ATN Blizzard Bag Wk 1/27/2014
CHAPTER 6 Metric and Household Measurements
LEARNING OBJECTIVES
On completion of the materials provided in this chapter, you will be able to perform computations accurately by mastering the following mathematical concepts:
1 Recalling the metric measures of weight, volume, and length
2 Computing equivalents within the metric system by using a proportion
3 Recalling approximate equivalents between metric and household measures
4 Computing equivalents between the metric and household systems of measure by using a proportion
METRIC MEASUREMENTS
The metric system has become the system of choice for dealing with the weights and measures involved in the calculation of drug dosages. This is a result of its accuracy and simplicity because it is based on the decimal system. The use of decimals tends to eliminate errors made when working with fractions. Therefore all answers within the metric system need to be expressed as decimals, not as fractions.
EXAMPLES: 0.5, not ½
0.75, not ¾
0.007, not 7/1000
Certain prefixes identify the multiples of 10 that are being used. The four most commonly used prefixes of the metric system involved with the calculation of drug dosages are the following:
micro= 0.000001 or one millionth
milli= 0.001 or one thousandth
centi = 0.01 or one hundredth
kilo= 1000 or one thousand
These prefixes may be used with any of the base units of weight (gram), volume (liter), or length (meter). The nurse most often uses the following list of metric measures (Box 6-1). Memorize all the entries in the list.
BOX 6-1 COMMON METRIC MEASURES:Metric Measure of Weight:
1,000,000 micrograms (mcg)= 1gm
1000 micrograms (mcg)= 1 mg
1000 milligrams (mg)= 1 gm or “g”
1000 grams (gm or “ g”)= 1 kilogram (kg)
Metric Measure of Volume:
1000 millimeters (ml)= 1 L(Liter)
1 cubic centimeter (cc)= 1 millimeter (ml)
Metric Measure of Length:
1 meter (m)= 1000 mm (millimeter) or 100cm (centimeters)
1 centimeter (cm)= 10mm or 0.01 m
1 millimeter (mm)= 0.1 cm (centimeters) or 0.001 m
Sometimes, to compute drug dosages, the health care professionals must convert a metric measure to an equivalent measure within the system. This may be done easily by using a proportion.
EXAMPLE: 300 mg equals how many grams?
a.On the left side of the proportion, place what you know to be an equivalent between milligrams and grams. From the preceding chart we know that there are 1000 mg in 1 g. Therefore the left side of the proportion would be
1000mg:1g:
b.The right side of the proportion is determined by the problem and by the abbreviations used on the left side of the proportion. Only two different abbreviations may be used in a single proportion. The abbreviations must also be in the same position on the right as they are on the left
1000mg:1g:______mg:______g.
From the problem we know we have 300 mg.
1000mg:1g: 300mg :______g
We need to find the number of grams 300 mg equals, so we use the symbol x to represent the unknown. Therefore the full proportion would be:
1000mg:1g : 300mg : X g .
c.Rewrite the proportion without using the abbreviations.
1000:1: :300 : X
d.Solve for x by multiplying the means and extremes. Write the answer as a decimal, since the metric system is based on decimals.
1000:1::300:X
1000X=300
X= 300 mg
1000 mg
X= 0.3mg
e. Label your answer, as determined by the abbreviation placed next to x in the original proportion.
EXAMPLE 1: 2.5 L equals how many milliliters?
1000 mL : 1 L ::
1000 mL : 1 L ::______mL : ______L
1000 mL : 1 L :: x mL : 2.5 L
1000 : 1 :: x : 2.5
1x= 2500
x= 2500
2.5 L = 2500 mL
EXAMPLE 2: 180 mcg equals how many grams?
1,000,000 mcg : 1 g ::
1,000,000 mcg : 1 g ::______mcg : ______g
1,000,000 mcg : 1 g ::180 mcg : x g
1,000,000 : 1 ::180 : x
1,000,000x = 180
180 mcg = 0.00018 g
EXAMPLE 3: 15 mm equals how many centimeters?
1 cm : 10 mm
1 cm : 10 mm ::______cm : ______mm
1 cm : 10 mm ::x cm : 15 mm
1 : 10 ::x : 15
10x = 1 × 15
10x = 15
15 mm = 1.5 cm
HOUSEHOLD MEASUREMENTS
Household measures are not accurate enough for the nurse to use in the calculation of drug dosages in the hospital. However, their metric equivalents are used in keeping a written record of a patient's “I” and “O,” or intake and output. Always use your institution's conversions when documenting intake. For example, one cup of coffee at one institution may be 250 mL, and at another institution it may be 300 mL.
Memorize the following list of approximate equivalents between metric and household measurements (Box 6-2).
BOX 6-2 METRIC HOUSEHOLD EQUIVALENTS
Metric Measure / House hold Measure5ml / 1 teaspoon (tsp)
15ml / 1 tablespoon (Tbs)
30ml / 1 once (oz)
240ml / 1 cup
1 kg (1000g) / 2.2 pounds (Lbs)
2.5 cm / 2 inch
1 foot (ft) / 12 inches
Conversion of measures between the metric and household systems of measure may also be done by using a proportion, as has been illustrated.
EXAMPLE 1: 1½ cups equals how many milliliters?
a.1 cup : 240 mL ::
b.1 cup : 240 mL ::______cups : ______mL
1 cup : 240 mL ::1½ cups : x mL
c.1 : 240 ::1½ : x
X= 240/1 x 3/2
d. X= 720/2=360mL
e.1½ cups = 360 mL
EXAMPLE 2: 35 kg equals how many pounds?
a.1 kg : 2.2 lb ::
b.1 kg : 2.2 lb ::______kg : ______lb
1 kg : 2.2 lb ::35 kg : x lb
c.1 : 2.2 ::35 : x
d.1x=2.2 × 35
x= 77
e.35 kg = 77 lb
EXAMPLE 3: 18 inches equals how many centimeters?
a.2.5 cm : 1 inch ::
b.2.5 cm : 1 inch ::______cm : ______inch
2.5 cm : 1 inch ::x cm : 18 inches
c.2.5 : 1 ::x : 18
d.x= 2.5 × 18
x= 45 cm
e.18 inches = 45 cm
Name:______Date:______
DIRECTIONS: Change to equivalents within the metric system. Solve the problems by using a proportion. Show your work.PRINT THE WORK SHEET THEN COMPLETE THE CALCULATIONS (60PT) 1PT FOR CORRECT ANSWER AND 1PT FOR SHOWING WORK FOR EACH PROBLEM.
- 230 mcg = ______g
- 5 mg =______mcg
- 2.5 g = ______mcg
- 4000 mcg = ______mg
- 0.33 g = ______mg
- 6 kg = ______g
- 725 mL =______L
8. 2000 mcg = ______g
9. 3 cm = ______mm
10. 620 g = ______kg
11. 0.036 mg = ______mcg
12. 460 mL =______L
13. 0.66 mg = ______mcg
14. 0.5 g = ______mcg
15. 18 inches = ______cm
16. 350,000 mcg = ______g
17. 25 mg =______g
18. 1.46 L = ______mL
19. 2.5 kg = ______g
20. 12 mg = ______mcg
21. 3.4 kg = ______g
22. 920 mcg =______g
23. 25 mm = ______cm
24. 300 mcg = ______mg
25. 0.16 L = ______mL
26. 0.01 g = ______mg
27. 500 mcg =______mg
28. 360 mg = ______g
29. 1.7 L = ______mL
30. 0.45 g = ______mg
Name:______Date:______
DIRECTIONS: Change the following measurements into the approximate equivalents within the metric or household system, as indicated. Solve the problems by using a proportion. Show your work.PRINT AND COMPLETE .20PTS. 1PT FOR CORRECT ANSWER 1 PT FOR SHOWING WORK.
1. 3 inches = ______cm
2. 2¼ cups = ______mL
3. 2 tsp = ______mL
4. 3 Tbsp = ______mL
5. 1½ cups = ______mL
6. 8 kg = ______lb
7. 3825 g = ______lb
8. 7 inches = ______cm
9. 3 lb = ______kg
10. 12 kg = ______lb
11. 1400 g = ______lb
12. 2½ feet = ______inches
13. 150 lb = ______kg