Guide
Using your Android phone's SD card on a Mac
Most phone cards open on a Mac like any memory card. One kind never will, and there is a way to reach both without taking the card out of the phone.
There are two ways to get at a phone's microSD card from a Mac. Take it out and put it in a card reader, or leave it in the phone and reach it over the USB cable. A card set up as portable storage, which is how most phones set one up, works both ways, and macOS reads and writes it with nothing to install.
The exception is a card the phone adopted as internal storage. That one is encrypted for the phone that formatted it, and no Mac can read it in a reader. Its files are still reachable, but only through the phone. Here is how to tell which you have, and how to work with each.
In a card reader
The 14-inch and 16-inch MacBook Pro from 2021 onwards and the Mac Studio have a full-size SDXC slot, so a microSD card needs a plain adapter. Other Macs need a USB card reader.
A portable card is formatted in one of two file systems, and macOS reads and writes both:
- FAT32, on cards up to 32 GB (SDHC). No single file can be larger than 4 GB, so a long video will refuse to copy onto it.
- exFAT, on cards of 64 GB and more (SDXC). No practical file size limit.
The card mounts in Finder like a USB stick. Copy what you need, then eject it in Finder before you pull it out, as you would any drive.
There is one side effect. When the Mac copies files onto a FAT32 or exFAT card, it writes a small hidden twin next to each one, named with ._ in front. Back in the phone, music players and galleries can trip over them. The ._ files on your Android phone explains what they are and how to stop them.
The card a Mac cannot read
Since Android 6, a phone can adopt a card as internal storage. It formats the card with a Linux file system and encrypts it with a key that stays on that phone, so that it "can't be mounted elsewhere", in the words of Android's own documentation. The card then adds to the phone's storage and can hold apps, but it belongs to that phone alone.
Put an adopted card in a Mac and macOS will say the disk is not readable by this computer, and offer to initialise it. Do not. Initialising erases the card. No Mac software can read it, because the key is in the phone, not on the card.
To get your files off an adopted card, go through the phone, with the card still in it: over the cable, the files appear as part of the phone's own storage. Once you have a copy, you can turn the card back into portable storage on the phone. Google's steps are Settings > Storage > SD card > menu > Format > Format card, and that erases it too.
Samsung says it no longer supports adoptable storage on Galaxy devices, so a card from a recent Galaxy is portable. On a phone that does offer the choice, a new card asks when you first put it in: Format for portable storage, or Format another way to adopt it.
| How the card is set up | In a Mac card reader | Through the phone, with an MTP app | Through the phone, with SideMount |
|---|---|---|---|
| Portable, FAT32 (up to 32 GB) | Reads and writes, files up to 4 GB | Its own storage, files up to 4 GB | A folder named SD Card, files up to 4 GB |
| Portable, exFAT (64 GB and more) | Reads and writes | Its own storage | A folder named SD Card |
| Adopted as internal storage | Unreadable, macOS offers to erase it | Part of the phone's storage | Part of the phone's storage |
Leaving the card in the phone
You do not have to take the card out at all. Over the USB cable, the phone serves the card's files itself, and that has three advantages: there is no tray to open and no adapter to lose, the phone keeps working while you copy, and an adopted card is reachable too.
MTP apps, such as OpenMTP or the old Android File Transfer, list the card as a second storage beside the internal one, in their own window. Choose the phone's File transfer mode in its USB notification first.
SideMount mounts the phone as a volume in Finder instead. Internal storage is the volume itself, and each SD card is a folder at the top of it, named SD Card. You drag files in and out as you would on any drive, and any Mac app can open them in place: a video in VLC, a RAW file in Lightroom, a folder with rsync. It never leaves ._ or .DS_Store files on the phone, card included, because Finder's extra data is kept on the Mac while the phone is mounted.
The cable sets the pace. A USB 2 phone or cable holds any method to about 20 to 40 MB/s, while over USB 3 SideMount moves large files at well over 100 MB/s. The card itself can be the slowest part: a card marked V30 or U3 promises at least 30 MB/s of sustained writing, and many cheaper cards promise less. How to check a USB-C cable on a Mac shows how to read the speed your phone is linked at.
Moving files between internal storage and the card
On the phone
In Files by Google, find the file, tap More > Move to, choose SD card, pick a folder and tap Move here. For several files, select them first. Samsung's My Files works the same way: select the files, tap Move, go back to the home screen, open SD card and tap Move here.
To save new photos to the card on a Galaxy, open the Camera's settings and set Storage location to SD card. The option only appears while a card is inserted. Photos you have already taken stay where they are, so move those with My Files.
On the Mac
With the phone mounted in Finder this way, drag a file from a folder of internal storage into the SD Card folder. The phone does the copy itself, so the data does not travel through the Mac, but Finder shows no progress bar while it happens. Give a large folder time to finish before you eject.
The first connection needs USB debugging turned on once and the Mac allowed on the phone. The setup guide covers it, and every way to move files between Android and a Mac compares the other routes.
Questions
Why does my Mac say my phone's SD card is not readable?
Most often because the phone adopted the card as internal storage, which encrypts it for that phone alone. A damaged card gives the same message. Do not let macOS initialise it, because that erases it. Put the card back in the phone and copy the files over the USB cable instead.
Can I copy a file bigger than 4 GB to my phone's SD card?
Only if the card is formatted as exFAT, as cards of 64 GB and more usually are. A FAT32 card, the usual format up to 32 GB, cannot hold any single file over 4 GB, whether you copy in a card reader or through the phone.
Will my Mac leave ._ files on the SD card?
In a card reader, yes: macOS writes a hidden ._ file beside each file it copies onto a FAT32 or exFAT card. Through an MTP app, no, and SideMount refuses them on the phone. Either way, they are harmless and safe to delete.
Do Samsung phones support adoptable storage?
No. Samsung left it out of its flagships from the Galaxy S7 onwards, and its support pages say it no longer supports adoptable storage on Galaxy devices. So a card from a recent Galaxy is portable storage and opens in a Mac card reader. Some other Android phones with a card slot offer both choices.
