Calculate medication dosages using weight-based, BSA-based, or concentration-based methods with pediatric presets, max dose caps, and volume conversions.
Accurate medication dosing is one of the most important aspects of safe prescribing, especially for pediatric patients where every dose is individualized by body weight. This general medication dosage calculator supports the three most common dosing methods used in clinical practice: weight-based dosing (mg/kg), body surface area dosing (mg/m²), and concentration-based dosing (mg/mL for liquid formulations).
Weight-based dosing is the most common method for pediatric medications, where the prescribed dose is calculated as milligrams per kilogram of body weight per dose. BSA-based dosing is used for chemotherapy agents, some biologics, and certain cardiac medications where drug distribution correlates more closely with body surface area than weight alone. Concentration-based calculations help convert a milligram dose into the correct volume of a liquid medication, critical for infant and pediatric prescriptions.
This calculator includes quick presets for commonly prescribed medications like amoxicillin, azithromycin, ibuprofen, and acetaminophen — pre-loaded with their standard mg/kg doses, frequencies, and maximum dose caps. It automatically applies dose ceilings to prevent exceeding FDA-approved maximum doses, calculates total daily and course doses for the specified treatment duration, and converts doses to liquid volumes when a formulation concentration is provided. Use it as a clinical reference tool alongside standard drug references and pharmacist verification.
Manual dose calculations are the leading source of medication errors in pediatric care. This calculator reduces math errors by automating the weight-to-dose conversion, applying maximum dose limits, and converting to liquid volumes — the three steps where most calculation mistakes occur. Common presets for frequently prescribed medications speed up clinical workflow while maintaining accuracy.
Weight-based: Single dose (mg) = weight (kg) × dose (mg/kg). BSA (Mosteller): BSA (m²) = √(weight (kg) × height (cm) / 3600). BSA-based: Single dose = BSA × dose (mg/m²). Volume: Volume (mL) = dose (mg) ÷ concentration (mg/mL). Daily dose = single dose × frequency. Total course = daily dose × days.
Result: 200 mg (10 mL) three times daily = 600 mg/day
A 20 kg child receiving ibuprofen at 10 mg/kg TID: 20 × 10 = 200 mg per dose (under the 400 mg cap). Using 100 mg/5 mL suspension: 200 ÷ 20 = 10 mL per dose. Daily total: 200 × 3 = 600 mg/day.
Weight-based dosing (mg/kg) is the most universal method, used for antibiotics, analgesics, anticonvulsants, and most routine medications. The mg/kg value is determined from clinical trials and represents the dose shown to be safe and effective for a given indication. BSA-based dosing (mg/m²) is mathematically more complex but better accounts for differences in metabolic rate and organ function across patients of different sizes, making it essential for cytotoxic chemotherapy and certain immunotherapies.
The most frequent errors in medication dosing include: (1) weight confusion between kg and lb, causing 2.2× overdoses; (2) forgetting to apply dose caps, leading to adult-range doses in larger children; (3) confusion between "per dose" and "per day" amounts; (4) misreading liquid concentrations (125 mg/5 mL vs 250 mg/5 mL); and (5) decimal point errors. This calculator mitigates these risks by accepting weight in either unit, clearly separating per-dose from per-day totals, applying maximum dose limits, and computing exact volumes.
Drug dosing is not purely mathematical — individual variation in absorption, distribution, metabolism, and excretion means that calculated doses are starting points. Renal and hepatic impairment, drug interactions, genetic polymorphisms, and disease severity all influence the final dose. Always monitor clinical response and drug levels when available, particularly for medications with narrow therapeutic windows like aminoglycosides, vancomycin, and anti-epileptic drugs.
Weight-based dosing calculates the medication dose proportional to the patient's body weight, typically expressed as mg/kg. It ensures that smaller patients receive appropriately lower doses and is the standard method for pediatric prescribing.
BSA-based dosing is preferred for chemotherapy agents, some immunosuppressants, and certain cardiac medications. BSA correlates better with blood volume and drug clearance than weight alone, especially in patients at extremes of body composition.
A dose cap is the maximum amount that should be given in a single administration, regardless of what the weight-based calculation yields. For example, ibuprofen is dosed at 10 mg/kg but capped at 400 mg per dose for children.
Divide the dose in mg by the concentration expressed as mg/mL. If the label says "125 mg/5 mL," first convert to mg/mL (25 mg/mL), then divide: dose(mg) ÷ 25 = volume in mL. Our calculator handles this conversion automatically.
The Mosteller formula is BSA (m²) = √(weight in kg × height in cm ÷ 3600). It is the most commonly used BSA formula in clinical practice due to its simplicity and accuracy.
This depends on the medication. Some drugs (aminoglycosides, heparin) use adjusted body weight. Lipophilic drugs may use actual weight. Check drug-specific references for obese patient dosing.