Amoxicillin Pediatric Dosage Calculator

Liquid amoxicillin is a suspension the pharmacy mixes from powder, and its strength is written as mg in every 5 mL, such as 400 mg/5 mL. The prescriber sets the dose in mg, and that dose has to become a volume you can draw into an oral syringe. The volume depends on the bottle's strength.

What the Amoxicillin Pediatric Dosage Calculator Measures

It measures volume, not dose. You bring the mg dose from the prescription and the strength from the bottle, and it shows mL per dose, mL per day and how long the bottle lasts. It does not ask for weight or age, and it does not suggest, check or change a dose.

The Formula

mL per dose = prescribed dose (mg) x 5 / bottle strength (mg per 5 mL)

mL per day = mL per dose x doses per day

Days a bottle lasts = bottle size (mL) / mL per day

US amoxicillin suspension comes in 125, 200, 250 and 400 mg per 5 mL, each stated per 5 mL¹ ².

How This Calculator Computes Your Result

Enter the mg for one dose, times a day and the bottle strength; bottle size and days prescribed are optional. The tool shows each step, gives volumes to up to 3 decimals, and lists the same dose at the other strengths so a mismatch with your pharmacy label stands out. It checks the volume against syringe lines every 0.1, 0.2 and 0.5 mL and warns if it falls between lines, is under 0.1 mL or is over 20 mL, if the course needs more than the bottle, or if doses run past 14 days after mixing.

What Your Result Means

Your result is the volume that holds the prescribed mg at your bottle's strength. For a 400 mg/5 mL bottle, each mL holds 80 mg and each 0.1 mL holds 8 mg. Example only: a 400 mg dose is 400 x 5 / 400 = 5 mL, and a 250 mg dose is 3.125 mL.

The same dose needs a very different volume in each bottle: 250 mg is 10 mL of 125 mg/5 mL but 3.125 mL of 400 mg/5 mL. An mL amount from an earlier bottle, a sibling or a website may not fit this one.

When a result falls between lines, the tool shows the mg at the nearest lines (at 400 mg/5 mL, 3.1 mL holds 248 mg and 3.2 mL holds 256 mg), and your pharmacist can tell you which line to use. This page does not replace the label, the prescription or a pharmacist.

FDA Label Dosing Table for Children (Reference Only)

This table is quoted from the FDA prescribing information¹. It is not linked to the calculator. Follow the prescription label; ask your pharmacist if the numbers do not match.

Infections caused by bacteria with intermediate susceptibility follow the severe rows, and for babies under 12 weeks "the recommended upper dose of amoxicillin is 30 mg/kg/day divided every 12 hours"¹. Children over 40 kg follow the label's adult column¹.

Prescribed doses can be higher than this table for good reason. For ear infections, a current federal clinician guide calls high-dose amoxicillin (45 mg/kg per dose every 12 hours) the preferred choice when an antibiotic is prescribed³. A dose that differs from the table is not by itself an error.

Giving, Storing and Finishing Liquid Amoxicillin

The label says "SHAKE ORAL SUSPENSION WELL BEFORE USING" and to keep the bottle tightly closed¹. An oral syringe is usually the most accurate tool, especially for amounts under 5 mL⁴. In a trial of 2,110 parents, 84.4% made at least one error over 20%, and cups caused far more errors than syringes, especially for small doses⁵. The NHS warns that a kitchen teaspoon will not measure the right amount⁶. The AAP advises squirting the dose gently between the tongue and the side of the mouth, not into the back of the throat⁴.

After mixing, refrigeration is preferable but not required, and any unused suspension must be thrown away after 14 days¹. For a missed dose, the NHS says to give it when you remember unless the next one is nearly due, and never to give 2 doses at once⁶.

The label asks that amoxicillin "be taken exactly as directed," even though children often feel better early, because skipping doses or stopping early may make treatment less effective and resistant bacteria more likely¹. Course length varies: for ear infections, the AHRQ guide lists 10 days under age 2 or for severe symptoms, 7 days at 2 to 5 years, and 5 to 7 days at 6 and older³. The prescription label gives your child's number of days.

Allergy Warning Signs That Need Urgent Care

Amoxicillin is a penicillin, and serious, occasionally fatal allergic reactions (anaphylaxis) have been reported¹. The NHS treats these as an emergency needing a call right away (999 in the UK, 911 in the US): sudden swelling of the lips, mouth, throat or tongue; very fast breathing or struggling to breathe; a tight throat; skin, tongue or lips turning blue, grey or pale; or a child who is limp, floppy or not responding like they normally do⁷.

The label also warns of severe skin reactions and of drug-induced enterocolitis syndrome, seen mostly in children: repeated vomiting 1 to 4 hours after a dose, without skin or breathing symptoms¹. It tells patients to stop amoxicillin and promptly report the first signs of a skin rash, mucosal lesions (sores on moist surfaces such as the inside of the mouth) or any other allergic sign¹.

If a child takes more than prescribed, the NHS says one extra dose is unlikely to cause harm⁶. Poison Control gives free, confidential advice at 1-800-222-1222 (US); call 911 if the child collapses, has a seizure, has trouble breathing or cannot be woken⁸.