Which formula is used to calculate drops per minute for an IV infusion when given total volume, drop factor, and infusion time in minutes?

Which formula is used to calculate drops per minute for an IV infusion when given total volume, drop factor, and infusion time in minutes?

• A. Total volume × drop factor ÷ time in minutes
• B. Total volume ÷ drop factor ÷ time in minutes
• C. Time × drop factor ÷ total volume
• D. Volume ÷ drop factor

Answer: (A)

To deliver an IV at a specific drop rate, you first convert the total volume into drops using the drop factor, then divide by the infusion time to get drops per minute. The drop factor is how many drops make up one milliliter, so multiplying the volume in mL by the drop factor gives the total number of drops to be infused. Dividing that by the infusion time in minutes yields the rate in drops per minute. That makes total volume × drop factor ÷ time in minutes the correct formula. For example, 1000 mL with a drop factor of 15 gtt/mL over 120 minutes gives (1000 × 15) / 120 = 125 gtt/min. The other patterns don’t properly convert volume to drops or mix the units in a way that won’t produce a rate in drops per minute.

To deliver an IV at a specific drop rate, you first convert the total volume into drops using the drop factor, then divide by the infusion time to get drops per minute. The drop factor is how many drops make up one milliliter, so multiplying the volume in mL by the drop factor gives the total number of drops to be infused. Dividing that by the infusion time in minutes yields the rate in drops per minute. That makes total volume × drop factor ÷ time in minutes the correct formula. For example, 1000 mL with a drop factor of 15 gtt/mL over 120 minutes gives (1000 × 15) / 120 = 125 gtt/min. The other patterns don’t properly convert volume to drops or mix the units in a way that won’t produce a rate in drops per minute.