Page 20 - Civil Engineering Formulas

CHAPTER 1
CONVERSION FACTORS

FOR CIVIL ENGINEERING

PRACTICE

Civil engineers throughout the world accept both the United States Customary
System (USCS) and the System International (SI) units of measure for both
applied and theoretical calculations. However, the SI units are much more
widely used than those of the USCS. Hence, both the USCS and the SI units are
presented for essentially every formula in this book. Thus, the user of the book
can apply the formulas with confidence anywhere in the world.
To permit even wider use of this text, this chapter contains the conversion
factors needed to switch from one system to the other. For engineers unfamiliar
with either system of units, the author suggests the following steps for becom-
ing acquainted with the unknown system:
1. Prepare a list of measurements commonly used in your daily work.
2. Insert, opposite each known unit, the unit from the other system. Table 1.1
shows such a list of USCS units with corresponding SI units and symbols
prepared by a civil engineer who normally uses the USCS. The SI units
shown in Table 1.1 were obtained from Table 1.3 by the engineer.
3. Find, from a table of conversion factors, such as Table 1.3, the value used to
convert from USCS to SI units. Insert each appropriate value in Table 1.2 from
Table 1.3.
4. Apply the conversion values wherever necessary for the formulas in this
book.
5. Recognize—here and now—that the most difficult aspect of becoming
familiar with a new system of measurement is becoming comfortable with
the names and magnitudes of the units. Numerical conversion is simple, once
you have set up your own conversion table.
Be careful, when using formulas containing a numerical constant, to convert
the constant to that for the system you are using. You can, however, use the for-
mula for the USCS units (when the formula is given in those units) and then
convert the final result to the SI equivalent using Table 1.3. For the few formu-
las given in SI units, the reverse procedure should be used.

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