The Dimension tool lets you place permanent dimensions on components in your project or family. You can select from aligned, linear (horizontal or vertical projection of a component), angular, radial, diameter, or arc length permanent dimensions.
To view a dimension value after placing it, select one of the components that it references.
Before placing dimensions in Revit, you may want to edit the properties for dimensions and predefine aligned, linear, angular, radial, diameter, and arc length dimensions.