View models at a 1:1 scale

True scale (or 1:1 scale) means that a 10 centimeter long object appears as 10 centimeters long when measured on the screen with a measuring tape.

Calibrate the view to be 1:1

Choose View > View 1:1 > Calibrate 1:1 ❒.
The option box opens, and a distance measurement (red line) appears in the current orthographic window.

NoteThis also works in the Perspective window if Perspective is turned off in the Viewing Panel, and one of the preset orthographic views (horizontal or vertical arrows) is clicked in the Viewing Panel. (See Use the view panel.)
Dolly in/out if necessary to have the distance measurement fill up most of your window.
Use a real ruler or measuring tape to measure the true length of the distance measurement on the screen.
Enter this value as the Displayed Length in the option box.
Press the Calibrate button in the option box.

Switch to the 1:1 view

Choose View > View 1:1 > Toggle 1:1 to set and lock your view to true scale.
A 1:1 label appears in the window title bar to indicate that you are in true scale mode.

NoteDollying in or out of the view is not be possible while in a true scale view.
Choose View > View 1:1 > Toggle 1:1 again to toggle back to regular viewing mode.