Many students struggle in their Dosage Calculations nursing school class. While the math can be difficult to learn at first, it does get much easier in time. Here are some tests you can practice:
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All nurses need to be competent in the calculation of medication dosages. You need to know how to calculate required dosages accurately, including doses of tablets, doses of solutions, and intravenous fluid rates and medications.
These drug calculations will require the application of some basic mathematics such as addition, subtraction, multiplication, and division. You will also need to be able to:
Before starting, you may want to review your knowledge on basic mathematic calculations and fractions, percentages, and decimals. There are lots of online resources to help you develop and practice your maths skills.
Calculating Doses
Drugs may be administered via several routes. Drugs that are administered orally are usually in tablet, capsule or liquid form. Drugs can also be administered by injection or intravenous infusion. You will need to be able to calculate dosages for oral and liquid medications.
When using formulas, the most important step is to identify and understand what each part of the formula means. Before applying the formula to calculate medication dosages, review important concepts that will help you identify what information you need to look for, and how to use the formula.
The following tutorials are an introduction to basic drug calculations for nursing. After each tutorial, test your knowledge with the interactive activities.
Medication dosage orders are provided and dispensed in a variety of ways. It is important that you familiarise yourself with the terminology used to measure weight and volume, and how to convert from larger to smaller units - and vice versa.
When applying formulas to calculate dosages, make sure that you are using the same units of measurement; this means that, in some cases, you will need to convert units of measurement. This section will show you how weight and volume are measured.
Units of measurement: Weight
The gram is the basic unit of weight. The most common multiple of a gram is the kilogram, which is 1000 times greater than the gram. The most common subdivision of a gram is the milligram, which represents 1/1000 of a gram- or 0.001 g. The table below shows equivalencies between units of weight:
Units of measurement: Volume
The liter is the basic unit of volume; a subdivision of a liter is the milliliter. The table below shows the equivalence between liter and milliliter:
Converting from larger to smaller units
Because all metric units are multiples or subdivisions of the major units, you can convert units by dividing by the appropriate multiple or multiplying by the appropriate subdivision.
If you need to convert between a larger a smaller unit (for example, from kilogram to gram), you will multiply by 1000, or move the decimal point 3 places to the right.
2 kg will convert to 2000 g
2kg x 1000= 2,000g
Or move the decimal point 3 places to the right: 2kg ► 2000 g
3.4 L x 1000= 3400 mL
Or move the decimal point 3 places to the right: 3.4 L ► 3400 mL
Converting from smaller to larger units
To convert from smaller to larger units, divide by 1000 or move the decimal point three places to the left.
300mg/1000= 0.3 g
OR move decimal point three places to the left 300 mg ►0.3 g
1700 mL/1000 = 1.7 L
OR move the decimal point three places to the left
1700 mL ►1.7 L
When working with time, you will need to be able to convert time into fractions and then decimals. This is needed in order to calculate IVT rates, for example.
First of all, make sure you are familiar with how time is measured and the equivalencies between units of time:
For instance, one hour and fifteen minutes can be expressed as a fraction:
1 ¼
To convert the fraction ¼ into decimals, you will divide the top number by the bottom number in the fraction: ¼= 0.25
Thus, one hour and fifteen minutes can be expressed as 1.25 hr (1+0.25)
If you have to convert minutes into decimals, you will follow a similar procedure:
15 minutes can be expressed as a fraction of an hour: 15/60 mins
If we divide the top number by the bottom number, we obtain 0.25 hr
Remember to always include the unit of time measurement that you are using.
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