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Orders read give "gr X" (grains 10) Tylenol q 4-6 prn.  How many milligrams of acetaminophen do you give?

Answer:  You don't give any.  Many facilities consider the use of grains archaic and a source of medical errors.  Depending on the source, 5 grains can equal 300-325 mg.  Now consider many medications are measured and given in hundredths of milligrams: the difference of 25 mg could have disastrous consequences.  The best solution is to have the doctor rewrite the order in milligrams.

For educational purposes this calculator considers 1 grain = 64.8 milligrams however the National Weights & Measures Laboratory considers 1 grain = 64.79891 milligrams.  My nursing text book vacillates between 1 grain = 60-64 milligrams.  If you were to solve this problem using this calculator the answer would be 648 milligrams (roughly 2 plain acetaminophen tablets).


All measurements were referenced from a nursing text book except cups and grains.


    Munday, L. D., & Curren, A. M. (1990). Math for meds: Dosages and solutions. (6th ed.). San Diego, CA: Wallcur Inc.

    Hand, M. S., Thatcher, C. D., Rimillard, R. L., & Roudebush, P. (Eds.). (2000) Small Animal Clinical Nutrition. (4th ed.). Marceline, MO: Walsworth.

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