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06 Numbers and Powers

DMG to ISO: How to Convert and What You Need

Card No. 06·15848 · Updated · Standard formula, shown below

Average pace 5.00 min/km
Average speed
12.00 km/h
Result
Finish time
50 min
You entered
Distance
10 km
You entered
You enter
Finish time, Distance
You get
Average pace, Average speed
Rounding
2 dp

Yes, you can easily convert a DMG image to an ISO file, and the process is straightforward on macOS using the built-in Disk Utility or the hdiutil command-line tool. You can also do it on Windows or Linux with third-party tools, though the steps differ. This article explains the methods, the differences between the formats, and the common pitfalls to avoid.

What Is a DMG File?

DMG (Apple Disk Image) is a file format used by macOS to distribute software and create mountable disk volumes. It can contain a filesystem (like HFS+, APFS, or FAT) and may be compressed or encrypted. DMG files are native to macOS and are not natively recognized by Windows or most Linux distributions. They are often used for app installers, backups, and sharing folders.

What Is an ISO File?

ISO (International Organization for Standardization) is a widely supported disk image format based on the ISO 9660 standard. It contains an exact sector-by-sector copy of an optical disc (CD, DVD, Blu-ray). ISO files are universally recognized by operating systems, virtualization software, and disc-burning tools. They are the de facto standard for distributing operating system images and large software packages.

Why Convert DMG to ISO?

There are several common reasons to convert a DMG to ISO:

  • Cross-platform compatibility: ISO files can be mounted on Windows, macOS, and Linux without extra software, while DMG files require third-party tools on non-Mac systems.
  • Virtualization: Programs like VirtualBox, VMware, and QEMU often accept ISO images more readily than DMG files for installing guest operating systems.
  • Burning to disc: If you need to create a bootable CD/DVD, ISO is the standard format that most burning software expects.
  • Archival: ISO is a simpler, more universal format for long-term storage, especially if the DMG is not encrypted or compressed.

How to Convert DMG to ISO on macOS

macOS provides two built-in methods: Disk Utility (graphical) and the hdiutil command (terminal). Both produce an ISO-compatible file, but note that the resulting ISO may not be bootable on all systems if the original DMG contained a Mac-specific filesystem like HFS+ or APFS. For best compatibility, the DMG should contain a UDF or ISO 9660 filesystem.

Method 1: Using Disk Utility

  1. Open Disk Utility (Applications > Utilities).
  2. In the menu bar, select File > Open Image and choose your DMG file. It will appear in the sidebar.
  3. Select the mounted volume in the sidebar.
  4. Go to File > Convert Image (or right-click and choose Convert).
  5. In the dialog, choose a destination and set Image Format to DVD/CD master. This creates a CDR file, which is essentially an ISO with a different extension.
  6. Click Convert. A .cdr file is created.
  7. Rename the .cdr file to .iso (e.g., image.cdr to image.iso). macOS will prompt you to confirm the extension change.

Method 2: Using the Terminal (hdiutil)

  1. Open Terminal (Applications > Utilities).
  2. Run the following command, replacing source.dmg with your file name and output.iso with the desired output name:
hdiutil convert /path/to/source.dmg -format UDTO -o /path/to/output.iso

This creates output.iso.cdr. Rename it to output.iso:

mv /path/to/output.iso.cdr /path/to/output.iso

The -format UDTO option stands for “DVD/CD master,” which produces a raw ISO-compatible image.

How to Convert DMG to ISO on Windows and Linux

On Windows, you need third-party software because the OS does not natively read DMG files. Popular options include:

  • 7-Zip: Can extract the contents of a DMG, but not directly convert to ISO. You would extract and then create an ISO from the extracted files using a tool like ImgBurn or the Windows 10/11 built-in ISO creation (via right-click > Burn to disc).
  • DMG2IMG: A small command-line tool specifically designed to convert DMG to IMG or ISO. It works on Windows and Linux.
  • PowerISO: A commercial tool that can open and convert DMG files to ISO.

On Linux, the dmg2img package is available in most repositories. Install it with your package manager, then run:

dmg2img source.dmg output.iso

This tool handles the DMG structure and produces a raw image that can be written to disc or mounted.

Common Problems and Misconceptions

One frequent issue is that the converted ISO doesn’t boot on non-Mac hardware. This happens because many DMG files contain HFS+ or APFS filesystems, which Windows and most PC BIOS/UEFI systems cannot read. The conversion only changes the container format, not the internal filesystem. To create a bootable ISO for Windows or Linux, the DMG must already contain a compatible filesystem (like UDF or ISO 9660). If it doesn’t, you’ll need to extract the contents and rebuild an ISO with the appropriate filesystem.

Another misconception is that DMG files are always compressed. While many are, some are raw images. The conversion process does not recompress; it simply strips the DMG container. The resulting ISO may be larger than the original DMG if the DMG was compressed.

Encrypted DMG files must be decrypted before conversion. Disk Utility will prompt for the password, and hdiutil can use the -passphrase option or will ask interactively. The output ISO will not be encrypted.

Alternatives to Conversion

If you only need to access the contents of a DMG on Windows, you can use 7-Zip to extract files without converting. On macOS, you can mount the DMG directly. If you need to share files with Windows users, consider using a ZIP archive instead of converting to ISO, as ZIP is universally supported and preserves permissions better for some use cases.

Frequently Asked Questions

Can I convert a DMG to ISO without losing data?

Yes, conversion is lossless in terms of file content. The files inside the DMG are copied as-is into the ISO container. However, if the DMG is compressed, the ISO will be larger. Also, if the DMG uses a Mac-only filesystem, the ISO may not be readable on other OSes, but the data is still intact.

Is it legal to convert DMG to ISO?

Yes, conversion is a format change, not a copyright violation, as long as you have the right to use the software or content. For commercial software, check the license agreement; some prohibit redistribution or modification, but personal conversion for backup is generally acceptable.

Why does my converted ISO not boot on Windows?

As mentioned, the ISO inherits the filesystem of the original DMG. If it’s HFS+ or APFS, Windows cannot boot it. You need to create a new ISO with a Windows-compatible filesystem (like UDF or ISO 9660) from the extracted contents. Tools like ImgBurn or Rufus can do this.

Can I convert a DMG to ISO on an iPhone or iPad?

No, iOS/iPadOS does not provide a built-in way to convert DMG files. You would need to transfer the DMG to a computer and use the methods above.

What is the difference between DMG and ISO in terms of size?

DMG files can be compressed, so they are often smaller than the resulting ISO. ISO files are typically uncompressed raw images, so they take up more space. For example, a 2 GB compressed DMG might expand to a 4 GB ISO.

Do I need to install extra software on macOS to convert?

No, Disk Utility and the hdiutil command are built-in. No third-party software is required.

Related

Formula used
in t | Finish time | min | 50 | 0
in d | Distance | km | 10 | 0 | 100000
out pace | Average pace | min/km | t / d | 2
out speed | Average speed | km/h | d / (t / 60) | 2

Each line is one input (in, sel, list) or one result (out: label, unit, formula, decimals). How the calculators work

Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.

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