Best SD Card for Your CPAP (2026 Guide)

The SD card in your CPAP machine is a small thing that trips up a lot of people. Wrong size, wrong format, wrong reader on their laptop, and suddenly they can't get their data. This guide covers everything you need to know: what type of card your machine uses, what size to buy, whether you need a ResMed-branded card (you don't), and how to actually read it on a computer.

What Card Your Machine Uses

ResMed machines use a standard, full-size SD card. That's the one that's 32mm x 24mm, the same size that was in digital cameras before everything went mirrorless. Not micro SD, not mini SD. The full-size card.

This applies across the entire current ResMed lineup:

• AirSense 11 AutoSet
• AirSense 10 AutoSet
• AirCurve 10 (all variants)
• AirCurve 11 (all variants)

The slot is on the side of the machine, usually behind a small door. On the AirSense 11 it's on the left side (behind the water chamber) when you're facing the front. On the AirSense 10 it's on the right side behind a small flip-open door.

The card that ships with the machine is either 2GB (AirSense 10) or 4GB (AirSense 11). These are adequate but small by today's standards. You can replace them with anything up to 32GB and the machine will work fine.

What Size to Get

Two constraints matter here: capacity and format.

Maximum size: 32GB. Cards larger than 32GB use the exFAT filesystem by default, and ResMed machines cannot read exFAT. A 64GB card will not work. Stay at 32GB or under.

Required format: FAT32. This is the filesystem format, separate from the card's storage capacity. Cards 32GB and under ship from the factory pre-formatted as FAT32, so most people never need to think about this. More on formatting below.

The practical sweet spot: 8GB. At $5 – $8 (as of April 2026), an 8GB card gives you years of data storage and leaves room for the machine's folder structure to grow. Here's why that's more than enough:

• AirSense 11: writes approximately 2 – 5 MB of data per night
• AirSense 10: writes approximately 5 – 15 MB of data per night (stores more detailed waveform data)

A 4GB card holds roughly 1 – 3 years of nightly data depending on your machine model and therapy settings. An 8GB card doubles that. A 32GB card is essentially unlimited for practical purposes. Any of these are fine choices.

There is no benefit to going above 32GB, and cards in that range cost more anyway.

Do You Need a ResMed-Branded Card?

No. ResMed sells SD cards as accessories, typically at $15 – $25 for a 4GB card (as of April 2026). That's a significant markup over what the card actually costs. The ResMed-branded cards are standard SanDisk or Kingston SD cards repackaged with ResMed branding.

A generic 32GB SD card from SanDisk, Kingston, or Samsung costs $5 – $8 at the same retailers. It's the same hardware. The machine doesn't check who made the card.

One thing worth knowing: you don't need to create any folders manually before inserting a new card. The machine creates its own directory structure (the DATALOG folder and related directories) the first time it runs with a new card. Just format it FAT32, insert it, and use the machine as normal. After your first night of therapy, the folders will be there.

How to Format Your Card

Most cards 32GB and under are already formatted FAT32 when you buy them. You only need to format a card yourself if:

• You're reusing an old card that was formatted differently
• The machine is throwing errors reading the card
• You want to clear old data and start fresh

On Windows: Insert the card, open File Explorer, right-click the drive, choose Format. In the File System dropdown, select FAT32. Make sure "Quick Format" is checked and click Start. That's it.

On Mac: Open Disk Utility (Applications > Utilities > Disk Utility). Select the SD card in the left sidebar. Click Erase. In the Format dropdown, choose MS-DOS (FAT). Give it a name (anything works) and click Erase.

One rule: don't manually create folders. The machine expects to create its own folder structure. If you create a DATALOG folder yourself, you may cause a conflict. Start with an empty, formatted card.

What Does NOT Work

A few things people try that don't work:

Cards larger than 32GB. The exFAT format these cards use is not compatible with ResMed firmware. A 64GB or 128GB card will not be recognized by the machine.

Micro SD with an adapter. Physically, a micro SD card with a full-size adapter can fit in the slot. In practice, the fit is loose and the card can shift during the night or when you move the machine. This is a common cause of corrupt data or missing nights. Use a real full-size SD card.

WiFi SD cards. Cards like Eye-Fi or Toshiba FlashAir have wireless chips built in and appear to be regular SD cards. They are not compatible with ResMed firmware. The machine either won't recognize them or will write corrupted data.

How to Read Your Card on a Computer

To import your CPAP data into CPAP Clarity (or any analysis software), you need to connect the card to your computer. A few options:

Built-in SD card slot. Many laptops, particularly Windows laptops and older MacBooks, have a full-size SD card slot built in. If yours does, just insert the card directly.

USB-C SD card reader. Most modern MacBooks and Windows laptops use USB-C exclusively. A small USB-C SD card reader (opens in new tab) ($8 – $15) is the cleanest solution. Look for one that supports SD 3.0 or UHS-I speeds, though any reader will work fine for the data volumes involved.

USB-A SD card reader. If your computer has USB-A ports, a USB-A SD card reader (opens in new tab) works the same way and tends to be a bit cheaper.

Android phone via USB OTG. Android phones with USB OTG support can connect to a card reader and access the SD card. Combined with a mobile browser, you can import your data directly from your phone. CPAP Clarity's folder import works in Chrome on Android.

iPhone or iPad: Current iPhones (iPhone 15 and later) use USB-C, so a USB-C SD card reader (opens in new tab) will connect directly. Older iPhones with Lightning ports need a Lightning SD card reader (opens in new tab). Either way, you can view files in the Files app. However, Safari on iOS does not support the folder selection that CPAP data import requires. This is an Apple platform limitation, not a CPAP Clarity limitation. iPhone and iPad users currently need a computer for full SD card import.

Prices and availability as of April 2026.

Our Picks

These are straightforward recommendations with no surprises.

SD Card: A SanDisk or Kingston 8 – 32GB standard SD card (opens in new tab) in the $5 – $8 range covers every CPAP use case. Stick with name-brand cards from SanDisk, Kingston, or Samsung. Off-brand cards occasionally have reliability issues.

USB-C Reader: Any USB-C SD card reader (opens in new tab) that supports full-size SD cards from a name you recognize. Anker and uni make solid ones in the $10 – $15 range.

USB-A Reader: Same story for USB-A (opens in new tab). Often a couple dollars cheaper than the USB-C equivalent.

You don't need anything faster or more expensive than these for CPAP data. The files are small and any reader will transfer them in seconds.

Prices and availability as of April 2026.

Once You Have the Card

The workflow is simple. Insert the card into your machine before going to sleep. Use your machine as normal. In the morning, remove the card and insert it into your computer using whichever reader applies to you.

Open CPAP Clarity and select the whole SD card folder when prompted. The import reads the entire DATALOG directory and all session files automatically. You don't need to pick individual files.

For a full walkthrough of the import process, see the CPAP SD card data guide. If you're new to CPAP Clarity, How to Use CPAP Clarity is the place to start. Once your data is in, How to Read Your CPAP Data explains what all the numbers mean.

Common Questions

Can I use the same card in OSCAR and CPAP Clarity?

Yes. Both tools read the same files from the same SD card. You can import into CPAP Clarity, then plug the same card into OSCAR (or vice versa) without any issues. The files are not modified during import. If you're curious how CPAP Clarity compares to OSCAR, see our OSCAR alternative guide.

Does removing the card affect my therapy?

No. The SD card records data but plays no role in delivering therapy. Removing it (while the machine is off) does not change pressure, humidification, or any other setting. The machine will simply not record data on nights when the card isn't present.

How often should I check my data?

That depends on where you are in your therapy. In the first few weeks, checking weekly gives you a sense of how your body is adjusting. Once therapy is stable, monthly is plenty for most people. If you're troubleshooting a problem (high leak rate, poor sleep quality), daily check-ins are worthwhile until the issue is resolved.

What do I do if the card is full?

Two options. First, you can reformat the card (FAT32, as described above) to wipe it and start fresh. Second, you can replace it with a larger card, up to 32GB. If you want to keep your historical data, copy the DATALOG folder to your computer before reformatting or swapping cards.

Can I leave the card in the machine all the time?

Yes, and most people do. The card is only accessed when the machine is writing data at the end of a session. Leaving it in is fine. Just remember to remove it when you want to import your data.