Paracetamol — the drug known as acetaminophen in the United States and Tylenol as a brand name — is the most widely used pain and fever medicine in the world. It is also one of the most common causes of accidental overdose, because "a couple more tablets" quickly exceeds the safe daily limit. This paracetamol dosage calculator converts the patient's body weight into a precise milligram dose, tells you how many 500 mg tablets that equals, and flags the safe maximum for a 24-hour period.
The clinical rule is simple: give 15 mg per kilogram of body weight for each dose, wait at least 4-6 hours before the next one, and never exceed 4 doses in 24 hours. For a 20 kg child that is 300 mg per dose, or 1200 mg across the whole day. Adults and larger people are capped at 1000 mg per dose and 4000 mg in 24 hours, whichever comes first. Adjust the sliders below and every figure updates instantly.
How to Use
- Enter the Patient's Weight in kilograms. Dosing is weight-based, not age-based, so an 8-year-old who weighs 35 kg needs a bigger dose than a 6-year-old who weighs 20 kg. If you only have pounds, divide by 2.2.
- Set the Tablet / Caplet Strength from the product label. Ordinary tablets are 500 mg; extra-strength caplets are often 1000 mg; infant and child liquids are measured in milligrams per 5 mL instead.
- Choose the Planned Doses per 24 h. The standard answer is 4 (one every 6 hours). You may plan fewer, but the calculator warns if your planned total approaches the ceiling.
- Read the result card: the Single Dose (mg), the Tablets per Dose, the minimum interval, the safe 24-hour maximum, and your planned daily total.
If the calculated dose lands between two tablet sizes, round down to the nearest half tablet rather than splitting a dose upward. Always double-check the concentration on the bottle — infant drops and child suspension are not interchangeable, and using the wrong one is the single most common dosing mistake parents make.
The 15 mg/kg Rule Explained
Every major guideline — the WHO model formulary, the British National Formulary for Children, and the FDA acetaminophen labeling — converges on the same weight-based figure:
Single dose (mg) = body weight (kg) × 15
Because paracetamol keeps working for roughly 4-6 hours, the dose may be repeated at that interval. Four doses at 15 mg/kg equals 60 mg/kg per day, which is the recognized safe ceiling. Above 50 kg the weight-based line stops climbing and the adult fixed limits take over: 1000 mg per dose and 4000 mg in 24 hours. That is why a 20 kg child gets 300 mg (weight-limited) while a 70 kg adult gets 1000 mg (capped) — the engine takes the smaller of the two.
The 4000 mg figure matters because the liver converts paracetamol into a toxic by-product, NAPQI, that it can only neutralize in small batches. Taking more than 4000 mg in a day — or combining paracetamol with other cold-and-flu products that already contain it — is how otherwise healthy people end up in hospital. Roughly half of acute liver-failure admissions in the US are linked to accidental acetaminophen overdose, which is why the daily cap is stated so prominently on every pack.
Examples
Example 1 — A 20 kg child. Weight 20 kg, standard 500 mg tablet, 4 planned doses. Single dose = 20 × 15 = 300 mg, which is 0.6 tablets — most parents instead use 120 mg/5 mL child liquid, giving 12.5 mL per dose. Safe 24-hour maximum = 20 × 60 = 1200 mg, and 4 doses of 300 mg lands exactly on that ceiling (100% of it), so no extra doses should be added.
Example 2 — A 70 kg adult. Weight 70 kg, 500 mg tablets, 4 planned doses. The weight-based math would give 1050 mg, but the adult ceiling caps the single dose at 1000 mg = 2 tablets, and the 24-hour total is capped at 4000 mg = 8 tablets. The calculator automatically applies the lower number, which is the correct clinical behavior.
Example 3 — A 10 kg toddler. Weight 10 kg, 250 mg infant tablets, 4 doses. Single dose = 10 × 15 = 150 mg = 0.6 tablets, safe daily maximum = 600 mg. This is a good example of why dosing by age fails: a 10 kg one-year-old and a 10 kg three-year-old need the identical dose, even though their ages differ by two years.
FAQ
How much paracetamol can I give per kilogram?
The standard dose is 15 mg for each kilogram of body weight, repeated every 4-6 hours. For a 20 kg child that is 300 mg per dose; for a 30 kg child it is 450 mg. Adults and anyone over about 50 kg are capped at 1000 mg (1 g) per dose regardless of weight.
What is the maximum daily dose of paracetamol?
The safe 24-hour ceiling is 60 mg/kg by weight (for children), which equals 4 doses of 15 mg/kg. For adults the hard limit is 4000 mg (4 g) in any 24-hour period. Taking more — especially across multiple cold remedies that already contain paracetamol — can damage the liver.
How many 500 mg paracetamol tablets is a safe dose?
Most adults take 1-2 tablets (500-1000 mg) per dose, no more than 4 times a day, which is 8 tablets (4000 mg) total. For children, divide the calculated milligram dose by 500 to get the tablet count; it will usually be a fraction, so a liquid formulation is easier and more accurate.
Can I take paracetamol every 4 hours?
You can repeat a dose every 4-6 hours if needed, but at 15 mg/kg the safe upper limit is 4 doses in 24 hours. Dosing every 4 hours around the clock would risk 6 doses and blow past the 60 mg/kg/day ceiling. Space doses at least 6 hours apart when possible, and never wake a sleeping child just to medicate.
Is paracetamol the same as acetaminophen?
Yes. Paracetamol is the international (INN) name, acetaminophen is the United States name, and both refer to the exact same molecule (N-acetyl-p-aminophenol). Brand names include Tylenol, Panadol, and others. The dosing rules in this calculator apply to all of them.
When should I not dose by weight?
Babies under 3 months, people with liver disease, anyone who drinks heavily, and patients already taking warfarin should get dosing guidance from a clinician rather than a calculator. If fever lasts more than 3 days or the patient is under 3 months old, contact a doctor before dosing.
Related Calculators
- Acetaminophen Dosage Calculator — the same molecule under its U.S. name, tuned for liquid mg/5 mL dosing.
- Ibuprofen Dosage Calculator — the other common children's pain and fever medicine, also weight-based.
- 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 — growth context that helps confirm a child's weight before dosing.
Disclaimer
Medical disclaimer. This paracetamol 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 reference dose from published pediatric guidance (WHO model formulary, BNFC, and FDA labeling), but it cannot replace a doctor, pharmacist, or the instructions on your specific product label. Strengths, formulations, and safe limits differ by country and product, and some combination cold-and-flu medicines already contain paracetamol. Always confirm the correct dose with a qualified healthcare professional or a pharmacist, especially for infants, children, pregnant people, and anyone with liver problems. Never delay seeking medical advice because of something you read here. For editorial standards see the About page, and for data handling see the Privacy Policy.