How is IV infusion rate calculated using drop factor?

• A. Rate (gtt/min) = (Volume (mL) x Drop factor) / Time (min); use an infusion pump when available.
• B. Rate (mL/hr) = Volume / Time.
• C. Rate (gtt/min) = Time / (Volume x Drop factor).
• D. Rate (mL/hr) = Drop factor.

Answer: (A)

When calculating IV infusion rate with a drop factor, you convert the prescribed volume into drops per minute. The number of drops per minute is found by multiplying the volume in milliliters by the drop factor (in drops per milliliter) and then dividing by the time in minutes. So the rate is Rate = (Volume in mL × Drop factor in gtt/mL) ÷ Time in minutes. This gives you drops per minute (gtt/min). Using an infusion pump is best when available, but for gravity infusions this formula ensures you deliver the correct rate.

For example, infusing 1000 mL over 480 minutes (8 hours) with a drop factor of 15 gtt/mL: Rate = (1000 × 15) / 480 ≈ 31 gtt/min.

The other approaches either omit the drop factor, use the wrong units (mL/hr without converting from drops per minute), or invert the relationship (Time divided by Volume × Drop factor), which would not yield a correct drops-per-minute rate.