Provide the formula to calculate gravity drip rate (drops per minute) for a given volume, time, and drop factor.

• A. Drip rate (gtt/min) = (Volume in mL × Drop factor) ÷ Time in minutes.
• B. Drip rate = Time in minutes ÷ (Volume in mL × Drop factor).
• C. Drip rate = Volume in mL ÷ Time in minutes.
• D. Drip rate = Drop factor ÷ (Volume × Time).

Answer: (A)

Calculating the gravity drip rate in drops per minute relies on volume, time, and the drop factor. The drop factor tells you how many drops make up 1 mL, so you first convert the total volume into drops by multiplying volume (mL) by the drop factor, then you divide by the time (minutes) to get drops per minute. So the correct formula is:

Drip rate (gtt/min) = (Volume in mL × Drop factor) ÷ Time in minutes.

For example, delivering 100 mL over 30 minutes with a drop factor of 20 gtt/mL yields (100 × 20) / 30 = 2000/30 ≈ 66.7 gtt/min.

Other approaches would omit the drop factor, or place time in the numerator, which would not produce the correct units or rate.