How to Use Conversion in Nursing Math

Knowing how to convert medication doses safeguards your patients.

Knowing how to convert medication doses safeguards your patients.

Nurses need to know how to convert measurements to administer medications and fluids. A physician orders medication with the dose written in milligrams (mg), for example. To administer the medication you must draw it up in a syringe. But syringes aren't marked in milligrams. You must convert the milligram dose to an amount that you can measure in a syringe, measuring cup or other device, such as a milliliter or cubic centimeter.

Read the physician's order to see if you need to do a medication dose conversion. A typical order might say to give a dose such as 5 mg of a medication, or to give 1.5 teaspoons of a liquid. To determine the first, you need to know how many milligrams of the medication are in 1 milliliter or cc. To determine the second, you need to know how many milliliters are in a teaspoon.

Figure out the type of dose conversion you need by checking the syringe or other administering device, such as a measuring cup. Most medications will be given in syringes or medication cups marked in milliliters or cubic centimeters. Milliliters and ccs are two different names for the same amount; 1 cc equals 1 ml. A typical syringe might have both designations or one or the other.

Determine how to convert your dose. You may need to multiply to get the dose you need, or you might need to divide. If, for example, the 5-mg medication dose ordered is for a medication that comes mixed at a concentration of 2.5 mg per ml, you will need to multiply, because you need more medication than is in 1 ml. If the medication comes mixed with 10 mg per ml, you will need to divide. In many conversions, you need to do both multiplication and division.

Do the math, using a calculator if necessary. A typical conversion will go like this. The order states to give 6 mg of medication. The bottle you have contains 2 mg per ml. You need to determine how many milligrams are in each milliliter, because your syringes are marked in milliliters. You can do this in one of two ways. Divide 2 into 6, which equals 3. You need 3 x 1 ml, or 3 ml. Alternatively, divide 1 ml by 2 mg to determine how many milligrams of medication are in 1 ml. You find that 1 milliliter contains 0.5 milligrams of medication. Since you need to give 6 mg of medication, multiply 6 x 0.5. The answer is 3. You will give 3 ml of medication.

Double-check your math. Even if the pharmacy sends up a medication with the dose already computed, check it yourself. If a dose seems too large -- for example, if you need several syringes to give a single medication dose -- check the order again. Rarely should you need to use more than one syringe to dispense a medication, or give more than two pills at one time, the American Society of Hospital Pharmacists warns.

Items you will need

  • Calculator

Tips

  • Some medications conversions are simple enough to do in your head. But it never hurts to double-check your work with a calculator.
  • Always ask yourself, "Does this conversion make sense?" If the answer seems wrong, ask someone else to check your calculations.

Warning

  • Pharmacies, and nurses, can make potentially deadly mistakes if they don't double-check their work. Don't hesitate to question an order that doesn't seem right.
 

About the Author

A registered nurse with more than 25 years of experience in oncology, labor/delivery, neonatal intensive care, infertility and ophthalmology, Sharon Perkins has also coauthored and edited numerous health books for the Wiley "Dummies" series. Perkins also has extensive experience working in home health with medically fragile pediatric patients.

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