8 The Metric System

Student Learning Outcomes Name the units in the metric system Convert metric units to standard units Complete metric-to-metric conversions Use ratio and proportion to make dental stone measurements Identify how the metric system is used in the health care field After completing the tasks in this unit, you will be able to: Name the units in the metric system Convert metric units to standard units Complete metric-to-metric conversions Use ratio and proportion to make dental stone measurements Identify how the metric system is used in the health care field

Metric System in Health Care 8-5 Metric measurements are used in health care for: Weight calculations Dosage calculations Food intake (in grams) measurements Metric measurements are used for many types of measurements in the health care professions. Some uses include the following: • weight calculations • dosage calculations • food intake (in grams) measurements • height and length measurements • liquid and medication measurements

Metric System in Health Care 8-5 Metric measurements are used in health care for: Height and length measurements Liquid and medication measurements Metric measurements are used for many types of measurements in the health care professions. Some uses include the following: • weight calculations • dosage calculations • food intake (in grams) measurements • height and length measurements • liquid and medication measurements

Base Units Metric base units measure Volume, weight, length 8-1 MEASUREMENT EXAMPLES Liter (l or L) Volume Liquids, blood, urine Gram (g or G) Weight An item’s weight An amount of medicine Meter (m) Length Height, length Metric units come in base units. These units measure different types of materials. Measurement types are volume, weight, and length. Here we see examples of the various measurements. A liter is for volume and measures liquids. A gram is for weight and measures weight or amount. A meter is for length and measures height or length.

Multiples of 10 Metric system 8-1 Metric system Based on multiples of 10 (easy conversion!) The metric system uses units based on multiples of ten. For this reason, metric numbers are written in whole numbers or decimal numbers, but never as fractions. You can solve metric conversion problems by moving the decimal either to the left or to the right. This table shows the different units, their value, their symbol, and their mnemonic device for remembering. Using a mnemonic device helps keep the metric units in the correct sequence or order. Try something silly like Mom’s advice to: “kiss hairy dogs but drink chocolate milk, mom.” Knowing a device like this will help you remember the order of the units on an exam. Note that the mo (in “mom”) are placeholders. This helps you remember to count the spaces in the mnemonic device. So, remember Mom’s advice: Kiss Hairy Dogs But Drink Chocolate Milk, moM You can use the first letters of the metric units to recall their order by writing them on a piece of scratch paper or an answer sheet on examination days.

Multiples of 10 Mnemonic for remembering units 8-1 Mnemonic for remembering units Kiss Hairy Dogs But Drink Chocolate Milk, moM The metric system uses units based on multiples of ten. For this reason, metric numbers are written in whole numbers or decimal numbers, but never as fractions. You can solve metric conversion problems by moving the decimal either to the left or to the right. This table shows the different units, their values, their symbols, and the mnemonic device for remembering their order. Using a mnemonic device helps you keep the metric units in the correct sequence or order. Try something silly like: “kiss hairy dogs but drink chocolate milk, mom.” Knowing a device like this will help you remember the order of the units for an exam. Note that the letters mo (in “mom”) are place holders. They help you remember to count three spaces from "milli-" to "micro-" . So, remember: Kiss Hairy Dogs But Drink Chocolate Milk, moM You can use the first letters of the metric units to recall their order by writing them on a piece of scratch paper or an answer sheet on examination days.

Using Metric Symbols Forming metric units 8-1 Forming metric units Prefix + base element (root) = metric unit The metric system combines prefixes (word parts that come first) with root words (the base unit). Together, the prefix and root indicate the type of measurement, as in volume, weight, or length. For example, in the word “kilogram,” kilo- is the prefix and means thousand and gram is the root and means weight. Centi- is the prefix and means hundredth and meter is the root and indicates length. The prefixes are the key to deciphering what number of units you have. Every metric prefix may be combined with every root. The application of these terms depends on the measurement being conveyed. Thus, liquids are measured in liters, and dry medications are measured in grams because this type of medication is measured by weight.

Using Metric Symbols 8-1 Every metric prefix may be combined with every root. Example: kilo (thousand) + gram (weight) = kilogram (kg Example: centi (hundredth) + meter (length) = centimeter (cm) The metric system combines prefixes (word parts that come first) with root words (the base unit). Together, the prefix and root indicate the type of measurement, as in volume, weight, or length. For example, in the word “kilogram,” kilo- is the prefix and means thousand and gram is the root and means weight. Centi- is the prefix and means hundredth and meter is the root and indicates length. The prefixes are the key to deciphering what number of units you have. Every metric prefix may be combined with every root. The application of these terms depends on the measurement being conveyed. Thus, liquids are measured in liters, and dry medications are measured in grams because this type of medication is measured by weight.

Changing Unit Measures 8-3 What if Rx doesn’t match supply? Change the units! Count difference in number of spaces (go right or go left) In health care, sometimes a doctor’s order comes in micrograms, but your supply on hand comes in milligrams. You need to convert from micrograms to milligrams to ensure accurate dosing. To change units within the metric system, count the spaces from the number you are starting with to the unit you are converting to. You’ll go either right or left. Note that the m and o in “mom” are place holders and hold no value. They are included only to help you remember to count three spaces from milli- to micro-. For example, from gram to milligram, are three spaces. Note that the direction from gram to milligram is to the right. Move the decimal three places to the right. Thus, 45.5 grams = 45500 milligrams. Note that most health care conversions are done between kilogram and gram, gram and milligram, milligram and microgram, meter and centimeter, and liter and milliliter. With practice, you will discover that converting between units begins to feel natural. Practice making the conversion by moving the decimal from one unit to another. Use a pencil to draw the “U” as you count the spaces. Start at the existing decimal and move to the right (or left) of each metric unit. Remember that the “b” in the mnemonic stands for the base units of meters, liters, or grams.

Changing Unit Measures 8-3 Problem: 45.5 grams = ___ milligrams 4 5 . 5 0 0 grams 45500. milligrams So, 45.5 grams = 45500 milligrams In health care, sometimes a doctor’s order comes in micrograms, but your supply on hand comes in milligrams. You need to convert from micrograms to milligrams to ensure accurate dosing. To change units within the metric system, count the spaces from the number you are starting with to the unit you are converting to. You’ll go either right or left. Note that the m and o in “mom” are place holders and hold no value. They are included only to help you remember to count three spaces from milli- to micro-. For example, from gram to milligram, are three spaces. Note that the direction from gram to milligram is to the right. Move the decimal three places to the right. Thus, 45.5 grams = 45500 milligrams. Note that most health care conversions are done between kilogram and gram, gram and milligram, milligram and microgram, meter and centimeter, and liter and milliliter. With practice, you will discover that converting between units begins to feel natural. Practice making the conversion by moving the decimal from one unit to another. Use a pencil to draw the “U” as you count the spaces. Start at the existing decimal and move to the right (or left) of each metric unit. Remember that the “b” in the mnemonic stands for the base units of meters, liters, or grams.

So, 50 milliliters = 0.05 liters Another Example 8-3 Problem: 50 milliliters = ___ liters 50. 0 0 5 0 . 0.050 = 0.05 So, 50 milliliters = 0.05 liters Let’s look at another example. Problem: 50 milliliters = ___ liters We write 50, adding the implied decimal point (50.). Now we count the spaces between liters and milliliters = 3. So, we move the decimal point 3 spaces to the left from milliliters to the base, liters (we have to add some zeros for place holders). So, 50 milliliters = 0.05 liters.

Practical Example Formula: ratio of dental stone to water 8-4 Formula: ratio of dental stone to water Problem: For 35 mL water, how much stone to use? Sometimes dental assistants need to mix dental stone material for dental molds. The amount of stone and water varies according to the size of the mold needed. A dental assistant learns the importance of mixing a uniform and consistent material for the mold. This task uses the metric system: Dental stone is measured by weight in grams and room temperature water is measured by volume in milliliters. Knowledge of the metric system coupled with the use of ratio and proportion help maintain the correct ratio of dental stone to water. The typical ratio of dental stone to water is: (263 GRAMS OF DENTAL STONE POWDER)/(80 MILLILITERS OF ROOM TEMPERATURE WATER) Dental assistants use this ratio as the standard to solve variances in either stone or water to create the proper amount of material for the mold. On occasion, they may be asked to use other ratios of dental stone to water, depending on the type of material or the mold being created. Here is a practical example from real life. We’ll use proportion to solve this problem. If the dentist requests a smaller mold using 35 mL of water, how much stone should be used? The problem set up is: 263 g over 80 mL = how many g over 35 mL Multiply 263 by 35 to get 9205. Divide 9205 by 80 (the remaining number) to get 115.0625. Round this to the nearest whole number to get 115 grams for 35 mL of water.

Converting Metric Units to Standard Units 8-2 1 teaspoon is ____ mL 1 kg = ____ lbs Answers: 5 2.2 lbs