Fundamentals session 3: Intro to dosage calculations

Introduction to dosage calculations

The takeaway here is attention to detail, double check your math and find a comfortable system to do your dosage calculations.

Medications errors happen and nurses or pharmacist need to catch them.


Dose calculations probably do not match what was ordered.


Volume is the amount of fluid

  • concentration is the amount of drug per the volume
  • concentration may vary widely in the volume.


Always use the smallest unit used

  • 60 mg = 1 grain (gr) grain is not too common
  • 30 ml = 1 fl. ounce
  • 1 mg = 1000 mcg
  • 1 Gm = 1000 mg

basic dosage calc

  • Order – what the doc wants
  • available – what we have


Always write 0.5 Gm not .5 Gm


know how to read your labels


there are many ways to do a basic dosage calculation


IV Calculations


Using IV pump – Overall volume to be infused/ the time of volume to be infused

  • volume in ml
  • time in hours
    • divide out for rate


Manual drip (gtt) on the NCLEX

  • drops per minute (gtt/min)
  • drop factor: the amount of drops it takes to make a ml (gtt/ml)
  • (solution times drop factor) over (hours times 60)



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