How to Calculate IV Drip Rate in gtt/min

A gravity IV (one without a pump) is set by counting drops in the drip chamber. The drop factor on the tubing package says how many drops (gtt) make 1 mL: 10, 15 or 20 for macrodrip sets, and 60 for microdrip.

For learning only, not for patient care. With a real patient, always follow the order, the drug’s label and your facility’s policies, and double-check every dose with a pharmacist or a second nurse.

Try it with your own problem ↓

The steps

Read the volume (mL), the time and the drop factor (gtt/mL).
Change the time to minutes: hours × 60.
gtt/min = volume (mL) × drop factor (gtt/mL) ÷ time (min).
Round to a whole drop: you can’t count part of a drop.
Check with the shortcut: mL/hr ÷ (60 ÷ drop factor).

A worked example

Infuse 1,000 mL over 8 hours using tubing with a drop factor of 10 gtt/mL. Find the drip rate.

Time in minutes: 8 × 60 = 480 min.
Multiply the volume by the drop factor: 1,000 × 10 = 10,000 drops.
Divide by the minutes: 10,000 ÷ 480 ≈ 20.83 gtt/min.
Round to a whole drop: 21 gtt/min.
Check: 1,000 ÷ 8 = 125 mL/hr and 60 ÷ 10 = 6, so 125 ÷ 6 ≈ 20.83. ✓

Set the roller clamp to about 21 gtt/min.

Why it works

Each mL is a fixed number of drops, so multiplying the volume by the drop factor counts every drop that has to fall: 10,000 here. Spreading those drops evenly over 480 minutes gives the drops for each minute. The units show it too: mL × gtt/mL ÷ min leaves gtt/min.

Try it with your own problem

Open The Dose Calculator (free) with this example already filled in. It shows every step, and you can type over it with your own numbers.

Work it out: 1000 mL over 8 hours, 10 gtt/mLOpens The Dose Calculator with this example

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More nursing math, every step written out: open The Dose Calculator.

Common mistakes

Leaving the time in hours. The answer is drops per minute, so the time must be in minutes.
Using the wrong drop factor. Take it from the tubing package. With microdrip (60 gtt/mL) the answer equals the mL/hr.
Keeping the decimal. You count whole drops, so 20.83 becomes 21.
Not recounting. Count for 15 seconds and multiply by 4, then recount for a full minute.

Questions people ask

What is the drip rate for 500 mL over 4 hours with a drop factor of 15?

4 hours is 240 minutes, and 500 × 15 ÷ 240 = 31.25, so 31 gtt/min.

Why does microdrip tubing give the same number as mL/hr?

With 60 drops per mL, gtt/min = mL/hr × 60 ÷ 60. The two 60s cancel, so 50 mL/hr is 50 gtt/min.

How many drops should I see in 15 seconds?

Divide the rate by 4. For 21 gtt/min, about 5 drops in 15 seconds.

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