Tablet dosage calculation

The most important piece of information you need to figure out how many tablets will be given to a patient is the dosage strength. The dosage strength is on the medication label.

I created a generic medication label below to help see where to get the dosage strength.

As a nursing student, you may know this already. Great! My job is to help you understand the math behind dosage calculation

There are 4 basic information on a medication label: The trade name, the generic name, the dosage strength, and the total number of tablets

Medication-label

Trade name:
  • Written on top of the generic name
  • Usually bigger in font size than the generic name
  • Written sometimes in capital letters

The generic name or official name is usually written in lower case letter

Dosage:
  • The unit for the dosage strength is mostly expressed in mg (milligrams) and sometimes mcg (micrograms). That is how you will recognize it!

  • The dosage strength is the strength of 1 tablet.

Example #1:

Say the dosage strength is 100 mg and there are 200 tablets in the bottle. If the doctor orders 300 mg, how many tablets will you give?

100 mg + 100 mg + 100 mg = 300 mg

As you can see, you need 3 tablets of 100 mg to reach the dosage of 300 mg ordered by the doctor. Therefore, you will give 3 tablets

Example #2:

Say the dosage strength is 100 mg and there are 100 tablets in the bottle. If the doctor orders 50 mg, how many tablets will you give?

50 mg =
100 mg / 2


Therefore, you will give half a tablet

Observation:

tablets given in example #1 =
300 mg / 100 mg
= 3 tablets


tablets given in example #2 =
50 mg / 100 mg
= 0.5 or half a tablet


Generally speaking,

Number of tablets to give =
Medication strength ordered by the doctor / Dosage strength of 1 tablet


Example #3:

Say the dosage strength is 200 mg and there are 100 tablets in the bottle. If the doctor orders 0.4 g, how many tablets will you give?

Before you use the formula above, all units should be the same. Thus, convert 200 mg to g.

200 mg = 0.2 g

number of tablets to give =
0.4 g / 0.2 g


number of tablets to give =
4 g / 2 g
= 2 tablets


Tablet dosage calculation quiz:











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