Weight-Based Medication Dosage Calculator
Calculate weight-based medication doses for adults and paediatric patients. Enter the patient's weight, the prescribed dose rate in mg/kg, and administration frequency to calculate single-dose and total daily amounts. For reference only — always verify with a pharmacist or physician.
Key Capabilities
Weight-based mg/kg dose arithmetic
Calculates single-dose and total daily dose from patient weight, prescribed dose rate in mg/kg, and frequency — the standard calculation for paediatric dosing and antibiotics with weight-dependent pharmacokinetics.
Full clinical weight range from 1 kg to 200 kg
Accepts patient weight from 1 kg (neonates) through 200 kg (bariatric adults), covering the complete weight range used in hospital paediatric and adult settings.
Reference-only disclaimer on every output
Every calculation is accompanied by a prominent clinical disclaimer. This tool performs arithmetic only and cannot account for renal impairment, hepatic function, drug interactions, or individualised clinical factors.
How to Use
Enter patient weight in kilograms
Input the actual measured body weight. For paediatric patients, use the most recent measured weight — not an estimated or age-based figure.
Enter the dose rate in mg/kg and frequency
Input the mg/kg dose from the prescription or formulary and select the administration frequency such as twice daily or every 8 hours.
Review the calculated doses
Single dose and total daily dose in mg appear below. Always verify these values with a licensed pharmacist or prescriber before administration.
Common Use Cases
- Paediatric nurses checking orders before administrationA paediatric ward nurse who has received a written medication order performs a rapid weight-based dose check before drawing up the drug, catching any prescription errors before they reach the patient.
- Parents verifying children's antibiotic dosesA parent given a prescription for a paediatric antibiotic at 25 mg/kg/day verifies the prescribed volume against their child's weight to confirm the pharmacist has calculated correctly.
- Veterinary students practising dose calculationsVeterinary students practising weight-based drug dosing check textbook worked examples against the calculator and build calculation confidence before clinical rotations begin.
Frequently Asked Questions
What is weight-based dosing?
Weight-based dosing calculates medication doses proportional to body weight (mg/kg). This is standard practice in paediatric medicine and for drugs with narrow therapeutic indices. Adult doses are usually fixed, but weight-based calculation is still used for antimicrobials, anticoagulants, and chemotherapy.
How do I find the mg/kg dose for a drug?
The mg/kg dose is specified on the drug package insert, British National Formulary (BNF), or prescribing information leaflet. Common examples: amoxicillin 25 mg/kg/day in children, paracetamol 15 mg/kg per dose. Always use the prescribed dose from your doctor or pharmacist.
Is this calculator a substitute for a pharmacist?
No. This tool performs basic arithmetic only and cannot account for renal impairment, hepatic function, drug interactions, loading doses, or individualised clinical factors. Always verify calculated doses with a licensed pharmacist or prescribing physician before administration.
Related Tools
Pregnancy Due Date Calculator
Calculate your estimated due date (EDD) by entering the first day of your last menstrual period (LMP). Based on Naegele's rule (LMP + 280 days). Also shows your current pregnancy week and trimester. Free and private.
APGAR Score Calculator
Score a newborn across all 5 APGAR criteria (Appearance, Pulse, Grimace, Activity, Respiration) and instantly calculate the total score with clinical interpretation. Free, private — no sign-up or uploads required.
eGFR Calculator
Calculate your estimated glomerular filtration rate (eGFR) using the 2021 CKD-EPI equation (race-free). Enter serum creatinine, age, and sex to stage kidney function from G1 (normal) to G5 (kidney failure). Free and private.