Clinical Calculator
Dosage Calculator
Calculate drug dosage by body weight (mg/kg), volume to administer, and pediatric dose checks. For clinicians, nurses, and pharmacists.
Weight (kg)
—
kg
Single Dose
—
mg / dose
Daily Dose
—
mg / day
Weekly Dose
—
mg / week
Calculate the volume to draw up or administer based on dose and drug concentration.
Calculated Dose
—
mg
Dose to Give
—
mg (after cap)
Volume to Give
—
mL
Verify pediatric dosing against adult maximum dose limits.
Calculated Dose
—
mg
Max Adult Dose
—
mg
% of Adult Max
—
%
Formulas
Mode A — Basic mg/kg Dose
Dose (mg) = Weight (kg) × Dose per kg (mg/kg)
Daily dose = Single dose × Frequency (doses/day)
Weekly dose = Daily dose × 7
If weight in lbs: kg = lbs / 2.2046
Weekly dose = Daily dose × 7
If weight in lbs: kg = lbs / 2.2046
Mode B — Volume to Administer
Volume (mL) = Dose (mg) / Concentration (mg/mL)
If max dose set: Dose to give = min(Calculated dose, Max dose)
Volume reflects the capped dose
Volume reflects the capped dose
Mode C — Pediatric Dose Check
Ped. dose = Weight (kg) × Dose (mg/kg)
% of adult max = (Ped. dose / Max adult dose) × 100
Flag if calculated dose exceeds max adult dose
Flag if calculated dose exceeds max adult dose
How to Use This Calculator
1
Select your calculation mode: mg/kg Dose for total dose from weight, Volume to Give to find how many mL to draw up, or Pediatric Check to verify dose against adult maximum.
2
Enter the patient's weight in kg or lbs — the calculator converts lbs to kg automatically (÷ 2.2046).
3
Enter the prescribed dose in mg/kg as ordered by the prescriber.
4
Click Calculate to get the total dose in mg, daily dose, weekly dose, and volume if applicable.
Worked Example
Amoxicillin for a child: 25 mg/kg/dose, 20 kg patient, 3 times daily
Single dose = 25 × 20 = 500 mg per dose
Daily dose = 500 × 3 = 1,500 mg/day
Volume to give: Amoxicillin 250 mg/5 mL suspension = 50 mg/mL
Volume = 500 mg / 50 mg/mL = 10 mL per dose
Frequently Asked Questions
mg/kg dosing is weight-based dosing where the drug amount is calculated per kilogram of body weight. For example, a dose of 25 mg/kg for a 20 kg patient = 500 mg. This approach ensures the correct drug exposure relative to patient size.
Divide weight in pounds by 2.2046. For example, 154 lbs ÷ 2.2046 = 69.9 kg ≈ 70 kg. This calculator performs the conversion automatically when you select lbs.
Children have different body composition, metabolic rates, and organ maturity compared to adults. Weight-based dosing ensures drug exposure is appropriate relative to body size, reducing the risk of under-dosing (treatment failure) or over-dosing (toxicity).
A loading dose is a higher initial dose administered to rapidly achieve therapeutic drug concentrations in the body. It is followed by lower maintenance doses to sustain those levels. Loading doses are used for drugs with long half-lives or when rapid therapeutic effect is needed (e.g., phenytoin, vancomycin, digoxin).
Volume (mL) = Dose (mg) / Concentration (mg/mL). For example, if you need 500 mg and the drug is available at 50 mg/mL: Volume = 500 / 50 = 10 mL. Use the Volume to Give mode in this calculator.
Per dose refers to a single administration amount. Per day is the total drug given across all doses in 24 hours. For example, amoxicillin 500 mg per dose given 3 times daily = 1,500 mg per day. This distinction matters for assessing total drug exposure and adherence to prescribing limits.