Dosage Calculator
Practice weight-based dosage math. Enter patient weight in kg or lb, the ordered dose in mg/kg, and an optional concentration in mg/mL to get the dose in milligrams and the volume to draw.
Example: with Patient weight 30 · Weight unit kg · Ordered dose (mg/kg) 15 · Concentration (mg/mL, optional) 100 → Dose per administration: 450 mg per dose.
- Volume to draw4.5 mL (at 100 mg/mL)
- The math30 kg × 15 mg/kg = 450 mg
- NoteWeight-based math practice only — not a dosing recommendation.
Computed by the calculator below using its default values. Change any input to see your own numbers.
The classic nursing formula is dose (mg) = weight (kg) × mg/kg ordered; volume = dose ÷ concentration. Pounds convert at 1 lb = 0.45359237 kg.
The weight-based formula, step by step
Most weight-based orders read as milligrams per kilogram. Multiply the patient's weight in kilograms by that number and you have the dose. A 30 kg child at 15 mg/kg is 30 × 15 = 450 mg. If the drug comes as a solution, divide the dose by the concentration to get the volume to draw: 450 mg from a 100 mg/mL vial is 4.5 mL. Weights given in pounds convert first at 1 lb = 0.45359237 kg.
This is the arithmetic taught in nursing programs and med-math courses. What it deliberately does not include is whether the ordered mg/kg is appropriate, the maximum daily dose, or adjustments for kidney or liver function — those come from references, the prescriber, and a pharmacist, not from the multiplication itself.
How it’s calculated
Dose (mg) = weight (kg) × ordered mg/kg. Volume (mL) = dose ÷ concentration (mg/mL). Pounds convert with 1 lb = 0.45359237 kg (exact). Results round to a tenth at or above 100 and to three decimals below.
This checks arithmetic only. It does not know the drug, its safe range, the maximum dose, frequency, or the patient's organ function, so it must never be used to give a real medication. Follow the order, the label, and a pharmacist.
Weight-based dose examples
| Weight | At 10 mg/kg | At 15 mg/kg |
|---|---|---|
| 10 kg | 100 mg | 150 mg |
| 20 kg | 200 mg | 300 mg |
| 30 kg | 300 mg | 450 mg |
| 50 kg | 500 mg | 750 mg |
| 70 kg | 700 mg | 1,050 mg |
Dose = weight (kg) × mg/kg. Illustrative practice values only, not dosing guidance.
Common mistakes
- Skipping the pounds-to-kilograms conversion and dosing on lb — that overshoots by more than double.
- Confusing mg/kg per dose with mg/kg per day, which changes each administration.
- Dividing by the total vial content instead of the concentration when finding volume.
- Trusting the arithmetic as a safe dose without checking the drug's actual limits.
Frequently asked questions
How do I calculate a weight-based dose?
Multiply weight in kilograms by the ordered mg/kg. A 30 kg patient at 15 mg/kg gets 450 mg. Divide by the concentration to find the volume to draw.
How do I convert pounds to kilograms for dosing?
Divide pounds by 2.2046, or multiply by 0.45359237. An 88 lb patient is about 39.9 kg, so at 10 mg/kg the dose is roughly 399 mg.
Is mg/kg per dose or per day?
It depends on the order. Some orders give mg/kg per dose, others give a daily total split into several doses, so always read which one is written.
Can I use this to give a medication?
No. It is math practice. It cannot judge whether a dose is safe or exceeds a maximum. Always confirm real doses with the prescriber, the label, and a pharmacist.