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IV Drip Rate Lab
Learn the method, check your arithmetic, then drill it. Below you will find the three formulas that cover almost every infusion, the 60-minute clock method that makes gravity drips mental arithmetic, worked examples from a simple bag of saline to a weight-based dopamine infusion, a calculator for when you want the numbers checked, and unlimited practice questions with full solutions.
How drip rates actually work
Three calculations cover almost everything you will meet. Learn the process once and the numbers stop mattering, because every problem is the same shape: how much volume, over how much time, through what equipment.
1. Gravity drip
Drops per minute
No pump. You are counting drops in the chamber, so the tubing’s drop factor decides how many drops make a millilitre. It is printed on the bag of the giving set.
gtt/min = (volume mL x drop factor) / time in minutes
2. Pump rate
Millilitres per hour
A pump asks for mL/h and does the rest. The tubing no longer matters to the maths, only the volume and the time.
mL/h = volume mL / time in hours
3. Weight based
mcg/kg/min to mL/h
Pressors and inotropes are ordered by patient weight per minute, but the pump wants volume per hour. The 60 in this formula is the clock: minutes into an hour.
mL/h = (dose x weight x 60) / concentration mcg/mL
The 60-minute clock
Every drip calculation is an hour cut into pieces. Picture the clock face: one hour, four quarters of 15 minutes. The drop factor tells you how many pieces to cut the hour into, and that number is all you need.
Divide 60 minutes by the drop factor and you get a fixed divisor. Take the hourly rate, divide by that number, and you have drops per minute. No multiplying, no calculator.
divisor = 60 / drop factor then gtt/min = (mL/h) / divisor
| Drop factor | Divide mL/h by | Set |
|---|---|---|
| 10 gtt/mL | 6 | Common macrodrip set |
| 15 gtt/mL | 4 | Macrodrip: the true quarter-hour set |
| 20 gtt/mL | 3 | Macrodrip |
| 60 gtt/mL | 1 | Microdrip: gtt/min equals mL/h exactly |
The 15 gtt/mL set is where the clock is most obvious. 60 divided by 15 is 4, so you divide the hourly rate by 4, which means your drops per minute is simply the volume you would deliver in one quarter of the clock. Running 120 mL/h? That is 30 mL every 15 minutes, so 30 drops a minute. The microdrip set is simpler still: 60 divided by 60 is 1, so gtt/min and mL/h are the same number.
Worked examples
Simple drug
1,000 mL normal saline over 8 hours, 15 gtt/mL set
- Get the hourly rate first. 1,000 mL divided by 8 hours is 125 mL/h. If a pump is running, you are already done.
- Find the divisor for the tubing. 60 divided by 15 is 4.
- Divide the hourly rate by it. 125 divided by 4 is 31 gtt/min.
- Sanity check on the clock: 31 drops a minute means about 31 mL every quarter hour, which is 125 mL in the hour. It agrees, so the answer is sound.
Complex drug
Dopamine 400 mg in 250 mL, 80 kg patient, ordered at 5 mcg/kg/min
- Work out the concentration in mcg/mL. 400 mg is 400,000 mcg, divided by 250 mL is 1,600 mcg/mL.
- Work out the dose per minute. 5 mcg/kg/min times 80 kg is 400 mcg/min.
- Convert dose to volume. 400 mcg needed, divided by 1,600 mcg in every mL, is 0.25 mL/min.
- Put it on the clock. 0.25 mL every minute times 60 minutes is 15 mL/h. That is the pump rate.
Norepinephrine 4 mg in 250 mL runs the same way: 4,000 mcg over 250 mL is 16 mcg/mL, so a 70 kg patient at 0.1 mcg/kg/min needs 7 mcg/min, which is 0.44 mL/min, or about 26 mL/h.
Read this before you use any of it
These are teaching examples with textbook concentrations. Real mixes, ordered dose ranges, and who may run an infusion at all vary by service and province. Always confirm the concentration on the bag in front of you, follow your own protocols and medical direction, and have a second person check high-risk infusions where your service requires it.
Drip rate calculator
For when you know the method but want the arithmetic checked. Every answer shows its own working, so you can see where the numbers came from rather than trusting a box.
What are you calculating?
Pick one:
How much fluid is going in, from the bag or the order.
How long it should take. Half an hour is 0.5.
Printed on the giving set’s packaging. Only needed for a gravity drip.
Pump rate
125 mL/h
Gravity drip at 15 gtt/mL
31 gtt/min
Working
- mL/h = volume / time = 1,000 / 8 = 125 mL/h
- gtt/min = mL/h / (60 / 15) = 125 / 4 = 31 gtt/min
Check the answer against the bag and the order before anything runs. This is a study tool, not a prescribing or dose-verification device, and it does not know your protocols or your patient.
Practice questions
Unlimited generated problems across all three calculation types. Every answer reveals the worked solution, so a wrong one teaches as much as a right one.
Pick a practice type:
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A free study aid from Delta Emergency Support Training. This is not certification and not medical direction. The concentrations shown are common textbook mixes for practice; real mixes, doses, and infusion authority vary by service and province. Always follow your own protocols, medical oversight, and pump programming procedures.