Scale factors
CAD Scale Factors: Chart, Viewport XP Values, and Text/DIMSCALE Settings
CAD scale factors connect a full-size model to its plotted size. Use the charts below to find the factor for an architectural or engineering drawing, enter its reciprocal as a viewport XP value, and size non-annotative text and dimensions for the plot.
Unit assumption: model space and paper space both use inches throughout these charts and examples. Manual annotation scaling applies to non-annotative objects. Annotative text and dimensions use annotation scales instead; do not multiply their sizes again.
What Is a CAD Scale Factor?
A CAD scale factor tells you how many full-size drawing units correspond to one plotted unit when both use the same units. For a drawing at 1/4" = 1'-0", divide 12 inches by 1/4 inch: the factor is 48.
Keep the factor and the display ratio separate. The factor is 48, while the paper-to-model ratio is 1:48. AutoCAD uses the reciprocal, 1/48xp, to display that reduction in a layout viewport. Entering 48xp would enlarge the view instead.
Architectural CAD Scale Factor Chart
This CAD scale factor chart lists common US architectural scales with their factors, reciprocal XP values, and decimal equivalents. Choose the intended drawing scale in the first column, then read across for the matching settings. The guide to architectural scale factors shows how each factor is derived from its drawing scale.
| Drawing Scale | Scale Factor | Viewport XP Value | Decimal Scale |
|---|---|---|---|
| 1/32" = 1'-0" | 384 | 1/384xp | .03125" = 1'-0" |
| 1/16" = 1'-0" | 192 | 1/192xp | .0625" = 1'-0" |
| 3/32" = 1'-0" | 128 | 1/128xp | .09375" = 1'-0" |
| 1/8" = 1'-0" | 96 | 1/96xp | .125" = 1'-0" |
| 3/16" = 1'-0" | 64 | 1/64xp | .1875" = 1'-0" |
| 1/4" = 1'-0" | 48 | 1/48xp | .25" = 1'-0" |
| 3/8" = 1'-0" | 32 | 1/32xp | .375" = 1'-0" |
| 1/2" = 1'-0" | 24 | 1/24xp | .50" = 1'-0" |
| 3/4" = 1'-0" | 16 | 1/16xp | .75" = 1'-0" |
| 1" = 1'-0" | 12 | 1/12xp | 1" = 1'-0" |
| 1-1/2" = 1'-0" | 8 | 1/8xp | 1.5" = 1'-0" |
| 3" = 1'-0" | 4 | 1/4xp | 3" = 1'-0" |
| 6" = 1'-0" | 2 | 1/2xp | 6" = 1'-0" |
| Full size (1:1) | 1 | 1xp | 12" = 1'-0" |
Engineering Scale Factor Chart
For engineering scales written as 1" = X feet, calculate the factor as 12 × X. This converts the model distance from feet to inches before comparing it with one plotted inch. For example, 1" = 100' gives 12 × 100 = 1200.
| Drawing Scale | Scale Factor | Viewport XP Value |
|---|---|---|
| 1" = 10'-0" | 120 | 1/120xp |
| 1" = 20'-0" | 240 | 1/240xp |
| 1" = 30'-0" | 360 | 1/360xp |
| 1" = 40'-0" | 480 | 1/480xp |
| 1" = 50'-0" | 600 | 1/600xp |
| 1" = 60'-0" | 720 | 1/720xp |
| 1" = 70'-0" | 840 | 1/840xp |
| 1" = 80'-0" | 960 | 1/960xp |
| 1" = 90'-0" | 1080 | 1/1080xp |
| 1" = 100'-0" | 1200 | 1/1200xp |
| 1" = 200' | 2400 | 1/2400xp |
| 1" = 400' | 4800 | 1/4800xp |
| 1" = 500' | 6000 | 1/6000xp |
These CAD scale factors assume an inch-based model. Check the drawing's units before using the XP column; a model drawn in feet needs a different model-to-paper conversion.
How to Set Viewport Scale with XP
To set the viewport scale factor in AutoCAD, activate the layout viewport, run ZOOM, and enter the reciprocal factor followed by xp.
- In paper space, double-click inside the viewport to enter model space through it.
- Type Z and press Enter to run ZOOM.
- Enter the XP value from the chart. For 1/8" = 1'-0", enter 1/96xp with model and paper units both in inches.
The XP suffix makes the zoom value relative to paper-space units. For example,.5xp displays the model at half size; it is not the same as 1/2" = 1'-0", which needs 1/24xp under these unit assumptions.
Lock the viewport scale after setting it. Stretching its border changes the visible area, not the scale of the view inside it.
How to Apply AutoCAD Scale Factors
For non-annotative model-space text, multiply the desired plotted height by the drawing factor. Other settings depend on the object and plotting workflow:
- Text, attributes, and table text: desired plotted height × factor = model-space height.
- Dimensions: for traditional non-annotative model-space plotting, use the factor as DIMSCALE. Layout-based and annotative methods differ, as explained below.
- Linetypes: choose LTSCALE with the linetype definition and intended dash length in mind. It is not automatically equal to the drawing factor.
- Hatches: set hatch scale for the chosen pattern. Architectural patterns with the AR prefix commonly use the drawing factor.
- Blocks: geometry is usually drawn full size. Text or attributes within a block may need annotation scaling; do not resize full-size geometry merely to make its text readable.
Use these rules to select the setting, then check the plotted output. The worked example below shows the text-height calculation.
Dimensioning in Model Space and Paper Space
Model-space plotting uses a manual dimension scale in the traditional workflow; layout-based dimensioning can account for viewport scale automatically. Choose the method before setting DIMSCALE.
- Dimension in model space for model-space plotting. Set DIMSCALE to the inverse of the intended plot scale. A plot scale of 1/4 needs DIMSCALE = 4. This 1:4 ratio differs from the architectural notation 1/4" = 1'-0", which is 1:48.
- Dimension in model space for paper-space plotting. In the non-annotative layout-scaling method, set DIMSCALE to 0 to scale dimensions for display in a layout viewport. Separate dimension layers can keep dimensions for one viewport hidden in the others.
- Dimension in paper space. Associative dimensions attached to model-space objects account for the viewport's display scale together with DIMLFAC. Nonassociative dimensions need DIMLFAC set manually.
For annotative dimension styles, DIMSCALE is 0 and the annotation scale controls sizing. Do not apply the manual text-height multiplication to annotative dimensions.
CAD Scale Factor Example for 1/4" = 1'-0"
A floor plan at 1/4" = 1'-0" uses a factor of 48 and a viewport value of 1/48xp when model and paper units are inches. For non-annotative model-space annotation:
- Factor: 12 ÷ 1/4 = 48.
- Viewport zoom: 1/48xp.
- Text intended to plot 1/4" high: 1/4 × 48 = 12" in model space.
- DIMSCALE for the traditional model-space plotting method: 48.
Check the result in reverse: 12" of model-space text height × 1/48 = 1/4" on paper. This reciprocal check helps catch a factor entered the wrong way around.
How to Add a Custom Drawing Scale
Use SCALELISTEDIT to add a custom scale to the drawing's scale list. It changes the available scale choices without resizing the model geometry.
To bring changes from the default scale list into the current drawing, use Reset in the Edit Drawing Scales dialog. Scales stored in a template carry into new drawings created from it; user-profile scales are not imported automatically.
For repeat projects, keep the required CAD scale factors in the drawing template so the scale choices are available from the start.