mg/kg to milligrams, milligrams to millilitres at the strength you have, split across divided doses, with a hard-stop check against the maximum dose you set. No account, no data leaves the page.
What it calculates. Dose in mg = mg/kg ร weight. Volume in mL = dose in mg รท strength in mg/mL. If the prescription is written as mg/kg per 24 hours, the total is divided by the number of doses to give the amount per administration. In reverse mode you type a milligram figure and it reports the mg/kg that figure represents at the weight entered โ the fastest way to check whether an adult dose you have been given is a sane one for a small patient.
Worked example. An 18 kg child, paracetamol 15 mg/kg per dose, 4 doses a day, suspension 50 mg/mL: 15 ร 18 = 270 mg per dose; 270 รท 50 = 5.4 mL; over 24 hours that is 270 ร 4 = 1080 mg = 60 mg/kg/day. Set the maximum to 1000 mg and the tool flags the dose as safe with 730 mg of headroom; set it to 250 mg and it flags an exceedance.
The errors this tool exists to catch. (1) Strength and concentration are different things โ "amoxicillin 250/5" means 250 mg in 5 mL, which is 50 mg/mL, not 250 mg/mL; entering the packet number rather than the concentration is the single most common paediatric volume error and it is out by the dilution factor. (2) mg/kg per dose versus mg/kg per day are routinely confused; pick the unit in the dropdown rather than remembering it. (3) A maximum applies per dose and per 24 hours; both fields are here because a dose can be fine and the day can still be over. (4) Not everything is weight-based โ adrenaline for anaphylaxis, nebulised salbutamol and naloxone in adults are given as fixed or age-banded doses, and forcing them through a mg/kg calculation is how errors happen. (5) Chemotherapy and some other agents are dosed per square metre of body surface area, not per kilogram; use the Body Surface Area Calculator for those.
The reference table below is a prompt, not a prescription. The figures are typical UK BNF / BNFC values, included so that a weight-based number lands next to something recognisable. They are not complete, not indication-specific, not adjusted for renal or hepatic function, age bands, neonatal status or interaction, and they are not a substitute for the current edition of the BNF, the BNFC, the product SPC or your trust formulary. Verify before you prescribe.
Other limits. The weight used is whatever you type โ in obesity many agents are dosed on ideal or adjusted body weight, and in neonates on current weight with a different dosing interval entirely. Nothing here knows the indication, the formulation, the route or the patient's organ function.
Disclaimer. Arithmetic for qualified clinicians, offered as a second pair of eyes and not as medical advice. Independent double-checking of any dose against an authoritative source remains the responsibility of the prescriber and the person administering it. Sources: typical BNF / BNFC dose ranges ยท Resuscitation Council UK anaphylaxis guidance. Last reviewed: 2026-09-21.