Dosage Calculator
Calculate medication dosage based on patient weight using mg/kg dosing. Essential for pediatric and weight-based drug dosing.
About This Calculator
How to Use
- Select the weight unit (kg or lb)
- Enter the patient's weight
- Enter the dose in mg/kg from prescribing information
- Select the dosing frequency
- Optionally enter a maximum single dose if applicable
- Optionally enter drug concentration for liquid volume calculation
- Click Calculate to see results
📚 Understanding Weight-Based Dosing
Weight-based dosing (mg/kg) calculates medication doses proportional to a patient's body weight. This approach is standard in pediatrics and for many adult medications, ensuring appropriate drug levels based on body size.
The basic formula is: Dose (mg) = Weight (kg) x Dose (mg/kg)
For liquid medications, volume is calculated as: Volume (mL) = Dose (mg) / Concentration (mg/mL)
🧮 Dosing Calculations
Single Dose (mg) = Patient Weight (kg) x Dose (mg/kg)
Daily Dose (mg) = Single Dose x Doses per Day
Volume (mL) = Single Dose (mg) / Concentration (mg/mL)
Example: A 25 kg child prescribed amoxicillin 25 mg/kg/day divided TID:
Daily dose = 25 kg x 25 mg/kg = 625 mg/day
Single dose = 625 mg / 3 = 208.3 mg per dose
If suspension is 250 mg/5mL: Volume = 208.3 / 50 = 4.2 mL per dose
📋 Common Dosing Abbreviations
| Abbreviation | Meaning | Doses/Day |
|---|---|---|
| QD | Once daily | 1 |
| BID | Twice daily | 2 |
| TID | Three times daily | 3 |
| QID | Four times daily | 4 |
| Q4H | Every 4 hours | 6 |
| Q6H | Every 6 hours | 4 |
| Q8H | Every 8 hours | 3 |
💡 Practical Use Cases
- Pediatric Dosing: Calculate appropriate doses for children based on weight
- Antibiotic Dosing: Many antibiotics are dosed per kg body weight
- Analgesic Dosing: Calculate pain medication doses safely
- Liquid Medications: Determine volume to dispense for suspensions/solutions
- Dose Verification: Double-check prescribed doses against weight-based recommendations
- Emergency Medications: Quick calculations for weight-based emergency drugs
❓ Frequently Asked Questions
What if the calculated dose exceeds the maximum?
When a calculated dose exceeds the maximum single dose limit, the calculator will cap the dose at the maximum and display a warning. This is common when adult maximum doses apply to larger pediatric patients or adults.
Should I use actual or ideal body weight?
This depends on the medication. Most drugs use actual body weight, but some (like aminoglycosides in obese patients) may use ideal or adjusted body weight. Always consult drug-specific prescribing information.
How do I convert mg/kg/day to a single dose?
First calculate total daily dose (weight x mg/kg/day), then divide by the number of doses per day. For example, 30 mg/kg/day divided TID means each dose is (weight x 30) / 3 mg.
Is this calculator safe for neonatal dosing?
While the calculator performs accurate math, neonatal dosing requires specialized knowledge of gestational age, renal/hepatic function, and drug-specific considerations. Always use neonatal-specific references and consult a pharmacist.