1. Metric/International (SI) System
Chapter 4
Metric/International (SI) System
PNU 145, September.
Cheryl Proffitt, RN,MSN

2. Metric System Système International (SI)
Developed in France in 1875
Name stems from basic unit of measure
Takes its name from Meter, length equivalent to yards

3. Metric/SI System Major strength of SI system is that ___
All units of measure differ from each other in powers of ten
Conversions between units accomplished by simply moving the decimal point.
NOTE: be careful when moving the decimal point it can alter the dosage if done incorrectly.

4. Examples of larger units/smaller
Units of measure comparison in terms of smaller and larger units
Pounds is larger than ounces.etc.

5. Basic Units of measure
Length
Meter
Volume
Liter
Weight
Gram

6. Terms with Prefixes
Whether larger or smaller than basic units, all other units have name of basic unit incorporated in them
E.g., kilogram, centimeter, milligram, microgram
Same prefixes can be used with all three measures
For example- kilometer, kilogram and kiloliter
Prefixes can also units that are larger or smaller.
Kilo is often used in clinical areas especially for weights

7. Terms with Prefixes 1 kilometer =1000 meters 1 kilogram =1000 grams
1 kiloliter = 1000 Liters
Some other units used in clinical areas are
Milli – milligram- weight
Micro-microgram- weight
Centi- centimeter- Length
Putting it all together the four basic units in clinical areas –Kilo, centi, micro,milli.

8. Abbreviations
How to abbreviate-the basic units are abbreviated to their first initials and printed in small lower case letters. Exception is Liter with upper case L
Gram (g)
Milligram (mg)
Microgram (mcg)
Liter (L)
Milliliter (mL)
Kilogram (kg)
Kilometer (km)

9. Why is Liter with L
"L" is the symbol for liter, not abbreviation  the use of capital has suggested from National Institute of Standards and Technology because "l" looks like numb 1, so L is safer and is recommended.

10. Notation Rules Units of measure are expressed in
Quantity - written in Arabic numbers
1, 2, 3, 4, etc.
E.g., 0.5 (mL) 1(mL),
Numerals representing quantity placed before abbreviations
E.g., 0.5 mL, 1mL ( not mL 0.5)

11. Notation Rules Full space used between number and abbreviation
E.g., 0.5mL ( not 0.5mL)
Fractional parts of unit are written in decimal fractions
E.g., 0.5 mL ( not 1/2mL)

12. Notation Rules
Zero placed in front of decimal point when not preceded by whole number
Emphasizes decimal point
E.g. 0.5mL (not .5mL)
Excess zeros following decimal fraction eliminated
E.g., 0.5mL ( not 0.50mL)

13. Common Weight Units Used in Health Care
From Greater to Lesser values
kg = kilogram
g = gram
mg = Milligram
mcg = Microgram

14. Common Volume Units Used in Health Care
Units of volume frequently used are . From greater to lesser values
L = Liter &
mL = milliliter

15. Conversion continues.
Each of the clinical metric measures differs from the next by For example from greater to larger.
1kg = g
1g = 1000 mg
1mg = 1000 mcg
1L = mL.
Recap: Values from greater to lesser for weights are as follows kg, g, mg, mcg.
Differ by 1000

16. Metric Conversions
Metric system is decimal system, so conversion between units are accomplished by moving the decimal point
The decimal is moved according to difference in value, for example if difference in value is
10- which has one 0, move decimal one place.
100- which has two 0, move decimal two places
1000- which has three 0, move decimal three places

17. Conversions Which way do you move decimal point
Values from greater to lesser for weights are as follows kg- g- mg- mcg.
When converting to a smaller units of measure , for example g to mg. ( g is larger and mg is smaller unit).We know that the decimal point is moved 3 places to the right

18. Conversions For example: 0.5g to mg
Move decimal point 3 places to the right
0.5= 0.500
Eliminate the 0 at the front
So now we have a larger unit of 500mg
Even though you are converting to a smaller unit, the quantity will be larger.

19. Conversions
If you are converting from a smaller to larger unit of measurement such as mL to L, move decimal point three places to the left.
For example 200mL to L
200 ml to L= move 3 places to Left
.200 .=
Eliminate 2 zeros at end, and add 0 before the point= 0.2L

20. Conversions tips Large to small –3places to right
Small to large – 3 places to left

21. References
Curran, A.Witt, M. (2014) Math for Meds, dosage and solutions. ( 11th ed) . Cengage learning, Stamford, CT.