Which expression correctly shows how to calculate drip rate (gtt/min) given volume per time and drop factor?

• A. time x drip factor
• B. (Volume/time) / drip factor
• C. ml/time in MINUTES x drip rate (gtt/ml)
• D. gtt/min = ml/time in MINUTES x drip rate (gtt/ml)

Answer: (D)

The essential idea is converting volume per time into drops per minute using the drop factor. The drop factor (gtt/ml) tells how many drops come from each milliliter, so to get the rate in drops per minute you multiply the volume by the drop factor and divide by the time.

In algebra, drip rate in gtt/min equals (volume in ml × drop factor in gtt/ml) divided by time in minutes. This makes sense unit-wise: ml × (gtt/ml) cancels the ml, leaving gtt/min.

The expression that places gtt/min on the left and shows the right-hand side as ml/time in minutes multiplied by the drop factor matches this: gtt/min = ml/time in minutes × drop factor (gtt/ml). This is the correct way to calculate because it directly translates volume per time into drops per minute using the drop factor. Other forms misapply the operations or omit the necessary left-hand unit, so they don’t consistently yield gtt/min.