Clinical Medical Calculator
Dosage, Infusion, and Drip Rate Tools for Healthcare Professionals
1. Drug Dosage Calculator (Desired/Have)
2. IV Infusion Rate (mL/hr)
3. IV Drip Rate (gtt/min)
Understanding Medical Calculations in Nursing and Medicine
Medical dosage calculations are a fundamental skill for nurses, paramedics, and physicians. Accurate calculations ensure patient safety and the effective delivery of therapeutic interventions. This med calculator covers the three most common mathematical requirements in a clinical setting: standard dosage, hourly infusion rates, and gravity-fed drip rates.
1. The "Desired Over Have" Formula
The most common calculation used for tablets and liquid medications is the Desired/Have × Volume formula. This is used when you know the dose ordered by the physician and the concentration available in the pharmacy stock.
- Desired: The dose ordered (e.g., 500mg).
- Have: The dosage strength on the label (e.g., 250mg).
- Volume: The form the drug comes in (e.g., 1 tablet or 5mL liquid).
Example: Order: 750mg of Amoxicillin. Stock: 250mg/5mL. Calculation: (750 / 250) * 5 = 15mL.
2. IV Infusion Rates (mL/hr)
When using an infusion pump, the machine requires a rate in milliliters per hour (mL/hr). The math is straightforward: divide the total volume to be infused by the total time in hours.
| Volume (mL) | Time (hrs) | Rate (mL/hr) |
|---|---|---|
| 1000 mL | 12 Hours | 83.3 mL/hr |
| 500 mL | 4 Hours | 125 mL/hr |
| 100 mL | 0.5 Hours (30 min) | 200 mL/hr |
3. Calculating IV Drip Rates (gtt/min)
In settings without electronic pumps, gravity tubing is used. You must calculate the drops per minute (gtt/min) based on the "Drop Factor" of the tubing. The drop factor is the number of drops it takes to make 1 mL (usually 10, 15, or 20 for macro-drip and 60 for micro-drip).
Formula: (Total Volume in mL × Drop Factor) / Time in Minutes = Drops per Minute.
Best Practices for Medical Math
To minimize medication errors, healthcare professionals should always:
- Ensure all units of measurement are the same (convert grams to milligrams if necessary).
- Use leading zeros (0.5 mg, NOT .5 mg).
- Never use trailing zeros (5 mg, NOT 5.0 mg).
- Perform a "sanity check": Does the resulting volume or tablet count seem reasonable?