How to Calculate IV Flow Rate in mL/hr

An IV pump is set in milliliters per hour (mL/hr). To find the rate, divide the volume to infuse by the time it should take, in hours.

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.

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The steps

Read the volume and the time. Change liters to milliliters (1 L = 1,000 mL).
Put the time in hours. If it is in minutes, divide by 60 (30 min = 0.5 hr).
Divide: mL/hr = volume ÷ hours.
Round the way your pump is set: usually to a whole mL/hr, or to a tenth on pumps that take it.
Check: rate × hours should give back about the volume.

A worked example

Infuse 1,000 mL of normal saline over 6 hours. What rate do you set on the pump?

Volume 1,000 mL, time 6 hours.
Divide: 1,000 ÷ 6 = 166.666… mL/hr.
Round to a whole number: 167 mL/hr (166.7 on a pump that takes tenths).
Check: 167 × 6 = 1,002 mL, about the 1,000 mL ordered.

Set the pump to 167 mL/hr.

Why it works

A rate is an amount for each unit of time, like miles per hour. If 1,000 mL has to go in over 6 hours, each hour gets an equal share: one sixth of 1,000 mL. Dividing the volume by the hours is sharing it out evenly.

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 6 hoursOpens 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 minutes. 100 mL over 30 minutes is 200 mL/hr, not 3.3.
Dividing the wrong way. It is volume ÷ time. 6 ÷ 1,000 is not a rate you can set.
Rounding too early. Divide first, then round once at the end.
Mixing up mL/hr and gtt/min. Pumps use mL/hr; a gravity drip is counted in drops per minute.

Questions people ask

What is the rate for 100 mL over 30 minutes?

30 minutes is 0.5 hour, so 100 ÷ 0.5 = 200 mL/hr.

How long will 1,000 mL take at 125 mL/hr?

Time = volume ÷ rate = 1,000 ÷ 125 = 8 hours. Started at 0700, it finishes at 1500.

How do I set a rate for a dose like 2 mg/hr?

Find the concentration first: 100 mg in 100 mL is 1 mg/mL, so 2 mg/hr needs 2 mL/hr.

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