Objectives

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

1/16″.

• Add and subtract fractions and whole

numbers.

• Compute pipe offsets using the Pythagor-

ean theorem and trigonometric functions.

• Apply the formulas for finding area and

volume.

• Explain and apply SI metric measure in find-

ing length, area, volume, and temperature.

• Convert customary measure to metric

measure.

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

Measurement

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

examples.

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

1/16″

is easy if the

1/4″

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

Plumbers

4

87

Pythagorean theorem

Trigonometric

functions

Laying length

Plumber’s rule