Drug Dosage Calculator
Weight-based medication dosage
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Drug Dosage Calculator turns the numbers behind weight-based medication dosage into a result, step by step. Type Patient Weight (kg), Dose per kg (mg/kg) and Times per Day into Drug Dosage; each keystroke re-runs the math. Drug Dosage prints the result and its working. Anyone comparing options in Health can use Drug Dosage to compare scenarios. Nothing is uploaded while Drug Dosage works, and the figures stay put. Drug Dosage sits in the Health section next to related tools and drug dosage calculator medication dose mg/kg. Keep Drug Dosage bookmarked for next time. No sign-up or email — Drug Dosage answers as you type.
What the defaults give
A 70 kg patient at 10 mg/kg needs 700 mg per dose.
At three doses a day that is 2,100 mg a day. The arithmetic is simple; the clinical judgement behind the numbers is not, which is why this page is education rather than instruction.
The formula
Dose (mg) = weight (kg) × dose per kg (mg/kg), and daily total = dose × doses per day.
70 × 10 = 700 mg; 700 × 3 = 2,100 mg a day.
Worked examples
70 kg at 10 mg/kg, 3×/day → 700 mg per dose, 2,100 mg/day
50 kg at 10 mg/kg, 3×/day → 500 mg per dose, 1,500 mg/day
70 kg at 15 mg/kg, 2×/day → 1,050 mg per dose, 2,100 mg/day
12 kg at 10 mg/kg, 4×/day → 120 mg per dose, 480 mg/day
Why weight-based dosing is not just multiplication
Real prescribing adds caps and adjustments the formula alone does not carry. Many drugs have a maximum single dose or a maximum daily total regardless of weight, so a heavier patient stops scaling once the ceiling is reached. Renal and hepatic impairment often require a reduced dose unrelated to weight. Children are frequently dosed by body surface area rather than kilograms, and some drugs are dosed on ideal or adjusted body weight in obesity rather than actual weight.
What this page does not do
- It does not check maximum doses. A result above the labelled ceiling is still printed.
- It does not know the drug. Concentration, formulation and route change what a milligram means in millilitres.
- It does not adjust for kidney or liver function, age, pregnancy or interactions.
- It does not round to what is available. A calculated 700 mg may correspond to a 500 mg plus 200 mg tablet, or a liquid volume.
Use the number to understand how a published regimen is derived. Confirm any actual dose with a pharmacist or prescriber and the product labelling.
Frequently Asked Questions
How is 700 mg calculated for a 70 kg patient?
70 kg multiplied by 10 mg per kg equals 700 mg per dose. Three doses a day gives 2,100 mg over 24 hours.
Does dose always scale with weight?
No. Many drugs have fixed maximum doses, and renal or hepatic impairment requires reductions that have nothing to do with weight.
Why do children sometimes use body surface area?
Because surface area tracks organ function and metabolic capacity more closely than mass does across a wide range of sizes, particularly in small children.
Should obese patients use actual body weight?
Not always. Some drugs are dosed on ideal or adjusted body weight because the drug does not distribute into fat tissue.
How do I convert milligrams to millilitres?
Divide by the concentration: 700 mg at 250 mg per 5 ml is 14 ml. The concentration must come from the product label, not from this calculator.
Is this a substitute for a prescription?
No. It is arithmetic education. Dosing depends on the specific drug, indication, patient and formulation, and must be confirmed by a qualified prescriber.
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