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Figuring IV flow rate, infusion time, and total volume

Figuring IV flow rate, infusion time, and total volume

Whenever you’re administering intravenous (IV) infusions, you need to know the flow rate, infusion time, and total volume. Fortunately, calculating any one of these three variables is easy to do when you know the other two variables. Use the following equations:

  • flow rate (mL/hr) = total volume (mL) ÷ infusion time (hr)

  • infusion time (hr) = total volume (mL) ÷ flow rate (mL/hr)

  • total volume (mL) = flow rate (mL/hr) × infusion time (hr)

For example, if you must administer 1 L (1,000 mL) of fluid over 4 hours, use the first formula to calculate the flow rate, like so:
flow rate (mL/hr) = total volume (mL) ÷ infusion time (hr)
flow rate (mL/hr) = 1,000 ÷ 4
flow rate (mL/hr) = 250
The flow rate is 250 mL/hr.

Common conversion factors in medical dosage calculations

As a healthcare professional, you have to convert patient weights, fluid volumes, medication weights, and more. Conversion math isn’t hard to do as long as you know the basic conversion factors. Here are the most useful ones:

  • Converting lb to kg and kg to lb

    lb = kg × 2.2

    kg = lb ÷ 2.2

  • Converting mL to L and L to mL

    mL = L × 1,000

    L = mL ÷ 1,000

  • Converting mg to g, g to mg, mg to mcg, and mcg to mg

    mg = g × 1,000

    g = mg ÷ 1,000

    mcg = mg × 1,000

    mg = mcg ÷ 1,000


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