IV Drip Rate (gtt/min)
Gravity IV tubing is counted in drops. The drip rate tells you how many drops should fall each minute.
In this lesson
- The drip-rate formula
- What drop factor means and where it comes from
- Why the answer is a whole number of drops
What you're solving for
gtt/min — drops (gtt) per minute.
Volume in milliliters, times drop factor in drops per milliliter, divided by time in minutes, equals drops per minute
What drop factor means
The drop factor is the number of drops that make 1 mL with a specific tubing set. It is printed on the tubing package. Common values in problems are 10, 12, 15, 20, 60 gtt/mL; tubing with 60 gtt/mL is often called microdrip.
Always use the drop factor given in the problem or printed on the actual tubing. Don't assume a value — tubing sets differ.
Whole drops
You can't count part of a drop, so the final gravity drip rate is written as a whole number of drops per minute. Keep the exact value through the calculation and round to the nearest whole drop only at the end.
Worked examples
Example 1: Hours converted to minutes
1,000 mL over 8 hr. Drop factor: 15 gtt/mL.
Step 1: Convert time to minutes (1 hr = 60 min)
8 hr × 60 = 480 min
Step 2: Formula
Volume (mL) × Drop factor (gtt/mL) ÷ Time (min) = gtt/min
Step 3: Calculation
1,000 mL × 15 gtt/mL ÷ 480 min
= 15,000 gtt ÷ 480 min
= 31.25 gtt/min
Step 4: Round to whole drops
31.25 gtt/min → 31 gtt/min
Step 5: Check your units
mL cancels with /mL, leaving gtt ÷ min = gtt/min.
Exact value 31.25 gtt/min, rounded to the nearest whole drop.
Answer: 31 gtt/min
Example 2: Time in minutes
100 mL over 30 min. Drop factor: 20 gtt/mL.
Step 1: Formula
Volume (mL) × Drop factor (gtt/mL) ÷ Time (min) = gtt/min
Step 2: Calculation
100 mL × 20 gtt/mL ÷ 30 min
= 2,000 gtt ÷ 30 min
= ≈ 66.6667 gtt/min
Step 3: Round to whole drops
≈ 66.6667 gtt/min → 67 gtt/min
Step 4: Check your units
mL cancels with /mL, leaving gtt ÷ min = gtt/min.
Answer: 67 gtt/min
Example 3: Microdrip tubing
60 mL over 1 hr. Drop factor: 60 gtt/mL.
Step 1: Convert time to minutes (1 hr = 60 min)
1 hr × 60 = 60 min
Step 2: Formula
Volume (mL) × Drop factor (gtt/mL) ÷ Time (min) = gtt/min
Step 3: Calculation
60 mL × 60 gtt/mL ÷ 60 min
= 3,600 gtt ÷ 60 min
= 60 gtt/min
Step 4: Check your units
mL cancels with /mL, leaving gtt ÷ min = gtt/min.
With 60 gtt/mL tubing, gtt/min equals mL/hr numerically.
Answer: 60 gtt/min
Common mistakes
Forgetting the drop factor
- What goes wrong
- 1,000 mL ÷ 480 min = 2.08 gtt/min
- Why it fails
- That's mL per minute, not drops.
- Correct approach
- 1,000 mL × 15 gtt/mL ÷ 480 min = 31.25 → 31 gtt/min
Using hours instead of minutes
- What goes wrong
- 1,000 × 15 ÷ 8 = 1,875 gtt/min
- Why it fails
- The formula needs time in minutes.
- Correct approach
- 8 hr = 480 min
Rounding in the middle
- What goes wrong
- Rounding 2.08 mL/min to 2, then × 15 = 30 gtt/min
- Why it fails
- Early rounding shifts the final answer.
- Correct approach
- Keep exact values; round once at the end: 31 gtt/min
Quick self-check
500 mL over 5 hr with 10 gtt/mL tubing?
Show the answer
5 hr = 300 min; 500 × 10 ÷ 300 ≈ 16.67 → 17 gtt/min
Calculate and practice
Related lessons
- IV Flow Rate (mL/hr) — Volume ÷ time in hours = mL/hr.
- Infusion Time — Volume ÷ rate, then decimal hours to hours and minutes.
- Rounding & Number Safety in Medication Math — When to round, how to round, and writing numbers safely.
Sources
- Nursing Skills — Math Calculations — Open RN / NCBI Bookshelf
- Clinical Nursing Skills — 11.2 Dosing — OpenStax
Explanations are original Dosage Calcs wording. See all sources and the methodology.
Educational Use & Safety
Educational content only. These lessons teach medication math using fictional values and do not determine an appropriate medication, dose, infusion rate, or treatment for an actual patient.
Educational Use & Safety