Subject: Understanding scale factors

Instead of drawing to a particular scale, you draw everything in the program full-size. Although it’s a good idea to keep your scale factor in mind when setting up a draw­ing, you don’t need to set the scale until you print it. For example, when you draw a mechanical part 40 inches in length with CADdirect, you actually draw it as 40 inches, rather than applying a scale factor as you draw. When you print your drawing, you can assign the scale at which the drawing is to print.          

Scale, however, does affect the way a few elements such as text, arrows, or linetypes  print or plot and even display in your drawing. You can set up annotation scaling to control the scale of entities such as text, arrows, and linetypes, or you can make man­ual adjustments when you first set up your drawing so that annotations print and dis­play at the correct size. For example, when you draw text, you need to determine the text size so that when you print it later at a particular scale, the text height is correct.     

After you determine the eventual scale of your finished drawing, you can calculate the scale factor for the drawing as a ratio of one drawing unit to the actual scale unit represented by each drawing unit. For example, if you plan to print your drawing at
1/8 = 1-0, your scale factor ratio is 1:96 (1/8 = 12 is the same as 1 = 96). If you want your printed scale to be 1 inch = 100 feet, your scale factor ratio is 1:1200.        

The following table shows some standard architectural and engineering scale ratios and equivalent text heights required to create text that measures 1/8-inch high when you print the drawing at the specified scale.        

Standard scale ratios and equivalent text heights


Scale factor

Text height

1/16” = 1’-0”



1/8” = 1’-0”



3/16” = 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”



1” = 10’



1” = 20’



1” = 30’



1” = 40’



1” = 50’



1” = 60’



1” = 100’



You can use these scale factors to predetermine the size of your drawing to make sure that it fits on a specific size paper when you print it. You control the size of your drawing by the drawing limits. To calculate the drawing limits to match the size of your paper, multiply the dimensions of your paper size by your scale factor.        

For example, if the paper you use to print measures 36 inches x 24 inches and you print your drawing at 1/8 = 1-0 (in other words, using a scale factor of 96), the size of your drawing measured in drawing units is 36 x 96 (or 3,456 units) wide and 24 x 96 (or 2,304 units) high.

Keep in mind that you can print the finished drawing at any scale, regardless of the scale factor you calculate. You can also print on paper of a different size and use the Layout tabs to create different views of your drawing and to position and scale those views differently. The scaling factor is not related to the size of the entities you draw; it simply provides a preliminary guide to help you establish the text height and draw­ing limits when you begin your drawing. You can change the text height and drawing limits at any time.

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