DMG background helper
Set the window and the two icons, add your picture if you have one, and copy the command. The picture stays on this page and is never uploaded.
Try a size:
What it does
Most Mac apps sold outside the Mac App Store come as a DMG: a disk image that opens into a small Finder window with the app on one side and a link to Applications on the other, over a background picture that says "drag here". Getting that window right takes a few rounds of guessing numbers. This tool draws the window at the size you set, puts the two icons where you say, and lets you drag them. It checks that nothing sticks out or overlaps, checks your picture against the window, and writes the create-dmg command that builds it.
The sizes that matter
| What | How it is counted |
|---|---|
| Window size | In points, the whole Finder window, title bar included |
| Background picture | The same number of pixels as the window has points, such as 660 x 400 for a 660 x 400 window |
| Retina copy | Twice that, such as 1320 x 800, named with @2x |
| Icon size | Up to 128 in create-dmg |
| Text size | 10 to 16 in create-dmg |
| Icon position | The middle of the icon, in points from the top left corner of the window |
Commands to run
brew install create-dmg tiffutil -cathidpicheck background.png background@2x.png -out background.tiff
The first installs create-dmg. The second, built into macOS, joins your normal and Retina pictures into one TIFF, so Finder can pick the sharp one on a Retina screen. Its manual says it warns you if the two sizes don't match. The tool writes the full create-dmg command for you as you go. After building, sign and notarize the DMG like the app inside it.
What each result means
| Mark | What it means |
|---|---|
| Fix | The window will look broken: an icon sticks out or covers the other, or the picture is the wrong size. |
| Look | It will build, but something is tight, like an icon close to the edge or a very big window. |
| OK | It fits. |
| Note | Good to know, such as what to name the Retina copy. |
Sources: create-dmg on GitHub, its README and its Finder script, and the tiffutil manual page in macOS (man tiffutil), all read November 12, 2026.
How it works
It is plain arithmetic running on this page. Your picture is read by your browser to get its size and draw it, and it is never uploaded. The 24 point margin and the 1000 by 700 window warning are our own rules of thumb, not Apple's. The name under each icon is counted as one line, so a long app name that wraps needs a little more room. It can't see Finder itself, so open the finished DMG once on your own Mac before you ship it.
Questions
What size should a DMG background image be?
The same size in pixels as the window is in points, for example 660 by 400 for a 660 by 400 window, plus a copy at twice the size, 1320 by 800, for Retina screens.
How do I make a Retina DMG background?
Save both sizes as background.png and background@2x.png, then run tiffutil -cathidpicheck background.png background@2x.png -out background.tiff and use the TIFF as the background.
Where does an icon position point to?
To the middle of the icon, counted in points from the top left corner of the window. Finder puts the name underneath, so leave room below it.
How big can the icons in a DMG be?
create-dmg takes an icon size of up to 128 points and a text size from 10 to 16.
Is my picture uploaded?
No. Your browser reads it on this page to get its size and show it. Nothing is sent or stored.