Pediatric Dosage Calculator: mg/kg Dose, mL of Liquid and Daily Maximum
Work out a child’s dose from weight: any mg/kg/dose or mg/kg/day order, or children’s acetaminophen and ibuprofen with their usual mg/kg ranges, label weight-chart dose, mL of liquid for the bottle’s strength, and per-dose and daily maximums that are never exceeded.
How it works
Per dose = weight (kg) × mg/kg per dose (or weight × mg/kg per day ÷ doses per day) · capped at the maximum single dose · Daily = per dose × doses, with the number of doses limited so the daily maximum is not exceeded · mL per dose = mg ÷ (mg per mL of the liquid) · Acetaminophen: 10–15 mg/kg every 4–6 h, ≤ 5 doses/24 h, ≤ 75 mg/kg/day, ≤ 1,000 mg/dose and 4,000 mg/day · Ibuprofen: 5–10 mg/kg every 6–8 h, ≤ 4 doses/24 h, ≤ 400 mg/dose
Children are dosed by body weight because the same milligram amount has a much larger effect in a small child. A prescription is written either per dose (mg/kg/dose) or per day (mg/kg/day, which is split across the doses). The calculator multiplies the weight by the rate, then applies two ceilings: a maximum single dose, usually the adult dose, so a heavy teenager never gets more than an adult, and a daily maximum, enforced by limiting how many doses fit in 24 hours. For children’s acetaminophen and ibuprofen it uses the published pediatric ranges: acetaminophen 10–15 mg/kg every 4–6 hours with no more than 5 doses a day (at most 75 mg/kg/day, 1,000 mg per dose and 4,000 mg per day), and ibuprofen 5–10 mg/kg every 6–8 hours with no more than 4 doses a day (at most 400 mg per dose). Entries above those ranges are cut back, never raised. It also shows the fixed dose from the weight chart used on US children’s products, which can differ slightly from the mg/kg figure because each band covers a range of weights. Choosing the liquid strength turns the dose into millilitres. The tool does not know about kidney or liver disease, interactions or the specific product, so the prescription and label always take precedence.
Worked example
With the defaults, a 20 kg child with an order of 15 mg/kg per dose, 4 doses a day and a 1,000 mg single-dose ceiling: 20 × 15 = 300.0 mg per dose, below the ceiling, so 300.0 mg × 4 = 1,200.0 mg/day. Choosing 160 mg/5 mL liquid (32 mg/mL) gives 300 ÷ 32 = 9.38 mL per dose. As children’s acetaminophen the same child (44 lb) is in the 36–47 lb chart band of 240 mg (7.5 mL), and the usual range is 200–300 mg per dose, up to 5 doses in 24 hours.
Sources: Children’s Healthcare of Atlanta: acetaminophen and ibuprofen dose chart (weight bands, liquid volumes, dose limits) · AboutKidsHealth (SickKids): acetaminophen 10–15 mg/kg/dose and ibuprofen 5–10 mg/kg/dose recommendations · StatPearls: acetaminophen dosing (75 mg/kg/day in children; 1,000 mg/dose and 4,000 mg/day in adults) · HealthyChildren.org (AAP): acetaminophen for fever and pain · HealthyChildren.org (AAP): ibuprofen for fever and pain · Omni Calculator: pediatric dose calculator (mg/kg/dose and mg/kg/day with concentration)
Frequently asked questions
How do I calculate a child’s dose in mg/kg?
Multiply the child’s weight in kilograms by the prescribed mg/kg. A 20 kg child at 15 mg/kg needs 300 mg per dose. If the order is in mg/kg per day, divide that total by the number of doses: 40 mg/kg/day for a 20 kg child given 4 times a day is 800 mg ÷ 4 = 200 mg per dose. To convert pounds to kilograms, divide by 2.2046.
How many mL of children’s Tylenol or Motrin should I give?
Divide the dose in mg by the strength of the liquid. Children’s acetaminophen is 160 mg per 5 mL (32 mg/mL), so 240 mg is 7.5 mL. Children’s ibuprofen is 100 mg per 5 mL (20 mg/mL), so 150 mg is 7.5 mL. Infant ibuprofen drops are 50 mg per 1.25 mL, so check the bottle before measuring.
How often can I give acetaminophen or ibuprofen to a child?
Acetaminophen every 4 to 6 hours, no more than 5 doses in 24 hours. Ibuprofen every 6 to 8 hours, no more than 4 doses in 24 hours, and not under 6 months of age unless a doctor advises it. The AAP advises asking a doctor before giving acetaminophen to a child under 2.
Why cap at the adult dose?
Weight-based dosing assumes the child is smaller than an adult. Once weight × rate exceeds the usual adult dose, the adult maximum takes over, otherwise a large adolescent could be given more than an adult would ever receive.
Should I dose by weight or by age?
Weight is more reliable than age because children of the same age vary widely in size. Age bands on packaging are a fallback when the weight is unknown. Use an accurate, recent weight whenever you can.
What about Clark’s rule or Young’s rule?
Those old rules scale an adult dose by weight (Clark: weight in lb ÷ 150) or by age (Young: age ÷ (age + 12)). They are rough and are not used for prescribing today; mg/kg dosing from the drug’s pediatric labeling is the standard.
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Educational estimate only — not medical advice, and not a substitute for a clinician, pharmacist or product label. Dosing, fluid and kidney decisions must be confirmed by a qualified professional using the actual drug, patient and situation. Do not use this tool to self-treat. Check the concentration printed on the bottle every time, measure liquids with the syringe or cup that comes with the medicine, and never give two products that contain the same ingredient.