# Help with this calculation please for gtt/min

Published

• Has 5 years experience.

It's for calculating the flow rate in gtt/min

Order: IV D5 1/3 NS, infuse at 40 mL/h. What is the rate in microdrops per minute?

I used the formula of x gtt/min = (amount of solution)(drop factor) / time in minutes.

So my calculation was: (40mL/h)(60) / 1 = 2400 gtt/min.

But the answer in the back of the book says it's 40 gtt/min. You can get 40 if you divide by 60 instead of 1...

But in another problem: Order infuse 100 mL of 0.9% NS over 30 min. Calculate using microdrip.

I did: (100)(60)/30 = 200 gtt/min and that answer is correct in the book.

If anyone can please explain this I'd appreciate it, I'm sure I'm overthinking..

1,334 Posts

Specializes in NICU.

Your calculation of 40mL/hr x 60gtt/mL / 1 = 2400 is correct, but that is 2400 gtt per hour, you have to divide by 60 to convert to gtt per minute.

1 Article; 327 Posts

Order: IV D5 1/3 NS, infuse at 40 mL/h. What is the rate in microdrops per minute?

I used the formula of x gtt/min = (amount of solution)(drop factor) / time in minutes.

So my calculation was: (40mL/h)(60) / 1 = 2400 gtt/min.

I hope someone corrects me if I'm wrong...

But if you're infusing 40 mL in 1 hour, you would divide the 40 x 60 by 60 minutes (or 1 hour). So it'd be (40)(60)/60. The second one is infusing over 30 minutes so you'd be dividing by 30 minutes instead of 60. In the first problem you divided by 1. It looks like you divided in the measure of 1 hour rather than 60 minutes.

1,069 Posts

Has 5 years experience.

Aha, thank you very much KRVRN, BSN!! That's a good reminder for me too to stop dropping the "mL/hr" when I do calculations, and write everything out not just the numbers.

1,069 Posts

Has 5 years experience.

Thank you Augurey!

I hope someone corrects me if I'm wrong...

But if you're infusing 40 mL in 1 hour, you would divide the 40 x 60 by 60 minutes (or 1 hour). So it'd be (40)(60)/60. The second one is infusing over 30 minutes so you'd be dividing by 30 minutes instead of 60. In the first problem you divided by 1. It looks like you divided in the measure of 1 hour rather than 60 minutes.

6 Articles; 11,345 Posts

Specializes in OR, Nursing Professional Development. Has 18 years experience.

You can also kind of get a quick check when you look at your answers- there's no realistic way to count 2,400 gtts/min. When you do a drug calculation, if you get big numbers like that or really tiny numbers, you've likely missed a conversion factor/step in your equation.

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