computing the area of circles requires the use of
one of two special formulas:
Area = πr2
or
Area = .7854d2
These formulas read: “area equals pi times
the radius squared” and “area equals .7854
times the diameter squared.”
Pi is a mathematical ratio frequently used
when making calculations about circles. For
most practical purposes, pi can be assumed to
be equal to 3.14. Figure 4-21 illustrates the use
of the area formulas for circles.
Volume of a rectangular tank is found by
multiplying length, width, and height as
shown in Figure 4-22.
Finding the volume of cylindrical tanks
requires the use of the formula:
Volume = πr2h
This is read: “volume equals pi times the
radius squared times the height.” Figure 4-23
illustrates the use of this formula.
After calculating volume in some conven-
ient units of cubic measure, it may be necessary
to convert the cubic units of measure to a
volume measure, such as gallons. The most
common conversion factors and examples of
their use are given in Figure 4-24. English-
metric conversion factors are provided in the
Useful Information section.
Chapter 4 Mathematics for Plumbers
95
Figure 4-19. To determine the travel length, measure
the run distance with the 45° offset scale.
Travel
Run
45° Offset scale
Standard English rule
7.07″ Travel
5″ Run
Figure 4-20. This formula can be used to compute
the area of a rectangular surface.
8′
4′
Area = Length × Width
Area = 8′ × 4′
Area = 32 square feet
Figure 4-21. Formula for computing the area of a
circle.
8′
Area = πr2
π = 3.14
r = Radius = 1∕2 diameter
Since the diameter is 8′, the radius is 4′.
Therefore,
Area = 3.14 × (4)2
= 3.14 × 16 square feet
= 50.24 square feet
or
Area = .7854d2
Area = .7854 × (8)2
= .7854 × 64 square feet
= 50.24 square feet