4.2.2.1: Prelude to Scales

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Use scale rulers to determine actual dimensions from drawings

Scale drawings are accurate and convenient visual representations made and used by engineers, architects, and people in the construction trades. The accuracy is achieved because the drawing is proportional to the real thing. The convenience comes from the size of the drawing. It is large enough to provide the desired detail but small enough to be handy.

The flexibility to draw proportionally in different sizes is provided by scales. For the purposes of representation, we will only be concerned with reduction scales. Reduction scales make the drawing smaller than the object. The kinds of rulers we will be discussing for making scaled drawings are the architect’s scale shown in Figure 1.

Architect’s scale rulers

The scale of the drawing is always written on the drawing, unless the drawing is not drawn to scale. In the latter case, this will be indicated by the “not to scale” abbreviation (NTS). The scale is the ratio of the size of the drawing to the object. For drawings smaller than the object, the ratio is that of a smaller distance to a larger one.

The architect’s scales use ratios of inches to a foot. One of the most common architect’s scale used is 1/4 inch to the foot, written on drawings as:

Scale 1/4" = 1'-0"

This means that a line 1/4" long on the drawing represents an object that is one foot long in real life. At the same scale, a line 1½" long represents an object 6' long, because 1½" contains 6 quarter-inches.

Figure 2 lists the scale ratios used for building plans and construction drawings in both metric and the approximate equivalent architectural scale ratios.

Type of Drawing	Imperial Equivalents and Ratios		Use
Sketch plans	1/16" =1'-0"	1:192	To show the overall design of the building To indicate the juxtaposition of the rooms and locate the positions of piping systems and components
Ground Plans	1/8" =1'-0"	1:96
Design Drawings	1/4" =1'-0"	1:48
Construction details	1/2" =1'-0" 1" = 1'-0" 3" =1'-0" Full size	1:24 1:12 1:4 1:1	To show the detail of system components and assemblies