost all pediatric prescriptions are weight-based: the dose is given as milligrams per kilogram of body weight per dose, often abbreviated as mg/kg/dose. This calculator converts that into a concrete per-dose milligram amount, the daily total, the full course quantity, and (if liquid) the volume in milliliters.

The basic formula:

per-dose mg = weight (kg) × mg/kg/dose

Almost every pediatric medication has a maximum single dose, beyond which adult dosing applies regardless of weight. Larger children might calculate above that cap; the calculator applies the cap and shows whether it took effect.

daily total = per-dose × doses per day course total = daily × days

For liquid medications: volume per dose (mL) = per-dose mg ÷ concentration (mg/mL). Useful for dispensing the right syringe size and for checking whether the daily volume is realistic for the child to swallow.

Worked example: 15 kg child, ibuprofen 10 mg/kg per dose, max 400 mg per dose, every 8 hours (3 doses/day), liquid is 100 mg/5 mL (= 20 mg/mL).

Per dose = 15 × 10 = 150 mg. Below the 400 mg cap, so 150 mg stands. Volume per dose = 150 ÷ 20 = 7.5 mL. Daily total = 150 × 3 = 450 mg. Day 1 volume = 7.5 × 3 = 22.5 mL.

For a 5-day course: 450 mg a day × 5 = 2,250 mg total medication, and 22.5 mL a day × 5 = 112.5 mL of liquid, which is reasonable for one bottle.

(Check that against itself: 112.5 mL at 20 mg/mL is 2,250 mg. The two figures have to agree, and this is exactly the cross-check the calculator is for.)

The daily total needs checking too, and most people only check the single dose. A per-dose cap does not stop you from going over the day’s limit, because the two are separate numbers. Acetaminophen is the clearest case: 15 mg/kg a dose is correct, and so is a 1,000 mg per-dose ceiling, but the daily maximum is 75 mg/kg, which works out at five doses and no more. Give a correct dose six times and every single dose was right while the day was 20% over. There is a daily-maximum box below for exactly this, and it is worth filling in.

Why this matters: dosing errors are the most common medication-related cause of pediatric hospital visits. Two common categories are decimal mistakes (10 mg/mL written as 10.0 mg/mL with the decimal misread as a different digit) and concentration confusion, where the same drug is sold at several strengths. The 2011 US switch of infant acetaminophen drops from 80 mg/0.8 mL to 160 mg/5 mL is the famous one, and old bottles were in cupboards for years afterwards at triple the new concentration. This calculator checks the per-dose amount and the volume in mL together, so a concentration mix-up shows up as a volume that looks obviously wrong.

Always cross-check three times against the original prescription: the mg/kg/dose, the maximum dose, and the concentration. Two adults reviewing independently is the recommended safety practice in hospitals. At home, ask your pharmacist to walk through the syringe markings before the first dose if the medication is new to your child.

This tool is a math helper, not a prescribing reference. Specific drug doses, maximum doses, and frequencies must come from the prescribing clinician or an authoritative pediatric formulary like the AAP’s Red Book or Lexicomp Pediatric.