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Dose (mg/kg)

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General estimate for planning only — not medical advice. Consult a doctor about your specific situation.

Calculation details

Every figure above is calculated locally in your browser from the assumptions shown. No inputs are sent anywhere. See the methodology section below for how this tool works.

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Child dose in mg rising with weight against a 500 mg cap — An 18 kg child at 15 mg/kg takes 270 mg, or 5.4 mL.

Method & verification

How This Tool Works

fact-checked against our calculation methodology

Calculation Method

Computes Single dose from Weight, Unit and Dose.

Site methodology

BoringToolsKit methodology and verification standard

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Assumptions to Verify

These tools provide general estimates for planning and education only.
They are not medical advice and not a substitute for a qualified healthcare professional.
Always consult your doctor or another healthcare provider about your specific situation.

Privacy: The calculation runs in this browser. Shared links contain the page address only, not your inputs or results.

Worked example: an 18 kg child at 15 mg/kg

Say a prescriber orders 15 mg/kg for a child weighing 18 kg. The calculator multiplies 18 x 15 = 270 mg per single dose. If the suspension on hand is 250 mg per 5 mL, that dose equals 270/250 x 5 = 5.4 mL, which most oral syringes measure exactly.

The weight-unit switch matters more than people expect. Enter the same child as 40 pounds and the tool converts first: 40 x 0.453592 = 18.14 kg, then 18.14 x 15 = 272.1 mg, displayed as 272 mg. That 2 mg gap is pure rounding of the pound-to-kilogram step, not a dosing difference. Clinicians work in kilograms for this reason; if you only know pounds, check the kilogram figure the tool shows in the result line before drawing up a volume.

A second sanity check: the dose per kilogram times the dose count gives the daily total. Three 270 mg doses in 24 hours is 810 mg/day, which you can compare against the maximum daily mg/kg limit printed on the label.

Where a single mg/kg number breaks down

mg/kg dosing is a straight-line assumption, and bodies are not straight lines. Many pediatric labels cap the dose at a fixed maximum, for example 500 mg per dose or 2,000 mg per day, whichever comes first. A 55 kg teenager at 15 mg/kg computes to 825 mg, but if the cap is 500 mg the calculator output is simply wrong for that drug. Always check whether the prescriber label states a maximum before trusting a scaled number.

Obesity is the other edge case. Adipose tissue is less perfused than lean mass, so some drugs are dosed on adjusted body weight instead of actual weight; using total kilograms can overstate the dose by 20 to 40 percent for those medicines. The calculator cannot tell which dosing weight the prescriber intended.

Young infants often use weight bands or fixed doses below roughly 3 months of age, and some drugs are dosed per body surface area rather than per kilogram. In all three cases, the tool gives a useful first figure but the labeled or prescribed instruction wins. This page is a check-the-arithmetic aid, not a substitute for the prescription.