# Math Study Guide

Nursing Math Study Guide

The right patient

The right drug

The right dose

The right route

The right time

Tips and Common Errors

- The metric system is used in hospitals, and common mistakes include using the weight

in pounds instead of kilograms, completing conversions incorrectly, or making a

calculation error.

- Complete any conversions first (pounds into kilograms, ounces into milliliters, etc.)

before solving the problem.

Common Conversions

1g = 1000 mg

1L = 1000 ml

1 kg = 2.2 lbs

1 oz = 30 ml

1 teaspoon= 5 ml

1 tablespoon = 15 ml

Mathematical Techniques

Let’s imagine that the dosing for medication A is 30 mg/kg. Our patient weighs 7 kg. How would we find the correct dose? This is where cross multiplication comes in:

30 mg   x   30 mg  x 7 kg = 210 /1 kg = 210 mg of medication

______     =  ______

1kg                7kg

The other option is to multiply as shown in the second example.

Practice Problems

Problem 1:

A 3-year-old male comes into clinic with a temperature of 103F. He weighs 25 lbs and the

provider orders acetaminophen at 15 mg/kg. The concentration of the medication is listed on

the bottle as 160 mg/ 5 mg. How many milliliters of acetaminophen should the nurse

Problem 2:

physician orders cefepime 100 mg/kg/day in two divided doses. Your patient weighs 10.8 kg.

The concentration of the cefepime is 2 g/100 ml. How many milliliters of cefepime will you