This chapter reviews the basic mathematics
likely to be needed by the plumber.
After studying this chapter, you will be able to:
Read a rule accurately to nearest
Add and subtract fractions and whole
Compute pipe offsets using the Pythagor-
ean theorem and trigonometric functions.
Apply the formulas for finding area and
Explain and apply SI metric measure in find-
ing length, area, volume, and temperature.
Convert customary measure to metric
Plumbers need to make accurate measure-
ments and calculations. They need to add and
subtract dimensions, compute pipe offsets, and
determine the volume of tanks. This chapter
will provide the basic information needed to
master these skills. In addition, metric meas-
urement is introduced.
Technical Terms
The basic measuring tools used by the
plumber are the folding rule and the steel tape.
Whichever is used, the scale printed on the tool
is the same. Figure 4-1 illustrates how the
basic scale is divided into parts of an inch.
Reading Fractions of
an Inch
Reading a rule accurately and quickly
requires careful attention to the markings on
the scale and some practice. The lines marking
the scale vary in length. The longest lines are
the inch divisions. The shortest lines indicate
sixteenths of an inch. Figure 4-2 gives several
To prevent costly errors, recheck each
measurement before cutting materials. The
reduced waste in both time and materials
makes this procedure worthwhile.
Reading a scale accurately to the nearest
is easy if the
divisions are used as a
starting point and the smaller parts of an inch
are added to or subtracted from the larger divi-
sions to get the correct reading. See Figure 4-3.
This method is much faster and more accurate
than attempting to count the number of spaces.
Mathematics for
Pythagorean theorem
Laying length
Plumber’s rule
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