Acetaminophen — the active ingredient in Tylenol and many store-brand fever and pain medicines — is one of the most common treatments parents give children. It is also one of the easiest medicines to under-dose (so the fever stays up) or over-dose (so you risk liver injury), because the right amount depends almost entirely on your child's current weight, not on age. This acetaminophen dosage calculator turns a body weight and the bottle's concentration into the exact milligram dose and the exact liquid volume in milliliters, so you are not guessing against a blurry dosage chart. The weight-based mg/kg regimen below follows the pediatric dosing guidance published by the American Academy of Pediatrics and the U.S. National Library of Medicine, but it is an educational estimate, not a prescription.
Adjust the inputs and every figure updates instantly. You can switch between the 10 mg/kg mild-pain dose and the 15 mg/kg standard dose, point the calculator at the concentration on your specific bottle, and see both the single dose and the 24-hour ceiling so you never drift into unsafe territory.
How to Use
- Enter your Child's Weight in kilograms. Weigh the child on a scale if you can; estimating weight by age is the number-one cause of dosing errors. If the bottle chart uses pounds, divide pounds by 2.2 to get kilograms.
- Choose the Dose Strength. Use 15 mg/kg for a standard fever or pain dose; use 10 mg/kg if a clinician has advised a lighter dose or you are combining medicines. The accepted pediatric range is 10–15 mg/kg per administration.
- Set the Liquid Concentration from the label. The default, 160 mg per 5 mL, is the most common children's oral suspension. Infant drops and store-brand concentrated liquids can differ, so always read the bottle.
- Enter how often you plan to dose under Doses per 24 h. You may repeat a dose every 4–6 hours, but never more than 5 times in 24 hours.
- Read the result card: the mg per dose, the mL per dose (what you actually draw into the syringe), and the safe maximum over 24 hours in both mg and mL.
The engine rejects a weight of zero or a negative weight, and it assumes a positive concentration so it can convert milligrams into a measurable liquid volume.
The Pediatric Dosing Formula
Children's acetaminophen is dosed by body weight because an infant and a six-year-old can weigh ten times apart. The standard formulas are:
- Single dose (mg) = weight (kg) × dose (mg/kg)
- Liquid dose (mL) = dose (mg) × 5 ÷ concentration (mg per 5 mL)
- Daily ceiling (mg) = weight (kg) × 75 mg/kg/day
Worked example: a 20 kg child at the standard 15 mg/kg dose needs 20 × 15 = 300 mg. With a 160 mg/5 mL suspension, that is 300 × 5 ÷ 160 = 9.375 mL — roughly a little less than two teaspoonfuls. The 24-hour ceiling for that child is 20 × 75 = 1,500 mg, which works out to about 46.9 mL of the same liquid across the whole day.
Notice how the concentration drives the volume. If you mistakenly used infant drops at 160 mg per 1 mL instead of 160 mg per 5 mL, the same 300 mg would need only 1.9 mL. That five-fold difference is why reading the label matters more than memorizing a number. The liquid is about a 3.2% suspension by weight, and a typical bottle costs only $4–$8, so there is no reason to reuse an old syringe for a new product.
Why Weight, Not Age
Age-based dosage tables are shortcuts. A 4-year-old can weigh anywhere from 14 kg to 22 kg, and dosing the high end of that range for a small child is an overdose while dosing the low end for a large child does nothing. Weight-based dosing removes the guesswork: every kilogram of body weight corresponds to a known milligram amount, and the liver clears the drug predictably within that 10–15 mg/kg band. Stay under the 75 mg/kg-per-day ceiling, leave at least 4 hours between doses, and ask a clinician before dosing a child under about 12 weeks old.
Adult Dosing Note
This calculator is built for weight-based children's dosing, and adults should not simply scale the mg/kg formula up. If an adult is treating themselves, follow the exact dosing panel printed on the medicine package and stay within the package's stated 24-hour maximum. Because acetaminophen is hidden in many combination cold, flu, and sleep products, the single most important safety habit is adding up every milligram taken in a day from every bottle and tablet. People who drink alcohol regularly or have liver disease should ask a clinician before using acetaminophen at all. For a precise adult dose, read the label or speak with a pharmacist rather than using this child-weight tool.
Examples
Example 1 — A feverish toddler. A child weighs 20 kg. You select the standard 15 mg/kg dose and a 160 mg/5 mL bottle. The result card shows a 300 mg dose = 9.4 mL, with a 1,500 mg (≈46.9 mL) daily ceiling. At 4 doses across the day you are well under the limit.
Example 2 — A lighter dose for a smaller baby. A 10 kg infant on the mild 10 mg/kg plan takes 10 × 10 = 100 mg = 3.1 mL, and the 24-hour ceiling is 750 mg (≈23.4 mL). Using the low end means roughly a 33% smaller volume per dose than the standard plan, so it is worth re-measuring with the oral syringe rather than eyeballing it.
Example 3 — Comparing concentrations. The same 300 mg child's dose on a 160 mg/5 mL liquid needs 9.4 mL, but on a concentrated 160 mg/mL infant product it needs under 2 mL. Always type the exact concentration printed on your bottle into the calculator — swapping one product for another without recalculating is the most common dosing mistake.
FAQ
What is the standard pediatric acetaminophen dose?
The standard oral dose is 10–15 mg per kilogram of body weight, given every 4–6 hours as needed. For a 20 kg child that is 200–300 mg per dose. Never exceed 75 mg/kg in any 24-hour period, and do not give more than 5 doses per day.
How do I convert the milligram dose into milliliters?
Multiply the milligram dose by 5, then divide by the concentration shown on the bottle in mg per 5 mL. For a common 160 mg/5 mL suspension, a 300 mg dose becomes 300 × 5 ÷ 160 = 9.375 mL. Use the oral syringe that came with the bottle, not a kitchen spoon.
Can I dose acetaminophen by age instead of weight?
Age charts are rough estimates and frequently under-dose or over-dose. A 4-year-old can weigh 14 kg or 22 kg. Always dose by the child's actual weight in kilograms, which this calculator does. If you do not know the weight, ask a pharmacist or pediatrician before dosing.
What is the maximum daily amount of acetaminophen for a child?
The safe ceiling is 75 mg per kilogram of body weight per 24 hours. For a 20 kg child that is 1,500 mg per day. Count every source, including combination cold medicines, because acetaminophen is hidden in dozens of over-the-counter products.
How often can I repeat a dose?
You may repeat the dose every 4–6 hours while symptoms last, but no more than 5 times in 24 hours. Space doses evenly and do not give a "booster" early just because the fever has not fully dropped. If the fever lasts more than a couple of days or the child looks unwell, contact a clinician.
Is liquid acetaminophen the same concentration everywhere?
No. Most children's suspension is 160 mg per 5 mL, but infant drops and some store brands are more concentrated. Always enter the exact mg-per-5 mL value printed on your bottle. Wrong concentration is the leading cause of dosing errors, not the math itself.
How much acetaminophen should an adult take?
This calculator is tuned for weight-based children's dosing, so it is not the right tool for an adult dose. Adults should follow the milligram dosing panel printed directly on their specific bottle or blister pack and respect that package's 24-hour maximum. Always count acetaminophen from every source — combination cold, flu, and sleep products often hide a full adult dose. If you are unsure, ask a pharmacist before taking more. People who drink alcohol regularly or have liver disease should get clinician advice first.
Related Calculators
- Ibuprofen Dosage Calculator — weight-based mg/kg dosing for the other common children's fever medicine.
- Dosage by Weight Calculator — general milligram-per-kilogram dosing helper for other oral medicines.
- Medication Dosage Calculator — convert a prescribed mg/kg dose into tablets or liquid volume.
- Child BMI Calculator — check a child's growth percentile, useful context when weighing them for dosing.
- Baby Weight Percentile Calculator — track how an infant's weight compares with the growth charts.
Disclaimer
Medical disclaimer. This acetaminophen dosage calculator is provided for informational purposes only and is not medical advice, nor a substitute for professional medical advice, diagnosis, or treatment. It estimates a weight-based range and a liquid volume from the inputs you enter; it does not replace the judgment of a pediatrician, pharmacist, or the dosing instructions on your specific product label. Always read the label carefully, use the oral syringe supplied with the medicine, and confirm the correct dose with a qualified healthcare professional before giving medication to a child. Never delay seeking professional medical advice because of something you read here. Dosing errors and combination products that already contain acetaminophen can cause serious liver injury — when in doubt, call your pediatrician or a poison control line.