Aequo: On-Screen Measurements

A lightweight utility designed to help you take length and angle measurements of objects on your screen.

A very versatile tool to quickly take measurements on photos, videos, or anything else.
Stupendo, comodisssimo per lavorare, leggero, semplice ed effice. Bello e funzionale Compimenti ai ragazzi che l'hanno scritto.
I found this simple app very useful when sizing images that are odd shapped in a Word document. I used to put a physical ruler onto my screen (sounds crazy I know, but it did work). This app makes it easy. So far, so good.
Mick from Dry Plains


  • Grid Tool
    Show an inch or centimeter grid overlay
  • Linear Measurement Tool
    Find the distance between two points on your screen
  • Linear Conversion Factor
    Apply a conversion factor to linear measurements to scale on-screen units to real-world units

  • Protractor Tool
    Overlay your screen with a movable, zoomable protractor
  • Angle Measurement Tool
    Find an angle between three points on your screen
  • Pen Tool
    Annotate or doodle over your measurements

The Details

Feature Description Shortcut
Inch Grid Add a grid overlay with major grid lines every inch and minor grid lines every eighth of an inch ⌘G
Centimeter Grid Add a grid overlay with major grid lines every centimeter and minor grid lines every millimeter ⇧⌘G
Protractor Display a protractor. Move the protractor around the screen by clicking and dragging, scale it up or down by scrolling, and rotate it by holding option (⌥) and scrolling. ⌘P
Linear Measure Tool Click once to start a linear measurement at the reticle; click again to complete the measurement ⌘L
Slope Tool Select any two existing linear measurements with the reticle to find their slopes and an angle between them ⌘I
Live Angles Toggle whether angles between existing and in-progress linear measurements are shown ⌥⌘L
Linear Conversion Factor Supply a ratio between a real-world distance and an on-screen one (say, via a ruler in a photo) to automatically convert linear measurements ⇧⌘L
Angle Measure Tool Click once to define the vertex of an angle at the reticle, again to set a second point, and a third time to complete the angle ⌘N
Keep Past Measurements Toggle whether past measurements are cleared before starting another one ⇧⌘K
History Show a copy-able log of all measurements made in the current session ⇧⌘H
Undo/Redo Undo or repeat past measurements (to remove annotations made with the Pen, the Eraser can be used instead) ⌘Z/⇧⌘Z
Pen Tool Use your cursor to draw free-form in the Aequo window ⌘D
Eraser Tool Erase strokes made with the Pen Tool only (not measurements) ⌘E
Pen Color Change the stroke color of the Pen Tool ⌘1 through ⌘8
Clear Menu Clear past measurement history, linear or angle measurements, annotations, or everything in the Aequo window N/A
Offset Cursor Crosshairs Toggle whether the measurement reticle is located at the cursor, or offset north-west slightly ⇧⌘C
Toggle Background Contrast Choose whether the Aequo overlay has a light or dark tint (e.g., to provide better contrast with the screen underneath the window) ⇧⌘B
Increase Window Transparency Increase transparency of the main window in steps of 10% ⇧⌘=
Decrease Window Transparency Decrease transparency of the main window in steps of 10% ⇧⌘-

Other Tips

  • The escape (ESC) key can be used at any time to cancel an in-progress measurement.
  • Hold shift while making a linear or angle measurement to snap to the closest 15° angle increment.

Aequo for Education

Teachers or educational institutions can get a 50% discount by using the App Store Volume Purchase Program. Visit to learn more.