Datum Dimension

Parent page: PCB Dialogs

The Datum Dimension dialog.


This dialog allows the designer to specify the properties of a Datum Dimension object. A datum dimension is a group design object. It allows for the dimensioning of a linear distance of a collection of objects, relative to a single reference object. The first object chosen is the 'base'. All subsequent objects are relative to this first object. The dimension value in each case is therefore the distance between each reference object and the 'base', measured in the default units. The references may be tracks, arcs, pads, vias, text, fills, polygons or components.

For information on how a placed datum dimension object can be modified graphically, directly in the workspace, see Graphical Editing.


The Datum Dimension dialog can be accessed during placement by pressing the Tab key.

After placement, the dialog can be accessed in one of the following ways:

  • Double-clicking on the placed datum dimension object.
  • Placing the cursor over the datum dimension object, right-clicking and choosing Properties from the context menu.


  • Pick Gap - the current pick gap value, which is is the distance between the dimension extension line and the object being dimensioned.
  • Rotation - the angle of alignment of the dimension, measured anti-clockwise in degrees from the horizontal.
  • Text Gap - the current gap between the dimension value text and the extension line.
  • Text Width - the current dimension text stroke width (the "thickness" of the lines used to produce the lettering).
  • Extension Width - the current width for the dimension extension lines.
  • Text Height - the current height of the dimension text characters. The character width used to display or print the text is automatically proportioned to this height. A minimum height of 36mil (0.9mm) will allow the string to be legibly photoplotted.
Quickly change the units of measurement currently used in the dialog between metric (mm) and imperial (mil) using the Ctrl+Q shortcut. This affects the dialog only and does not change the actual measurement unit employed for the board, as determined by the  and  buttons in the Home | Grids and Units area of the main menus.


  • Layer - the layer the dimension is currently assigned to. Dimensions can be assigned to any available layer, click on the list to view and select a different layer, from all those currently defined for the board.
  • Unit - the current unit that is selected for the calculation and display of the dimension value. Choose either Mils, Millimeters, Inches, Centimeters, or Automatic.
The Automatic setting follows the actual measurement unit employed for the board, as determined by the  and  buttons in the Home | Grids and Units area of the main menus.
  • Format - the current setting for the format of the dimension text. Use the associated drop-down to change the format as required. The options listed will depend on the chosen Unit and present based on the actual value for the current dimension. In generic terms, the available options are:
    • None - no dimension text is displayed.
    • Value Only - no units are displayed, only the dimension value (eg. 1220.45).
    • Value and Unit - units are displayed after the dimension value (eg. 1220.45mil).
    • Value and Bracketed Unit - units are displayed in brackets after the dimension value (eg. 1220.45(mil)).
  • Precision - the current setting for the number of decimal places to the right of the decimal point that the dimension will be displayed to. The maximum number of decimal places is 6.
  • Position - the current position of the dimension text. Use the associated drop-down list to choose one of the following options:
    • Aligned - the dimension text will be aligned with the angle of the dimension line.
    • Unidirectional - the dimension text will remain horizontal, irrespective of the dimension alignment angle.
    • Manual - the dimension text will be available for manual placement by the user.
  • Prefix - the current prefix to the dimension value.
  • Locked - enable this option to protect the dimension from being edited graphically.
An object that has its Locked property enabled cannot be selected or graphically edited. Double click on the locked object directly and disable the Locked property, to graphically edit the object.
  • Suffix - the current suffix to the dimension value.
  • Sample - this field presents a sample of how the dimension text will appear, in accordance with specified Format, and any defined Prefix and/or Suffix.

Select TrueType Font

  • Font Name - use this field to choose the required TrueType font. The drop-down list is populated with TrueType and OpenType (a superset of TrueType) fonts found in the \Windows\Fonts folder. Note, the list will only include entries for detected (and uniquely named) root fonts. For example, Arial and Arial Black will be listed but Arial Bold, Arial Bold Italic, etc will not. Use the Bold and Italic options to add emphasis to the text.
  • Bold - enable this option to make the dimension text bold.
  • Italic - enable this option to make the dimension text italic.


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