Dosage Practice

IV Flow Rate Calculation: mL per Hour on a Pump

A pump is set in milliliters per hour, so divide the total volume by the time in hours. If the time is in minutes, divide the volume by the minutes and multiply by 60, or convert the minutes to a fraction of an hour first.

The Formula

mL/hr = total mL ÷ hours mL/hr = (total mL ÷ minutes) × 60

Pumps take whole numbers, so round to the nearest whole mL/hr unless your pump accepts tenths.

How to work it out

  1. 1 Find the total volume and the total time in the order.
  2. 2 Get the time into hours. 30 minutes is 0.5 hr; 6 hr 40 min is 6 + 40 ÷ 60 = 6.67 hr. Never write 6.40.
  3. 3 Divide volume by hours.
  4. 4 Round to the nearest whole number, because most pumps only accept whole mL/hr.

Worked Examples

Example 1

Order: 1,000 mL of normal saline IV over 8 hours. Pump rate in mL/hr?

  1. 1,000 mL ÷ 8 hr = 125 mL/hr.

Answer: 125 mL/hr

Example 2

Order: cefazolin in 100 mL to infuse over 30 minutes. Pump rate in mL/hr?

  1. 30 minutes is 0.5 hour.
  2. 100 mL ÷ 0.5 hr = 200 mL/hr.
  3. Or: 100 ÷ 30 × 60 = 200.

Answer: 200 mL/hr

Try five free problems

One exact answer, rounded as asked, no partial credit. No sign-up needed.

Problem 1 of 5No sign-up needed

Order: 1,000 mL of lactated Ringer's IV over 5 hr 15 min. At what rate will you set the pump, in mL/hr?

round to the nearest whole number

mL/hr

Common Mistakes

  • Writing 6 hr 40 min as 6.4 hours

    40 minutes is 40 ÷ 60 = 0.67 of an hour, so the time is 6.67 hours. Treating minutes as decimals makes the rate too high.

  • Stopping at mL per minute

    100 mL over 30 minutes is 3.3 mL per minute, but the pump is set per hour: multiply by 60 to get 200 mL/hr.

  • Multiplying instead of dividing

    Rate is volume divided by time. A rate larger than the total volume for a multi-hour infusion is a sign of this.

Questions Students Ask

What if the pump accepts decimals?

Some pumps, especially in pediatrics, accept tenths. The question will say so. If it does not, round to the nearest whole number.

How is this different from drops per minute?

mL/hr is for pumps. Drops per minute is for gravity tubing and needs the tubing's drop factor. That is the next lesson.

Keep practicing in lesson 9: IV Flow Rate on a Pump (mL/hr)

Fresh numbers every time. Ten correct answers finish the lesson. The practice round and the first five problems of lesson 1 are free.

Open lesson 9