Amoxicillin dosing for children is not one number — it depends on which infection is being treated, the child's age and weight, and whether the regimen comes from the FDA label or a professional-society guideline. This calculator turns a weight, age, and indication into a per-dose amount in milligrams and milliliters, checks it against a per-dose safety cap, and clearly labels whether the range is FDA-approved or a clinical-guideline recommendation.

Why the indication matters

Amoxicillin's FDA label sets two standard dosing tiers based on infection severity and site — 25 mg/kg/day for mild/moderate ear, nose, throat, skin, and urinary-tract infections, and 45 mg/kg/day for severe infections in those same sites or any lower-respiratory infection. Neither of these reaches the commonly-used 80-90 mg/kg/day 'high-dose' regimen for acute otitis media and sinusitis — that range comes from the AAP's 2013 Otitis Media guideline and the IDSA's 2012 Sinusitis guideline, not from amoxicillin's own FDA-approved label. Strep pharyngitis dosing (50 mg/kg once daily, or 25 mg/kg twice daily) similarly comes from the IDSA's Group A Strep guideline. This calculator selects the correct range for the chosen indication and marks each one with a source badge — green for FDA label, amber for guideline — so the distinction is never hidden.

The 3-month and 40 kg safety cutoffs

Two cutoffs override the normal indication-based math. Infants 3 months old or younger have incompletely developed renal function, so the FDA label reduces the ceiling to 30 mg/kg/day divided every 12 hours regardless of the selected indication or the child's weight. At the other end, the FDA label states that children weighing 40 kg or more should be dosed according to the adult recommendations rather than the pediatric mg/kg tables — this calculator switches to a fixed adult dose at that point instead of extrapolating the weight-based formula, which could otherwise produce a dose above the intended adult ceiling.

Reading a concentration and converting mg to mL

Liquid amoxicillin is labeled as an amount of drug in a stated volume — commonly 125, 200, 250, or 400 mg per 5 mL, though no single product carries all four strengths. Divide the amount by the volume to get the concentration in mg/mL, then divide the dose in mg by that concentration to find the volume to measure. Always read the concentration printed on the specific bottle in hand — it varies by product and has been reformulated over the years.

The per-dose cap

Each indication and frequency combination carries an explicit per-dose cap in milligrams, independent of the mg/kg math — for example 500 mg per dose for standard-mild twice-daily dosing, or 1000 mg for once-daily strep pharyngitis. A larger child's calculated mg/kg dose can exceed this cap even when the mg/kg rate itself is correct; when that happens, the verdict turns red and the actual dose given should not exceed the cap without a prescriber or pharmacist's explicit direction.

This calculator is for educational reference only

This tool performs indication-based dosing arithmetic using published FDA-label and clinical-guideline ranges. It does not know a specific child's allergies, renal or hepatic function, drug interactions, or whether amoxicillin is the right antibiotic for their infection — that judgment belongs to a licensed prescriber and pharmacist. Use the result to check your own math and catch unit or indication mix-ups, not to decide or change a dose. For clinical/educational reference only. Not a substitute for clinical judgment. Verify all doses with a pharmacist or current prescribing information before administering.