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SAMSON provides the Measure editor that allows you to measure distances, bond lengths, angles, and dihedrals. You can find in the left-side menu in the viewport (Measure editor) or invoke it using the Ctrl/Cmd + M shortcut.

You can use the Measure editor as follows:

  • Click on a bond to toggle displaying its length.
  • Click on two atoms to display the distance between them.
  • Click on three atoms to display the angle between them.
  • Click on four atoms to display the torsion between them.

To save the displayed data as a label in the document, press Enter.

Measuring example

If a measurement is not saved in the document as a label, it acts as a temporary one that will always be shown no matter the zoom level but it will disappear once the next measurement is done - you can have only one temporary measurement, if you want to have more than one, then you need to save it as a label by pressing Enter.


If you save your document in one of the SAMSON file formats (.sam or .samx), labels with measurements will be saved as well.

If the label was saved in a document, you can access the atoms associated with the measurement by selecting a label and opening the Inspector. See the Measure group in the image below. The atom-atom distance measurement, if saved as a label, has additional measurements shown in the Inspector for projections on the planes.

Atom-atom distance projections

Other types of available measurements are labels for formal and partial charges of atoms. They can be added as labels via a context toolbar for selected nodes: Label editor Label > Add label to... > Atoms (formal charges).

Add atom formal charge label


Measurements are automatically updated (in the Viewport, Document view, and in the Inspector), when the associated atoms change their positions or charges. So, you can follow the measurements, while using Move editors or interactive minimization.

Automatic update of measurements


Prerequisites: Please refer to the Inspecting section to learn how to inspect nodes in SAMSON.

Measurements saved as labels in the document act exactly as labels: their visibility changes depending on the zoom level, and you can change their font, color, and offset. See the Labeling section for more information on how to modify labels.

For measurement labels you can also modify colors of distance lines and angle planes using the Inspector (see "Line color", "Angle color", "Planes color").

Colorization of an atom-atom distance line and text

Colorization of a torsion angle

To reset to the default colors, double-click on the associated text in the Inspector as shown on the image below.

Reset line color

To reset the text color, click on X (clear) button next to the Text color as shown on the image below.

Reset text color

You can also specify the font for each label in the Inspector.

Set label font in Inspector


You can specify the font for labels per label directly in the Inspector or for all the labels, for which the font has not been specified directly, in Preferences > Rendering > Labels and change it there. There you can also modify the number of decimal places for angles and distances shown in labels which is used for labels created using the Measure editor.

The labels preferences

See also: Labeling, Selecting, Inspecting.