Dosage Calculator

Calculate weight-based drug dosages. Enter dose per kg, patient weight, and frequency to see per-dose and daily totals with optional liquid volume.

Calculator

Disclaimer: This tool is for educational purposes only. It does not constitute medical advice. Always consult your doctor or pharmacist before administering any medication.

Presets:

Dose (mg/kg)

Set to 0 for flat-dose drugs

Patient Weight

Frequency (times per day)

1x = QD, 2x = BID, 3x = TID, 4x = QID

Concentration (mg/mL) — optional

For liquid formulations — calculates volume per dose

Per Dose

Daily Total

Volume per Dose

Patient Weight

Parameter	Value
Dose per kg
Patient weight
Frequency
Single dose
Daily total
Volume per dose

How to Use

1
Enter dose and weight
Input the prescribed dose in mg/kg and the patient's body weight in kilograms or pounds.
2
Set frequency
Select the dosing frequency: once, twice, three, or four times per day.
3
Read results
View the calculated per-dose amount (mg), daily total (mg), and optional liquid volume (mL) if a concentration is provided.

About

Weight-based dosing is the cornerstone of individualized pharmacotherapy. The amount of drug required to achieve a target plasma concentration is proportional to the volume of distribution, which correlates with body mass. By expressing the dose as milligrams per kilogram (mg/kg), clinicians normalize for the largest single variable affecting drug exposure across patients.

Liquid formulations add a practical dimension: converting milligrams to milliliters using the concentration (mg/mL) printed on the suspension bottle. Errors in this conversion are a leading cause of pediatric medication errors, which is why automated calculation is valuable as a cross-check.

Important limitations include: this calculator does not account for renal or hepatic impairment, obesity-related dosing adjustments, drug interactions, or patient-specific factors like pregnancy or pharmacogenomics. These factors require clinical judgment by a qualified healthcare professional.

FAQ

What is weight-based dosing?

Weight-based dosing calculates the drug amount proportional to a patient's body weight, expressed as mg/kg. This method accounts for differences in body size and is standard in pediatrics and for drugs with a narrow therapeutic index.

What is the difference between mg/kg dosing and a flat dose?

Mg/kg dosing scales the drug amount to body weight, ensuring appropriate plasma concentrations regardless of patient size. Flat dosing gives every patient the same milligram amount and is used when body weight has minimal impact on pharmacokinetics, such as with metformin 500 mg.

Why is pediatric dosing different from adult dosing?

Children have higher metabolic rates per kilogram, different body-water ratios, and immature hepatic enzyme systems. Weight-based calculations prevent both underdosing (therapeutic failure) and overdosing (toxicity) in pediatric patients.

How does renal impairment affect drug dosing?

Reduced kidney function slows the clearance of renally excreted drugs, leading to accumulation. Clinicians use creatinine clearance (CrCl) or estimated GFR to adjust doses downward or extend dosing intervals to maintain safe plasma levels.

What is a maximum dose and why does it matter?

A maximum dose is the upper safety limit regardless of body weight. For example, acetaminophen should not exceed 4,000 mg/day in adults. Even if the mg/kg calculation yields a higher number, the maximum dose caps the amount to prevent organ toxicity.

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This content is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making medication decisions.

Data sources: ChEMBL, PubChem, DailyMed.