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Conversion between Different Units

Objectives Convert between the different systems of measurement.

Table 2-3 contains a table with conversion factors. It is not an exhaustive table, but may be used for the exercises in this book.

The table lists conversion factors that may be used to solve engineering problems. Some values are approximate

Dimension	Conversion Factor
length	0.3048 m = 1 ft
area	1 m2 = 10.764 ft2 = 1550 in2
Mass	1 kg = 2.2046 lbm
Volume	1 m3 = 264.2 gal = 35.32 ft3
velocity	1 m/s = 3.2802 ft/s = 2.237 mi/h
Acceleration	1 m/s2 = 3.2808 ft/s2
Force	1 N = 0.22481 lbf
Pressure	1 kPa = 0.14504 lbf/in2
Temperature

Except for the definition of mass, the BGS and the EE system have identical units. Conversion between these two units of measurement is straightforward. Because 1 Lbf accelerates 1 Lbm at 32.174 ft/sec², 32.174 Lbm would be accelerated at 1 ft/sec². Therefore,

Expression (2.4) may be used to convert between units of Lbm and slug.

In general, a conversion factor exists between equivalent units. For example, 1 ft = 0.3048 m. When using conversion factors, keep track of the units. In your result, all but the desired unit should drop out from the expression.

EXAMPLE

A structural component has a length of 2 ft 3 inches. What is the corresponding length in centimeters? SOLUTION The conversion between feet and meters is given in Table 2-3 (in particular, 1 ft = 0.3048 m). First, we use the fact that there are 12 inches per foot. Thus, 2 ft 3 inches is equivalent to which allows us to convert to meters. Thus, Notice how all but the units of centimeter drop out in the expression.

 

Professional Success

As we have seen, there are three commonly used systems of measurement in engineering. Although the metric system is gaining in popularity, BGS and EE system are still used. Be very careful when performing calculations with values associated with different systems of measurement.