In ArcGIS Pro, you can display the map at any scale. You can also set up a series of desired map scales that allow you to select a scale from a list. The scale list is located at the bottom of each view. Every view has its own independent scale. In 3D views, the scale list refers to the camera's height above the ground elevation surface.
Scales display in one format only, but you can enter a scale in a different format and it will be converted to the display format. For example, if the scales in the list display as relative fractions but you enter 1 cm = 1.5 km, the application converts this to 1:150,000.
Customize the map scale list
You can customize the map scale list that appears throughout your project. When you click Customize from the scale list, the Scale Properties dialog box appears. Here you can build your own map scales by adding or deleting from the list, setting scale alias names, importing an external list, saving changes to your list, or sharing it with others. In 2D, this list is shown on the Standard Scales tab, and in 3D the list is shown on the Standard Heights tab.
Share a map scale list
To share your map scale list with others, click Save on the Scale Properties dialog box.
To make your current set of map scales the default used in all your projects, click the Set As Default button on the Standard Scales tab for maps and the Standard Heights tab for scenes.
Load a map scale list
To reset your active map to use your default scales, click Load > User Profile Default Scales.
To reset your active map to use the Esri-provided default scales, click Load > Factory Default Scales.
Scale aliases
You can optionally define alias values for scales in your map scale list. To set an alias for a particular scale, enter the description in the Alias column on the Standard Scales (2D) or Standard Heights (3D) tab on the Scale Properties dialog box. Choose how you want your scale list presented in the project by choosing a display mode from the Display drop-down list. The map scale lists the following display options:
- Scale: For example, 1:1,000
- Alias: For example, Engineering Scale
- Scale (Alias): For example, 1:1,000 (Engineering Scale)
- Alias (Scale): For example, Engineering Scale (1:1,000)
If a scale does not have an alias, it uses the scale value.
Zoom to predefined scale list
You can limit zooming in a map or scene by specifying a predefined scale list and checking the Only display these scales when zooming check box. When this box is checked, zooming is limited to the scales listed on this dialog box.
Zooming to a predefined scale list applies to navigation methods that step progressively, such as the following:
- Rolling the wheel button
- Clicking the Fixed Zoom In
and Fixed Zoom Out 
buttons in the Navigate group on the Map tab - Pressing the Plus sign or Minus sign keys on your keyboard
It also applies to interactive methods such as continuous zoom using the right mouse button with the Explore tool 
. It does not apply when zooming to a bookmark.
Scale formatting
To set how map scales appear in 2D, use the Scale Format tab on the Scale Properties dialog box.
Scale formats
There are many ways to enter scale values:
Type a number with or without comma separators.
Type 1: and a number.
Paste values into the box.
Type a relative scale (for example, 1 cm = 100 m or 1 in = 1 mi).
The 1: prefix can be present or absent (for example, 1,000,000).
A hyphen (-) or the word to can be used as the separator in place of a colon (:).
Commas used for separating thousands can be present or absent (for example, 1,000,000, or 1000000).
The values in absolute scale expressions can be specified in reverse order (for example, 5 mi to 1 in).
The number one can be given as a number or a word (for example, One inch = 5 miles).
The following unit abbreviations can be used: in, pt, ft, yd, mi, nm, mm, cm, m, km, dd, dm.
Plurals can be used or not (for example, mile or miles).
Recently entered scales are saved as part of the scale list, but are only saved for the active session. To save these values, you must manually reenter them using the Scale Properties dialog box and add them to the current default list of scales. Click Customize to access scale properties.
Two additional scale options
When specifying a scale, such as setting a layer's visibility range, you may notice <None> and <Current> as the listed options.
<None>—Choose this option to clear the scale so that no scale is used. You can also type 0, none, or <None>.
<Current>—If you choose this option, the current scale of the active view is automatically inserted into the field.
Map reference scale
Reference scales are used to fix the size for symbols and text to draw at the desired height and width at the referenced map scale, for example, if you want the detail in your map to look the same on-screen as when you print it. When a reference scale is set, all feature symbology, labels, and graphics are scaled relative to the reference scale, therefore symbols appear the same size relative to surrounding data as you zoom in and out. When a reference scale is not set, symbols appear smaller relative to surrounding data as you zoom in and larger relative to surrounding data as you zoom out.