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Amoxicillin Pediatric Dosage Calculator

Amoxicillin remains the most frequently prescribed antibiotic in pediatric practice, used to treat bacterial infections ranging from otitis media to streptococcal pharyngitis. Determining the correct dose requires careful attention to a child's weight, age, indication, and route of administration. This calculator applies evidence-based dosing recommendations to help verify whether a prescribed dose falls within safe therapeutic ranges for your patient.

Last updated:

Creators Adena Benn, BSc
6,172 people find this calculator helpful

Understanding Amoxicillin in Pediatric Practice

Amoxicillin is a beta-lactam antibiotic effective against a broad spectrum of gram-positive and some gram-negative bacteria. In pediatrics, it is the first-line choice for common infections including acute otitis media, community-acquired pneumonia, and group A streptococcal pharyngitis.

When formulated as an oral suspension, amoxicillin is well-tolerated and achieves excellent tissue penetration. Intravenous formulations are reserved for serious infections or patients unable to take oral medications. The drug is rapidly absorbed and primarily eliminated unchanged in urine, making dose adjustment unnecessary for renal impairment in most cases.

Dosing strategy varies significantly by indication. Uncomplicated infections typically require 15–30 mg/kg per dose, while more serious conditions like endocarditis prophylaxis or severe pneumonia demand higher loading doses. Always verify the specific indication before calculating, as this fundamentally alters the therapeutic target.

Amoxicillin Dosage Formulas

Weight-based dosing underpins pediatric amoxicillin calculation. The following formulas determine both the minimum therapeutic dose and safe maximum limits for oral and intravenous routes:

Minimum oral dose (mg) = Child's weight (kg) × 15 mg/kg

Minimum oral volume (mL) = Minimum dose ÷ Suspension strength (mg/mL)

Minimum IV dose (mg) = Child's weight (kg) × 30 mg/kg

Minimum IV volume (mL) = Minimum IV dose ÷ Concentration (mg/mL)

Your dose (mg) = Recommended dose per kg × Child's weight (kg)

Maximum oral dose (mg) = Minimum dose × 2

Maximum daily dose = 4 g (4000 mg) per day

  • Weight — Child's body weight in kilograms or pounds
  • Strength — Amoxicillin concentration of the suspension or solution (mg/mL)
  • Dose — Recommended dose range for the specific indication (mg/kg/dose)
  • Maximum daily dose — Upper limit for total daily amoxicillin (typically 4 g for most indications)

How to Use the Pediatric Amoxicillin Calculator

Begin by entering your child's age (in months or years) and weight in your preferred unit. The calculator accepts kilograms, pounds, and stones, converting automatically. Next, select the amoxicillin strength — this refers to the concentration of the liquid suspension (e.g., 250 mg/5 mL or 400 mg/5 mL) or the solid form strength if applicable.

Choose the clinical indication from the provided options: general bacterial infection, streptococcal pharyngitis, or endocarditis prophylaxis. Each indication carries different dosing recommendations per international guidelines. Finally, select the route of administration—oral (per os) or intravenous.

The calculator will display the recommended dose range in both milligrams and millilitres, along with the maximum safe single dose and daily total. Compare these values against what your healthcare provider has prescribed to ensure alignment with current evidence-based recommendations.

Dose Adjustments by Indication and Route

General bacterial infections (uncomplicated otitis, urinary tract infections): 15–30 mg/kg per dose, given three times daily (every 8 hours). Oral route is standard; intravenous reserved for hospitalised patients or severe cases.

Streptococcal pharyngitis: Dosing depends on weight. Children under 15 kg receive 50 mg/kg per dose. Those 15–29 kg receive a fixed 750 mg dose. Children over 30 kg receive 1000 mg per dose. This shift to fixed dosing above 15 kg reflects mature pharmacokinetics.

Endocarditis prophylaxis: A single large dose (typically 2 g maximum) given 30–60 minutes before the procedure. This is quite different from therapeutic dosing and must not be confused with treatment regimens.

Intravenous dosing: The IV dose range is 30–60 mg/kg per dose (double the oral range), used for severe infections or when oral intake is not feasible. The maximum single IV dose is 1 g, with a daily cap of 4 g.

Critical Considerations When Dosing Amoxicillin

Accurate dosing requires attention to several practical pitfalls and real-world variables that affect safety and efficacy.

  1. Verify suspension strength before calculating volume — Liquid amoxicillin suspensions are available in multiple strengths (typically 125 mg/5 mL, 250 mg/5 mL, or 400 mg/5 mL). Confusing the strength leads to dangerous under- or overdosing. Always check the label three times when measuring—at preparation, measurement, and administration.
  2. Account for weight fluctuations in growing children — A child's weight affects dosing calculations directly. If more than a few weeks have passed since the last recorded weight, remeasure before dispensing. Weight gain or loss, even modest, can shift a dose calculation significantly, particularly near dosing thresholds (e.g., the 15 kg cutoff for strep dosing).
  3. Do not confuse per-dose with per-day calculations — Some indications specify mg/kg per dose (given multiple times daily), while others use mg/kg per day (divided into doses). Multiplying a per-day figure by weight and giving it as a single dose is a common error. Always verify whether the recommendation is per dose or per day before calculating.
  4. Be aware of hypersensitivity risk in penicillin-allergic patients — Amoxicillin is a penicillin and carries a 1–3% cross-reactivity risk with cephalosporins in penicillin-allergic patients. Always obtain a detailed allergy history and document the type of reaction (rash, anaphylaxis, etc.) before prescribing. If allergy is confirmed, select an appropriate non-beta-lactam alternative.

Frequently Asked Questions

What is the correct amoxicillin dose for a 10 kg child with an ear infection?

For uncomplicated otitis media in a 10 kg child, the typical dose is 15–30 mg/kg per dose. This equals 150–300 mg per dose. If the suspension strength is 250 mg/5 mL, that corresponds to 3–6 mL per dose, given three times daily (every 8 hours). The maximum daily dose remains 4 g (4000 mg). Always confirm the specific indication and suspension strength with the prescribing information or your healthcare provider, as dosing can vary based on local guidelines and infection severity.

How do you calculate the millilitre dose from a milligram dose?

Divide the dose in milligrams by the suspension strength (mg/mL). For example, if the recommended dose is 300 mg and the suspension is 250 mg/5 mL (which equals 50 mg/mL), the volume is 300 ÷ 50 = 6 mL. If the suspension is labeled as strength per total volume (e.g., 250 mg/5 mL), first convert to mg/mL by dividing: 250 ÷ 5 = 50 mg/mL, then proceed. Always use a calibrated syringe, not a household spoon, to ensure accuracy.

What is the maximum daily dose of amoxicillin for children?

The maximum daily dose is 4 g (4000 mg) for most indications in children. However, the maximum per single dose differs by route: 500 mg for oral administration and 1000 mg for intravenous administration. These limits exist to prevent toxicity and adverse effects. For endocarditis prophylaxis, the single dose maximum is 2 g (given as one dose, not divided throughout the day). Always confirm dosing limits in current prescribing guidelines, as recommendations may be updated.

Why does amoxicillin dosing change at 15 kg for strep throat?

Below 15 kg, weight-based dosing (mg/kg) provides an appropriate therapeutic dose. Above 15 kg, children's pharmacokinetics and clearance approximate adult patterns, so fixed doses (750 mg or 1000 mg) become more practical and equally effective. This transition prevents unnecessary high dosing in heavier children while ensuring adequacy in lighter adolescents. The 15 kg threshold is based on clinical evidence and is used internationally in most treatment guidelines.

Can amoxicillin suspension be mixed with food or drink?

Amoxicillin suspension can be mixed with small amounts of soft foods or drinks to mask the taste, though this is less common with modern flavored formulations. If mixing is necessary, use foods that will be consumed entirely (e.g., applesauce, yoghurt) rather than foods a child might leave partially uneaten. Never mix with hot drinks, as heat may degrade the antibiotic. Always administer the full mixed dose immediately to avoid settling or separation. Check the product information sheet for any specific contraindications regarding mixing.

What should you do if a child vomits shortly after taking amoxicillin?

If vomiting occurs within 30 minutes of administration, repeat the dose. If vomiting occurs after 30 minutes, the dose is likely absorbed sufficiently; do not repeat. Monitor the child for signs of continued infection and contact the prescribing healthcare provider if you are uncertain. Never double the next scheduled dose to compensate for a missed dose—simply resume the normal schedule. If vomiting is persistent or the child shows signs of dehydration, seek medical advice promptly.

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