NCLEX: Basic calculations For Nurses

Calculations
Math calculation is an integral part of safe nursing care. This section is a review of the conversion tables and sample problems.

The Apothecary System of Measurement
Equivalents/Conversion Factors
1 minim = 1 drop
1 fluid dram = 60 minims
1 fluid ounce = 8 fluid drams
1 dram = 60 grains
30 ml = 2 tbs (tablespoons)
15 ml = 1 tbs
5 ml = 1 tsp (teaspoon)

The Household System of Measurement
Equivalents/Conversion Factors
1 teaspoon = 60 drops
2 tablespoons = 1 ounce
1 cup = 8 ounces
2 cups = 1 pint
2 pints = 1 quart
4 quarts = 1 gallon
1 pound = 16 ounces
1 teaspoon = 15–16 minims = 5 mL (milliliter)

2.2 pounds = 1 kilogram = 1000 gm (gram )

Metric Measurements
Equivalents/Conversion Factors
1 gr (grain) = 60–65 mg (milligram)
1 mg = 1000 mcg (microgram)
1 gm = 1000 mg = 15 gr
1 kg = 2.2 lbs

Test Your Math Skills

1. The doctor has ordered a nitroglycerin infusion to infuse at 15 mcg/minute. Available is 50 mg of nitroglycerin in 250 mL. A microdrop set is utilized to administer this medication. How many mL per hour will the nurse infuse? (In a microdrop set, the number of gtts per minute equals mL per hour.)

2. The doctor has ordered one unit of blood (500 mL) to be given over four hours. After verifying the order, calculate the rate in gtts/minute. (A 20 drop per mL blood set is available.)

3. The doctor has ordered 15 mg of Demerol (meperidine) for pain. Available is Demerol 25 mg per mL. How many mL will you administer?

4. The doctor has ordered 250 mg of Aldomet (methyldopa) for control of the client’s primary hypertension. The pharmacy sent the medication labeled 1 tablet contains 125 mg. How many tablets will you administer?

5. The doctor has ordered 35 mg of Demerol (Meperidine) IM stat for pain. Available is 1 mL containing 50 mg. How many ml will you administer?

6. The doctor has ordered doxycycline (Vibramycin) 100 mg orally every 12 hours. The pharmacy sent the medication labeled 50 mg/5 mL. How many mL will you administer?

7. The doctor has ordered digoxin (Lanoxin) 0.25 mg orally qd (every day). The tablets are labeled 0.50 mg per tablet. How many tablets will you give?

8. The doctor has ordered a medication labeled gr 1/300 for atrial fibrillation. The cart contains a unidose container labeled 0.1 mg per tablet. How many tablets will you administer ?

9. The doctor has ordered acetaminophen (Tylenol) gr 10 orally every four hours for headache. Available is 325 mg in one tablet. How many tablets will you administer?

10. The doctor has ordered glycopyrrolate (Robinul) 0.2 mg intramuscular. Available is 0.6 mg in one mL. How many mL will you administer?

11. The doctor has ordered phenytoin (Dilantin) 5 mg/kg of body weight to be given to the client with seizure disorder. Available is Dilantin 50 mg in 1 mL. How many mL will you administer to the client who weighs 110 pounds?

12. The doctor has ordered heparin 7500 units subcutaneously. Available is heparin 5000 units per mL. How many mL will you administer?

Answers

1. 4.5 or 5 mL/hr

2. 42 gtt/1 minute

3. 15 = .6 mL

4. 250mg = 2 tablets

5. .7 mL

6. 10 mL

7. .5 tablet

8. 2 tablets

9. 2 tablets

10. .3 mL

11. 5 mL

12. 1.5 mL