IV Flow Rate (mL/hr)
An IV flow rate tells you how many milliliters infuse each hour. It is the rate typically entered on an infusion pump.
In this lesson
- The volume ÷ time formula
- Converting minutes to hours first
- What the mL/hr unit means
What you're solving for
mL/hr — milliliters per one hour.
Volume in milliliters divided by time in hours equals milliliters per hour
The time must be in hours. If it's given in minutes, divide by 60 first (or use the minutes-to-hours conversion).
Worked examples
Example 1: Time in hours
Infuse 1,000 mL over 8 hr.
Step 1: Formula
Volume (mL) ÷ Time (hr) = mL/hr
Step 2: Calculation
1,000 mL ÷ 8 hr
= 125 mL/hr
Answer: 125 mL/hr
Example 2: Time in minutes
Infuse 100 mL over 30 min.
Step 1: Convert time to hours (60 min = 1 hr)
30 min ÷ 60 = 0.5 hr
Step 2: Formula
Volume (mL) ÷ Time (hr) = mL/hr
Step 3: Calculation
100 mL ÷ 0.5 hr
= 200 mL/hr
Half an hour of infusion at this pace would deliver 100 mL, so a full hour would deliver 200 mL.
Answer: 200 mL/hr
Example 3: Another minute conversion
Infuse 50 mL over 20 min.
Step 1: Convert time to hours (60 min = 1 hr)
20 min ÷ 60 = ≈ 0.3333 hr
Step 2: Formula
Volume (mL) ÷ Time (hr) = mL/hr
Step 3: Calculation
50 mL ÷ ≈ 0.3333 hr
= 150 mL/hr
Answer: 150 mL/hr
Common mistakes
Dividing by minutes
- What goes wrong
- 100 mL ÷ 30 = 3.33 mL/hr
- Why it fails
- That's mL per minute, labeled as per hour.
- Correct approach
- 30 min = 0.5 hr; 100 mL ÷ 0.5 hr = 200 mL/hr
Reversing volume and time
- What goes wrong
- 8 hr ÷ 1,000 mL
- Why it fails
- This gives hours per mL, not mL per hour.
- Correct approach
- 1,000 mL ÷ 8 hr = 125 mL/hr
How a rate is rounded or entered depends on the pump and course or facility policy.
Quick self-check
500 mL over 4 hr?
Show the answer
500 mL ÷ 4 hr = 125 mL/hr
For gravity tubing without a pump, see IV drip rate.
Calculate and practice
Related lessons
- IV Drip Rate (gtt/min) — Gravity drops per minute using the tubing's drop factor.
- Infusion Time — Volume ÷ rate, then decimal hours to hours and minutes.
- Nursing Unit Conversions — Move between metric units, pounds and kilograms, and hours and minutes.
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