Calculating the Scale Factor

With AutoCAD LT, you draw at true size using a convenient unit convention (as described in Specifying Units of Measurement) and then set a scale when you are ready to plot.

Although you do not specify the scale of your drawing until you plot, you can enter in advance the scaled size for

• Text
• Dimensions
• Noncontinuous linetypes
• Hatch patterns
• Views (in floating viewports only)

Scaling these elements ensures that they are at the correct size in the final drawing.

Within model space, if you use the Quick Setup or Advanced Setup wizard when you open a new drawing, AutoCAD LT adjusts many of the scale factors to be appropriate for the world size, or limits, you specify. However, you should calculate the exact scale factor by converting the drawing scale to a ratio of 1:n. This ratio compares plotted units to drawing units.

For example, if you draw at a scale of 1/4 inch = 1 foot, you would calculate the scale factor 48 as follows:

1/4" = 12"
1 = 12 x 4
1 = 48

Using the same calculation, the scale factor for 1/8 inch = 1 foot is 96, and the scale factor for 1 inch = 20 feet is 240.

If you are working in metric units, you might have a sheet size of 210 x 297 mm (A4 size) and a scale factor of 20. You calculate drawing limits as follows:

210 x 20 = 4200 mm
297 x 20 = 5900 mm

EXAMPLE: Sample Architectural Scale Factors for Text Sizes in Model Space

Once you establish the scale factor, you can use it to set text height, dimension sizes, linetype scale, hatch patterns scale, and viewport scale. When the drawing is complete, you can plot it at any scale, or you can plot different views of your drawing at different scales.

Applying Scale Factors

• Text. Set the text height when creating text or by setting a fixed text height in the text style (STYLE). The text height for text created in model space should be multiplied by the scale factor. Text created in paper space should be set to true size (1:1).
• Dimensions. Set the dimension scale in a dimension style (DDIM) or with the system variable DIMSCALE.
• Linetypes. Set the scale for noncontinuous linetypes with the system variables CELTSCALE and LTSCALE. For objects created in floating viewports, use the system variable PSLTSCALE.
• Hatch patterns. Set the scale for hatch patterns in the Boundary Hatch dialog box (BHATCH), or with the system variable HPSCALE.
• Views. For floating viewports, use ZOOM xp, where xp is the scale (the inverse of the scale factor) of the view.

For more information on setting values for these elements depending on whether plotting will be done from model space or paper space, see Creating the Drawing Layout.