I’m working with a notation software and I would need to space certain graphical elements evenly within a predetermined space (e.g.: I set a 5cm space and I have 5 elements, they need to be precisely 1cm from each other), something that the software cannot do on its own (that is, without printing on paper, measuring, then moving the objects, then printing again and so on...).

The ideal solution would be to have a floating ruler on the screen or a superposed grid similar to millimetric paper that would still allow click-through (i.e.: interaction with the program below it).

Is there an app that provides this tool?

Thank you very much

  • 1
    I’m not sure if OmniGraffle can do this, but it was the first app that popped into my head as a possibility.
    – TJ Luoma
    Aug 21, 2019 at 16:25

7 Answers 7


I've used Free Ruler for Mac OS X in the past. I'm amazed that still works just fine. However, it does not allow click-through.

  • 1
    what a beautifull simple little piece of software <3
    – Hans Dash
    Jun 9, 2022 at 12:25
  • Works great, and it does inches/cm!
    – Joe B
    Sep 22 at 16:42

Not Exactly a ruler app but using the built in Command+Shift+4 screenshot tool can help too.

  • How exactly would the built-in screenshot help to solve the problem described in the question?
    – nohillside
    Jan 29, 2022 at 8:46
  • 2
    When you are defining the area to select, it shows the dimensions of the selected area. See this nice demo: ctrl.blog/entry/how-to-osx-screen-shot-ruler.html
    – SteveDonie
    Jan 31, 2022 at 22:49
  • 1
    This would be really a nice option.
    – Neela
    Aug 24, 2022 at 5:28
  • 2
    @Neela Yes It can be handy sometimes to make quick check specially.
    – Asme Just
    Aug 24, 2022 at 11:38
  • This! It's quick, built-in, free, and always at hand. Got the job done for me. Thank you!
    – WhatHiFi
    Oct 5 at 15:05

iconfactory's xScope

enter image description here

Powerful on-screen rulers for precise pixel measurements that include scaling, rotation, and edge snapping.

xScope’s rulers can be used to measure any on-screen element, including the distance and angles between objects. Holding down the Control key while dragging the ruler near an on-screen object causes the edges and ends of the ruler to “snap” into place, making measuring quick and easy. Additionally, the Ruler tool includes calipers which can be toggled on or off and used for outside measurements.

Not sure if non-pixel measurements are possible.

  • 1
    This can only display measurements in Screen pixels or Window points. Aug 21, 2019 at 13:27

Have a look at:

Ondesoft Screen Rulers for Mac

Easy, powerful and accurate virtual screen rulers for your Mac

Ondesoft Screen Rulers is a highly configurable measuring utility for Mac with many intuitive features, enable you to measure objects quickly and precisely on your Mac screen in Pixels, Inches, Picas, Centimeters and multiple customizable units according to your need. It can measure square areas, diagonals and display angles.

  • Online measuring tool to measure the dimensions of any objects on Mac.
  • Easy protractor enables you to measure angles in radians or degrees with Ondesoft Screen Rulers.
  • Detail Window provides you a magnifier and pixel value for accurate measurements.
  • Logger Window serving as your personal notebook can remember all the detailed measurements data history.
  • Customize keyboard shortcuts, ruler colors and transparency settings according to your preference.

Has a free trial, $9.95 USD to buy.

Note: I am not affiliated with the developer of this software. Simply a Google search.


Free Ruler has been updated for macOS Catalina. It’s free and open-source: http://www.pascal.com/software/freeruler/

Then there’s PixelSnap for $40 (that’s $10 cheaper than xScope and comes with seemingly superior dimension measurement engine).

  • Unfortunately it doesn't work in Mac OS Ventura - warning appears that it can't be checked for malicious code and it needs to be updated. Bummer.
    – dunxd
    Sep 15 at 9:22

I have found these two free utilities.
They kind of do what I need but are very basic so anything more would be overkill for them.
- Red Line Tools.
- Ruler on Call EZ

Both available on the Mac App Store.

  • 1
    Red Lines Tools is both free and fantastic. Exactly what I needed for making measurements in my app's UI. Thanks!
    – nonbeing
    Oct 17, 2020 at 15:00

Shottr is a screenshot measurement and annotation tool

One of its features: Use it as a Screen Ruler

brew install --cask shottr

enter image description here

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