July 19, 2009September 23, 2014 by Tim Moore

Centering Windows in Mac OS X with AppleScript

I can be a little OCD with the windows on my screen. I tend to line them up at the edges or try to center them in the display. Maybe it’s a bad habit, but it’s one I’m probably not going to shake any time soon, so the least I can do is try to avoid wasting too much time on it.

Update, 23-Sep-2014: I still get occasional questions about this post, but in truth, I haven’t used this script in years. These days, my solution of choice is Spectacle, a free and open source app that can center windows and do a lot more—including various types of tiling, and moving windows from one screen to another—with configurable keyboard shortcuts for everything. There are a lot of other alternatives out there, but this one doesn’t cost anything and is pretty capable.

Update, 15-Nov-2010: This continues to be a fairly popular post, which a lot of people seem to come across through search engines. See the comments below for tips about ensuring that the window size doesn’t change, and for centering vertically as well. I’ve also noticed that this fails on multi-display setups, centering between the two screens instead of on the current screen. I’ll try to come up with a fix for that.

I found an AppleScript on GitHub for centering the frontmost window. It didn’t do quite what I wanted, so here’s my slightly-modified version, which will center the window in your screen horizontally without changing the vertical position or size.

tell application "Finder"
	set screenSize to bounds of window of desktop
	set screenWidth to item 3 of screenSize
end tell

tell application "System Events"
	set myFrontMost to name of first item of ¬
		(processes whose frontmost is true)
end tell

try
	tell application myFrontMost
		set windowSize to bounds of window 1
		set windowXl to item 1 of windowSize
		set windowYt to item 2 of windowSize
		set windowXr to item 3 of windowSize
		set windowYb to item 4 of windowSize
		
		set windowWidth to windowXr - windowXl
		
		set bounds of window 1 to {¬
			(screenWidth - windowWidth) / 2.0, ¬
			windowYt, ¬
			(screenWidth + windowWidth) / 2.0, ¬
			windowYb}
	end tell
end try

Paste this into Script Editor or download the script file. Put the file in ~/Library/Scripts. Make sure you’ve got the Script menu turned on in the AppleScript Utility application. It will show up in there, and should work in most Mac applications.

I have found a couple of limitations. It doesn’t seem to work at all with Firefox, which doesn’t have very complete AppleScript support. It’s likely that there are other applications out there with missing or incomplete AppleScript support that this won’t work for either. The second problem is that there’s a bug in the Terminal application that moves the window upwards, even though the script is written in a way that’s supposed to preserve the vertical position. It would be possible to work around this, but I decided that it didn’t bother me enough to clutter up the code. If you want a workaround, post a comment and I’ll give it a shot.

The original script doesn’t specify a license, so I hope it’s OK to modify and share it. I figure that, since it’s published on GitHub, and the author releases a lot of open source code under very liberal licenses, that he’s probably not intending to keep very tight control over it. My changes are offered to the public domain.

I’m just as obsessive with making sure objects are lined up straight on my (real life) desk top. Sadly, AppleScript can’t help me there.

27 Replies to “Centering Windows in Mac OS X with AppleScript”

metanoize says:

July 19, 2009 at 11:26 pm

have you see SizeUp http://www.irradiatedsoftware.com/

Reply
1. Tim Moore says:
  
  July 20, 2009 at 12:37 am
  
  I hadn’t, but to be honest most of the features other than centering don’t really appeal to me. This script works well enough for that.
  
  Reply
Stakker says:

November 9, 2009 at 6:47 am

Very cool, cheers! (I share the same alignment “problem” 🙂
I use Spark to launch the script with a keyboard shortcut myself.

However, the script can actually change the horizontal window size by one pixel.

This is noticeable with Pages if you size the window so that it’s exactly the width of the page (horizontal scroll bar disappears but no background gray appears yet). The script can sometimes make the window 1 pixel wider or narrower depending on the width of the window. Perhaps something to do with odd/even numbers?

Yes, one pixel. But we’re already in freaky obsession territory here! 🙂 (In pages the one pixel is very noticeable since it makes an ugly dark line appear into the margin, instead of smooth white.)

Reply
1. Tim Moore says:
  
  November 20, 2009 at 8:30 pm
  Good catch, Stakker,
  
  That’s because windows with an odd-numbered pixel-width can’t be perfectly centered on a screen with an even number of pixels. Fractional pixel values get rounded automatically.
  
  If you want more control over the rounding, you can change this part:
```
    set bounds of window 1 to {¬
        (screenWidth - windowWidth) / 2.0, ¬
        windowYt, ¬
        (screenWidth + windowWidth) / 2.0, ¬
        windowYb}
```
  to something like this:
```
    set bounds of window 1 to {¬
        round ((screenWidth - windowWidth) / 2) rounding as taught in school, ¬
        windowYt, ¬
        round ((screenWidth + windowWidth) / 2) rounding as taught in school, ¬
        windowYb}
```
  It’s kind of wordy, but it tells AppleScript to always round .5 up. Normally, it rounds .5 towards the nearest even number.
  
  You can see full documentation for the different rounding options in the AppleScript 2.1 Help: round document on Apple’s site.
  Reply
Stakker says:

November 22, 2009 at 12:41 pm

Well, that did the trick!

Gotta love AppleScript syntax 🙂

Thank you for bothering to help. My life is in order again! 😉

Reply
James says:

April 18, 2010 at 12:00 am

Hey there,
good post, extremely useful!
Also check out this page for handy scripts http://www.giacomoballi.com/scripts.html
By the way, Tim, i was just about to point that out…
Good job guys!

Reply
Russ says:

July 13, 2010 at 10:44 pm

I love this script, but I’m new to Macs, and a total noob with scripts, so bear with me…

If you have, for example, two Word documents open, the script will only apply itself to the document that was initially opened. You can’t toggle between windows and apply the script to the second document.

Is there anyway to jig this script so that it will work with multiple windows of the same application after having switched to the second or subsequent document/window?

Reply
1. Tim Moore says:
  
  July 19, 2010 at 1:27 pm
  
  Russ,
  
  Normally it should work with whatever window is frontmost, but I can’t guarantee it will work properly in every application, because it depends on their support for AppleScript. I unfortunately don’t have a copy of Microsoft Word to test with, but if anyone has a solution, please let me know and I’ll update the post.
  
  Reply

Thank you, Tim, this script is incredibly useful for obsessive people like us.

I’m wondering if it would be at all possible to center windows vertically as well? I don’t know AppleScript, and can’t seem to figure this out. Ideally, I’d like my Mail, iTunes, Finder windows, etc. to be centered vertically between the dock and menu bar.

Thanks!

It should be possible to make it center vertically using basically the same approach.

Try this:

tell application "Finder"
	set screenSize to bounds of window of desktop
	set screenWidth to item 3 of screenSize
	set screenHeight to item 4 of screenSize
end tell

tell application "System Events"
	set myFrontMost to name of first item of ¬
		(processes whose frontmost is true)
end tell

try
	tell application myFrontMost
		set windowSize to bounds of window 1
		set windowXl to item 1 of windowSize
		set windowYt to item 2 of windowSize
		set windowXr to item 3 of windowSize
		set windowYb to item 4 of windowSize
		
		set windowWidth to windowXr - windowXl
		set windowHeight to windowYb - windowYt
		
		set bounds of window 1 to {¬
			round ((screenWidth - windowWidth) / 2) rounding as taught in school, ¬
			round ((screenHeight - windowHeight) / 2) rounding as taught in school, ¬
			round ((screenWidth + windowWidth) / 2) rounding as taught in school, ¬
			round ((screenHeight + windowHeight) / 2) rounding as taught in school}
	end tell
end try

Again, thanks so much – I feel SO nice knowing that this is possible; I’ve never even seen AppleScript until today! I eventually figured out how your version worked, and came up with the following:

tell application "Finder"
	set screenSize to bounds of window of desktop
	set screenWidth to item 3 of screenSize
	set screenHeight to item 4 of screenSize
end tell

tell application "System Events" to tell process "Dock"
	set dockSize to size in list 1
	set dockHeight to item 2 of dockSize
end tell

tell application "System Events"
	set screenHeight to (screenHeight - dockHeight)
	set myFrontMost to name of first item of ¬
		(processes whose frontmost is true)
end tell

try
	tell application myFrontMost
		set windowSize to bounds of window 1
		set windowXl to item 1 of windowSize
		set windowYt to item 2 of windowSize
		set windowXr to item 3 of windowSize
		set windowYb to item 4 of windowSize
		
		set windowWidth to windowXr - windowXl
		set windowHeight to windowYb - windowYt
		
		set bounds of window 1 to {¬
			round ((screenWidth - windowWidth) / 2) rounding as taught in school, ¬
			round ((screenHeight - windowHeight) / 2) rounding as taught in school, ¬
			round ((screenWidth + windowWidth) / 2) rounding as taught in school, ¬
			round ((screenHeight + windowHeight) / 2) rounding as taught in school}
	end tell
end try

The two problems with what I’ve got are that Assistive Devices have to be enabled in System Preferences, and it’ll only work with the Dock on the bottom, but I never move mine anyway.

Cheers! 🙂

Axel says:

January 20, 2011 at 4:08 am

Just wanted to say that this was incredibly helpful, as I’m new to Macs and as obsessive-compulsive about placement as you are. Thanks!

Reply
Andrew Goodrick-Werner says:

January 20, 2011 at 4:22 pm

Also, here’s a tip I’ve found to be extremely useful.

You can make this AppleScript a Service that is accessible from any application’s menu in the Menu Bar. Open Automator, create a new Service — setting the options at the top to “no input” and “any application” — drag “Run AppleScript” into the workflow, and paste one of the scripts posted above into the text field. Save the Service, and run it from the Services menu in the Menu Bar.

I prefer this method to having the Scripts menu always visible in my menu bar, since this is the only AppleScript I use regularly.

Reply
1. Tim Moore says:
  
  January 22, 2011 at 9:52 am
  
  Good tip, Andrew. Thanks!
  
  Reply

I found a post on Stack Exchange that links to this post but asks about the issue with the Terminal. It’s just a bug in Terminal’s Apple Events support, but there is a workaround. Here it is:

tell application "Finder"
	set screenSize to bounds of window of desktop
	set screenWidth to item 3 of screenSize
	set screenHeight to item 4 of screenSize
end tell

tell application "System Events"
	set myFrontMost to name of first item of ¬
		(processes whose frontmost is true)
end tell

try
	tell application myFrontMost
		set windowSize to bounds of window 1
		set windowXl to item 1 of windowSize
		set windowYt to item 2 of windowSize
		set windowXr to item 3 of windowSize
		set windowYb to item 4 of windowSize
		
		set windowWidth to windowXr - windowXl
		set windowHeight to windowYb - windowYt
		
		if myFrontMost is "Terminal" then
			set bounds of window 1 to {¬
				round ((screenWidth - windowWidth) / 2) rounding as taught in school, ¬
				round ((screenHeight + windowHeight) / 2) rounding as taught in school, ¬
				round ((screenWidth + windowWidth) / 2) rounding as taught in school, ¬
				round ((screenHeight + windowHeight) / 2 + windowHeight) rounding as taught in school}
		else
			set bounds of window 1 to {¬
				round ((screenWidth - windowWidth) / 2) rounding as taught in school, ¬
				round ((screenHeight - windowHeight) / 2) rounding as taught in school, ¬
				round ((screenWidth + windowWidth) / 2) rounding as taught in school, ¬
				round ((screenHeight + windowHeight) / 2) rounding as taught in school}
		end if
		
		set the result to bounds of window 1
		
	end tell
end try

Andrew Goodrick-Werner says:

March 8, 2011 at 8:08 am

I’ve updated my version of the script to take into account dock position and menu bar height — I also made sure to include your Terminal workaround, Tim. Enjoy! 🙂

tell application “Finder”
set screenSize to bounds of window of desktop
set screenWidth to item 3 of screenSize
set screenHeight to item 4 of screenSize
end tell

tell application “System Events”
tell dock preferences
if screen edge is bottom then
tell application “System Events” to tell process “Dock”
set dockSize to size in list 1
set dockHeight to item 2 of dockSize
set screenHeight to (screenHeight – dockHeight)
end tell
else if screen edge is left then
tell application “System Events” to tell process “Dock”
set dockSize to size in list 1
set dockHeight to item 1 of dockSize
set screenWidth to (screenWidth + dockHeight)
end tell
else
tell application “System Events” to tell process “Dock”
set dockSize to size in list 1
set dockHeight to item 1 of dockSize
set screenWidth to (screenWidth – dockHeight)
end tell
end if
end tell

set screenHeight to (screenHeight + 22)
set myFrontMost to name of first item of ¬
(processes whose frontmost is true)
end tell

try
tell application myFrontMost
set windowSize to bounds of window 1
set windowXl to item 1 of windowSize
set windowYt to item 2 of windowSize
set windowXr to item 3 of windowSize
set windowYb to item 4 of windowSize

set windowWidth to windowXr – windowXl
set windowHeight to windowYb – windowYt

if myFrontMost is “Terminal” then
set bounds of window 1 to {¬
round ((screenWidth – windowWidth) / 2) rounding as taught in school, ¬
round ((screenHeight – windowHeight) / 2) rounding as taught in school, ¬
round ((screenWidth + windowWidth) / 2) rounding as taught in school, ¬
round ((screenHeight + windowHeight) / 2) rounding as taught in school}
else
set bounds of window 1 to {¬
round ((screenWidth – windowWidth) / 2) rounding as taught in school, ¬
round ((screenHeight – windowHeight) / 2) rounding as taught in school, ¬
round ((screenWidth + windowWidth) / 2) rounding as taught in school, ¬
round ((screenHeight + windowHeight) / 2) rounding as taught in school}
end if

set the result to bounds of window 1

end tell
end try

Reply
Lri says:

March 10, 2011 at 1:01 am

I posted yet another version at the apple.stackexchange thread.

Reply
Claudia Putnam says:

September 19, 2014 at 6:42 am

I just want it to center horizontally. I don’t care if it goes to the top of the screen as long as I can still get to the menu bar. But when I downloaded I got a Failed-insufficient permissions message. ?

Reply
1. Tim Moore says:
  
  September 23, 2014 at 8:08 pm
  
  Claudia, can you be more specific about what went wrong? Was it downloading the file that gave you that message, or after you downloaded it?
  
  Reply
  1. Claudia Putnam says:
    
    September 24, 2014 at 12:33 am
    
    There was a message on the download file itself. You know how mac puts downloads at the bottom of your screen? It said: Name of file, then Download: Failed, insufficient permissions. I couldn’t get it to open, either.
    
    Reply
    1. Tim Moore says:
      
      September 24, 2014 at 10:29 am
      
      I’m not sure why, Claudia. It works when I try it. Have you tried again? If it doesn’t work, you can copy and paste the code into Script Editor, or better yet, try the app I now use instead of this script: http://spectacleapp.com/
      
      Reply
      1. Claudia Putnam says:
        
        September 24, 2014 at 10:48 am
        
        Thanks. That’s a great app. I still have to move it to the top of the screen, but it’s better than nothing. 🙂 (The top half option is not what I want… )
Claudia Putnam says:

September 24, 2014 at 10:50 am

(I’m not a very good Mac user. Having used Windows for about as long as there’s been a Microsoft, I haven’t been able to adjust well after nearly 3 years on my Mac. There are probably a million things you can do that I haven’t been able to find or figure out.)

Reply
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Woosang Kwon says:

October 8, 2017 at 10:52 pm

I’ve been searching on the internet because I really wanted to put the windows in the centre, and your tip (about the app) was very very helpful! Thank you for sharing!

Reply
Colin says:

August 12, 2019 at 6:31 am

I recently stumbled upon WindowSizer which does this (but it’s a paid app): https://mattrajca.com/windowsizer/

Reply
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27 Replies to “Centering Windows in Mac OS X with AppleScript”

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