The size of a drawing may be full size, the actual size of the object, or it may be larger or smaller than the object. The scale chosen depends on the size of the object and the size of the sheet of paper you will use. For example, a machine part may be drawn half size, a building may be drawn 1/96th size, or a circuit card may be drawn twice size.

Measuring scales used in technical drawings are (a) Architects' Scale, (b) Engineers' Scale, and (c) Metric Scale. A diagram of each scale is shown below.

The architect's scales shown below are the triangular style.   You will notice that the triangular scale has six sides which will accommodate 11 different scales.  These scales are a full scale of 12" graduated 16 parts to an inch, and 10 other open-divided scales which include ratios of 3/32, 1/8, 3/16, 1/4, 3/8, 1/2, 3/4, 1, 1 1/2, and 3.  Two scales are located on each face.  One scale reads from left to right.  The other scale, which is twice as large, reads from right to left.  For example, the 1/4' scale and the 1/8" scale are placed on the same face but read from different directions.

When measuring with the architect's scale, start the with the zero line, with not with the fully divided section.  Always start with the number of feet you wish to measure and then add the additional inches in the subdivided area.   For example, in the figure below item (c) on the 1/4 ratio, the distance of 7'-2" is derived by measuring from the line 7 to 0, then 2" past zero.   Note, each line in the subdivided part is 1".

STANDARD SCALES:

1/16" = 1' - 0"
1/8" = 1' - 0"
1/4" = 1' - 0"
3/8 = 1' - 0"
1/2 = 1' - 0"
3/4 = 1' - 0"
1" = 1' - 0"
1 1/2" = 1' - 0"
3" = 1' - 0"

The civil engineer's scale is often used to plot plans, surveys, landscapes and mechanical drawings.  Each scale divides the inch into decimal parts.  These parts are 10, 20, 30, 40, 50 and 60 parts per inch (see figure below).  Each one of these units can represent any distance, such as an inch, foot, yard, or mile, depending on the final drawing size.

STANDARD SCALES:

1" = 10'
1" = 20'
1" = 30'
1" = 40'
1" = 50'
1" = 60'
1" = 100'

The metric scales shown below are used in the same manner as the architect's scale is used to prepare reduced-size drawings.  Metric scales, however, use ratios in increments of 10 rather than fractional ratios.  The ratio chosen depends on the size of the drawing compared to the full size of the object.   The image below shows some of the common metric ratios used.

STANDARD SCALES:

1:1 FULL SIZE
1:2 HALF SIZE
1:5 FIFTH SIZE
1:10 TENTH SIZE
1:20 TWENTIETH SIZE
1:50 FIFTIETH SIZE

SCALE SELECTION

If your not sure which scale to use, a simple calculation will help you decide.   For example, you are required to draw a large building on a "C" size sheet of paper (18"x24").  You will allow a 2" border on all four sides of the paper for clearance.  with this border the available area your left with is 16"x22"(see figure below).  The required building to be placed on the sheet is 100'x60' (see figure below). 

Use the following equation to compute the required scale:

                                            Scale Factor = Desired Drawing Size/Paper Size

(Remember to convert feet to inches by multiplying by 12")

                                                        Scale Factor = [(100')(12")]/16" = 75

Since a scale factor of 75 is not a standard scale factor, you would select the next larger standard scale factor of 96 (scale of 1/8"=1'-0") and use it to draw your building.