π Medication Dosage Calculator
Weight-based dose, liquid volume, and tablet math. Confirm with your pharmacist.
INFORMATIONAL ONLY. Never dose medication from a web calculator alone: confirm every dose with your clinician or pharmacist.
Medication math is simple arithmetic with zero tolerance for error: dose equals weight times mg/kg, volume equals dose divided by concentration. This calculator does the arithmetic for weight-based doses, liquid volumes, and tablet counts. It does not prescribe, and every result needs your clinician's or pharmacist's confirmation before any medication is given.
How to Use This Calculator
Enter weight, the prescribed mg/kg dose, and the product concentration. The dose, volume, and tablet count appear.
Enter weight in pounds and the prescribed dose in mg/kg.
Enter the liquid concentration (mg per 5 mL) and/or tablet strength.
Read the dose and volume, then confirm with your pharmacist before administering.
The Formulas
Weight-based dosing exists because drug clearance scales roughly with body size, especially in children, where a fixed adult dose would overdose a toddler and underdose a teen. The mg/kg figure comes from the drug's labeling or your prescriber: this calculator never supplies it. Concentration math is unit discipline: 200 mg per 5 mL is 40 mg/mL, so a 200 mg dose is 5 mL. Most liquid errors are concentration errors, reading the wrong product strength, not arithmetic errors.
The safety checks no calculator performs: maximum single and daily doses (many pediatric drugs cap at the adult dose), renal and hepatic adjustment, drug interactions, allergy history, and whether the mg/kg figure applies to actual, ideal, or adjusted body weight (obesity changes the rules for some drugs). Your pharmacist checks these reflexively; that is the confirmation step this page insists on.
Worked Example
A 44 lb (20.0 kg) child prescribed 10 mg/kg: dose = 20.0 x 10 = 200 mg. Suspension 200 mg/5 mL: volume = 200/40 = 5.0 mL. Clean numbers, one teaspoonful. Now a 66 lb (30 kg) child at the same 10 mg/kg: 300 mg, 7.5 mL of the same suspension. The volume scales linearly with weight, which is the entire logic of pediatric dosing, and why kitchen spoons (which vary wildly) must never substitute for the dosing syringe the pharmacy provides.
Administration Safety
Use the dosing device that comes with the medication: oral syringes for small volumes, dosing cups for larger ones, never kitchen spoons. Shake suspensions before measuring. Double-check the concentration on the bottle every refill: pharmacies sometimes dispense a different strength, and the old volume becomes wrong. For tablets, fractional tablets are often impractical or unsafe with scored vs unscored and extended-release forms: the pharmacist confirms whether splitting is acceptable.
Keep a medication list with doses and schedules, especially for children and older adults on multiple drugs. Store medications up, away, and out of children's reach; pediatric overdoses are overwhelmingly accidental ingestions, not dosing errors. And the standing rule: this page does arithmetic. Prescribing, the choice of drug and mg/kg, belongs to the clinician; dispensing verification belongs to the pharmacist. The calculator sits between them as a double-check, never as the authority.
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For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
How do you calculate mg/kg dosage?
Dose (mg) = weight (kg) x prescribed mg/kg. Example: 20 kg x 10 mg/kg = 200 mg. The mg/kg figure comes from the prescriber or drug labeling; calculators do the arithmetic, never the prescribing.
How do you calculate liquid medication volume?
Volume (mL) = dose (mg) / concentration (mg/mL). Example: 200 mg dose with 200 mg/5 mL suspension (40 mg/mL) = 5 mL. Always verify the concentration printed on your bottle.
Can I use a kitchen spoon for liquid medicine?
No. Kitchen spoons vary from 2.5 to 7+ mL, causing large dosing errors. Use the oral syringe or dosing cup supplied with the medication; pharmacists provide them free on request.
What is the maximum dose for weight-based drugs?
Many pediatric drugs cap at the adult maximum dose regardless of weight. The cap is drug-specific and comes from labeling or the prescriber; calculators do not know it, which is why pharmacist confirmation matters.
Do you use actual or ideal body weight for dosing?
It depends on the drug: most pediatric dosing uses actual weight, but some drugs (especially in obesity) use ideal or adjusted body weight. The prescriber specifies which; do not assume.
How do renal problems affect dosing?
Kidneys clear many drugs, so renal impairment requires dose reduction or longer intervals to avoid accumulation and toxicity. Prescribers adjust using creatinine clearance; this is a key pharmacist verification step.
What should I check before giving a child medication?
The five rights: right patient, right drug, right dose, right time, right route. Plus: concentration on the bottle, expiry date, proper measuring device, and allergy history. When in doubt, call the pharmacist.
Can tablets be split for partial doses?
Only if the pharmacist confirms: scored immediate-release tablets usually can; extended-release, enteric-coated, and capsules usually cannot. Splitting the wrong tablet changes how the drug releases.
How should liquid antibiotics be stored?
Most reconstituted suspensions require refrigeration and expire 10-14 days after mixing; the label states both. Shake well before each dose and measure with the supplied device.
What if I miss a medication dose?
General rule: take it when remembered unless it is nearly time for the next dose; never double up. Specific drugs have specific rules, so the pharmacist's guidance for that medication governs.