If you’re calculating a child’s amoxicillin dose, use weight (mg/kg/day) plus the dosing schedule (e.g., twice daily) to convert to a practical amount per dose. This guide explains the standard dosing math and shows how to use the calculator safely and correctly.
Important: amoxicillin dosing depends on the infection type, severity, kidney function, and local guidelines. Always follow your clinician’s prescription and verify the final dose with a healthcare professional.
How pediatric amoxicillin dosing works
Pediatric dosing is usually based on the child’s weight and an ordered total daily dose in mg/kg/day. Then the total daily dose is divided into the number of doses per day (for example, 2 doses for twice daily).
Clinicians commonly express dosing as:
- Total daily dose (mg/day) = weight (kg) × prescribed mg/kg/day
- Per-dose amount (mg/dose) = total daily dose ÷ doses per day
- Volume to give (mL/dose) = per-dose amount ÷ concentration (mg/mL)
What the variables mean
Below are the inputs you’ll see in the calculator and how they map to the dosing formula.
| Input | Meaning | Typical unit |
|---|---|---|
| Child weight | Used to compute mg/kg/day | kg or lb |
| Prescribed regimen (mg/kg/day) | The clinician’s total daily dose order | mg/kg/day |
| Doses per day | How often the child takes the medicine | 1, 2, or 3 |
| Amoxicillin concentration | How many mg are in each mL of liquid | mg/mL |
Core formulas (weight-based)
These are the exact calculations the calculator performs.
- Weight conversion: kg = lb ÷ 2.2046
- Total daily dose: mg/day = kg × (mg/kg/day)
- Per-dose dose: mg/dose = (mg/day) ÷ (doses/day)
- Volume per dose: mL/dose = (mg/dose) ÷ (mg/mL)
Because liquid concentration is a common source of dosing mistakes, the calculator requires you to enter the concentration you have on hand.
Common dosing regimens (use your prescription)
Many pediatric prescriptions fall into a few common ranges. However, you must select the regimen that matches the prescription instructions you were given.
- Lower range regimens are sometimes used for mild infections.
- Higher range regimens may be used for certain infections or severity.
- Twice-daily or three-times-daily schedules change the per-dose amount even when the total daily dose stays the same.
If your clinician wrote an order like “amoxicillin 400 mg/5 mL,” that is a concentration. The calculator can use that to compute mL per dose once you also enter the mg/kg/day regimen.
How to find the concentration on the bottle
Liquid amoxicillin labels often show a strength such as:
- 400 mg/5 mL
- 250 mg/5 mL
To use the calculator, you need mg/mL. Convert as follows:
- mg/mL = (mg in the label) ÷ (mL in the label)
- Example: 400 mg/5 mL = 400 ÷ 5 = 80 mg/mL
If your label uses mg/5 mL, enter the equivalent mg/mL in the calculator.
Practical example #1: twice-daily liquid dosing
Suppose a child weighs 24 lb and the prescription is 45 mg/kg/day given twice daily. The bottle is 400 mg/5 mL, which equals 80 mg/mL.
- Weight: 24 lb ÷ 2.2046 ≈ 10.9 kg
- Total daily dose: 10.9 × 45 ≈ 491 mg/day
- Per dose (twice daily): 491 ÷ 2 ≈ 245.5 mg/dose
- Volume per dose: 245.5 ÷ 80 ≈ 3.07 mL/dose
Your actual prescription may differ. This math shows how mg/kg/day turns into mL per dose.
Practical example #2: once-daily dosing schedule check
Now imagine a child weighs 30 lb and the prescription is 25 mg/kg/day given once daily. The liquid concentration is 250 mg/5 mL = 50 mg/mL.
- Weight: 30 ÷ 2.2046 ≈ 13.6 kg
- Total daily dose: 13.6 × 25 ≈ 340 mg/day
- Per dose (once daily): 340 ÷ 1 = 340 mg/dose
- Volume per dose: 340 ÷ 50 = 6.8 mL/dose
Notice how the same mg/kg/day order would produce a different per-dose volume if the schedule changes.
Safety notes you must follow
- Verify the mg/kg/day regimen with the prescription. Don’t guess the regimen from symptoms.
- Confirm the liquid concentration on the bottle. mg/5 mL and mg/mL mistakes are common.
- Check the dosing frequency. Twice daily vs three times daily changes the per-dose amount.
- Do not exceed prescribed maximums (clinicians may cap doses depending on age and indication).
- Kidney problems may require dose adjustments. Ask your clinician if your child has kidney disease.
If your child has trouble swallowing, severe vomiting, or signs of allergy (rash, swelling, breathing issues), seek medical help immediately.
How to use the Amoxicillin Pediatric Dosage Calculator
Enter your child’s weight, the mg/kg/day regimen from the prescription, the dosing frequency, and the bottle concentration. The calculator returns:
- Total daily dose in mg/day
- Dose per administration in mg/dose
- Volume per dose in mL/dose
- Optional supporting values like weight in kg and converted concentration
Use the results to confirm what you were told—not to replace medical advice.
Frequently Asked Questions
What does mg/kg/day mean for amoxicillin?
mg/kg/day is the prescribed total daily amount of amoxicillin measured in milligrams for each kilogram of body weight. To calculate the daily dose, multiply the child’s weight in kg by the mg/kg/day value. Then divide by the number of doses per day to get mg per dose.
How do I convert 400 mg/5 mL into mg/mL?
To convert mg per 5 mL to mg per 1 mL, divide by 5. For 400 mg/5 mL, 400 ÷ 5 = 80 mg/mL. Enter 80 mg/mL in the calculator so it can convert mg per dose into mL per dose accurately.
Why does the mL per dose change if the schedule changes?
The total daily dose stays the same when the mg/kg/day order is unchanged. If you change from twice daily to once daily, you divide the daily mg by a different number of doses. Fewer doses per day means a larger mL per dose.
Can I use this calculator for tablets or capsules?
This calculator focuses on weight-based dosing and liquid volume conversions using concentration in mg/mL. For tablets or capsules, you must convert mg/dose into the nearest appropriate tablet strength, based on what your clinician prescribed. Always confirm the final rounded dose with your pharmacist.
When should I contact a clinician before giving amoxicillin?
Contact a clinician before dosing if the child has kidney disease, a known allergy to penicillins, or severe vomiting that prevents keeping medicine down. Also verify dosing if the prescription instructions are unclear, the concentration label differs, or the child’s weight has changed significantly since the visit.