SD card compatibility for Canon EOS 6D Mark II explained—SDXC, UHS-I, 256GB support, and real-world performance guidance.
Practical guidance for photographers
When a photographer asks whether a particular SD card will “work” in a camera, the question usually conceals several related concerns: physical compatibility (will the card fit?), logical compatibility (does the camera’s firmware support the card type and capacity?), and performance compatibility (can the card sustain the write/read speeds your workflow or shooting mode requires?). For owners of the Canon EOS 6D Mark II these concerns are straightforward to resolve — but only if they are understood in concrete, practical terms.
This article unpacks what the 6D Mark II accepts, how card types and speed classes affect real-world shooting, and what you should do if you want to use a large-capacity card such as a 256 GB Lexar card with this body. The aim is practical clarity — no marketing spin, no techno-fear — so you can make confident choices in the field.
What the 6D Mark II officially supports
Canon’s published specifications and the camera’s user manual are the primary authorities here: the EOS 6D Mark II records to SD, SDHC and SDXC media, and supports the UHS-I interface (Canon, 2017). In plain language, that means the camera will accept current SD card standards up to SDXC capacity (the SDXC standard itself allows capacities up to 2 TB), and it speaks the UHS-I protocol — but not UHS-II or UHS-III at the faster bus standards those cards can operate on (Canon, 2017; Canon regional specs page). In practice, UHS-II cards will function in a UHS-I device, they’ll simply operate at UHS-I speeds.
Because the camera supports SDXC, a modern 256 GB SDXC card is, in principle, compatible; the theoretical capacity limit is well beyond 256 GB. That explains why photographers successfully use 256 GB and higher capacity SDXC cards in the 6D Mark II (Canon Community threads and independent reviews corroborate the point) (Canon Community, n.d.; Imaging-Resource, 2017).
Card types, classes and what they mean for shooting
Understanding the labels on SD cards will remove most confusion:
- SD / SDHC / SDXC — these refer to the card family and its capacity range. SDXC is the family that includes 64 GB and above. The 6D Mark II supports SDXC.
- UHS (Ultra High Speed) bus — UHS-I / UHS-II — these indicate how data is transferred on the bus. The 6D Mark II supports UHS-I; UHS-II cards are backwards-compatible but will fall back to UHS-I speeds in this body.
- Speed classes (Class 10, U1, U3, V30, etc.) — these are minimum sustained write performance markers used especially for video workflows. For still shooting the most important factor is write speed during bursts and buffer clearing.
For still photographers — particularly those shooting birds-in-flight or any sustained continuous shots — write speed and sustained throughput matter. The 6D Mark II has a single card slot and an internal buffer; if write speed is slow relative to your burst data, the buffer fills and shooting cadence slows as the camera writes to the card. Practically, that means a modern, high-quality SDXC card with solid sustained write rates (cards labelled UHS-I U3 or V30 and above) will give the best real-world performance on the 6D Mark II, even though the camera does not use the higher UHS-II bus (Imaging-Resource, 2017).
Using 256 GB and larger cards — capacity vs. compatibility
Capacity itself is not typically the compatibility constraint. Because the 6D Mark II is SDXC-capable, a 256 GB SDXC card will be recognized and can be formatted and used by the camera (Canon, 2017). Reports from users and retailers verify this: pro-tier 256 GB SDXC cards (SanDisk, Lexar, Angelbird, etc.) are commonly sold as “compatible with Canon EOS 6D Mark II” and routinely used by photographers with that body (B&H; retailer listings; Canon community experiences) (B&H Photo, n.d.; Canon Community, n.d.).
A couple of practical caveats are worth noting:
- Format cards in-camera. If you insert a new card that was previously formatted by a computer or another device, format it in the camera before shooting. In-camera formatting writes the camera’s directory structure and reduces the chance of filesystem issues (Canon manual, 2017).
- Use reputable brands. Counterfeit or low-quality flash media create more headaches than compatibility questions. A genuine Lexar, SanDisk, Angelbird or similarly reputable SDXC card reduces the risk of corrupted files or performance variance. Most camera makers and memory vendors recommend buying from official channels.
- Check card firmware updates for extreme edge cases. Rarely, very new cards that push novel controller designs or obscure optimizations might reveal quirks with older camera firmware. In such cases check Canon support notes or vendor compatibility lists; however, this is an exception rather than the rule (Lexar compatibility guide; Canon support pages) (Lexar, 2024; Canon, 2017).
Short answer: yes — provided it is an SDXC card and not a mislabeled counterfeit, the 6D Mark II will accept a 256 GB Lexar SDXC card and operate normally. Numerous photographers report successful use of 256 GB SDXC cards in this camera; Canon’s own specifications list SDXC as compatible (Canon, 2017; Canon regional specs). Because the 6D Mark II supports only the UHS-I bus, UHS-II Lexar cards will function but operate at UHS-I speeds. If your Lexar card is a UHS-I, rated for sustained writes at U3/V30 levels (or equivalent), it will be a robust choice for bursts and higher-resolution image files.
Performance considerations in the field
Two points determine shooting experience more than raw capacity:
- Sustained write speed: For long bursts (wildlife action sequences, high frame-rate continuous shooting) choose cards with consistently high sustained write speeds. Cards marketed as “U3” or “V30/V60” give reasonable assurances of sustained performance. Even though UHS-II cards may advertise higher peaks, the 6D Mark II will fall back to UHS-I speeds. So a high-quality UHS-I U3/V30 card often gives the best balance of performance and cost for this body.
- Card reader speed on your workstation: Large cards and many files are meaningful only if your workflow offloads efficiently. Use a quality USB 3.0 reader to move files swiftly into your editing system.
Also, remember practical field habits: swap cards between sessions rather than filling a single card to capacity without backup; when traveling consider using multiple 128 GB or 64 GB cards for redundancy; back up files at the day’s end. Capacity is convenient but not a replacement for sound data-management discipline.
Troubleshooting common issues
If a card does not function in the 6D Mark II:
- Format it in-camera. This resolves most “not recognized” or odd behavior instances.
- Try another card. If a different SDXC card works, the first card may be faulty or counterfeit.
- Try the card in a reader. If your computer cannot read the card, the card itself may be defective.
- Check firmware. Ensure your camera firmware is up to date; Canon occasionally issues firmware to improve system stability and card handling.
- Avoid cheap, unbranded cards. Price-conscious choices can introduce file corruption risk.
For the majority of 6D Mark II users — including wildlife and birds-in-flight shooters who depend on consistency rather than experimental peak speeds — choose a reputable SDXC card with UHS-I interface and U3/V30 (or higher) sustained write rating. A Lexar Professional 256 GB SDXC (or a SanDisk Extreme Pro 256 GB SDXC) fits this recommendation: it offers high capacity, reputable manufacturing, and solid sustained write performance. Format it in-camera, use a reliable card reader for offloading, and adopt a day-end backup routine.
Conclusion
Compatibility questions often have deceptively simple answers. The Canon EOS 6D Mark II supports SD, SDHC and SDXC cards and is UHS-I compatible; therefore modern 256 GB SDXC cards are within the camera’s official compatibility range and will function when genuine and formatted appropriately (Canon, 2017). Speed choices matter more than capacity for shooting experience: choose reputable SDXC cards rated for sustained writes and accept that UHS-II peak performance will be constrained by the camera’s UHS-I interface. With sound card selection and good data-management discipline, the 6D Mark II remains a reliable workhorse — even with large modern SDXC cards." (Source: ChatGPT 5.2 : Moderation: Vernon Chalmers Photography)
References
B&H Photo Video. (n.d.). Memory cards compatible with Canon EOS 6D Mark II. B&H. Retrieved from https://www.bhphotovideo.com
Canon Inc. (2017). EOS 6D Mark II instruction manual (Digital manual). Retrieved from https://global.canon/en/support/8203585600 (see “Recording media” / “Compatible cards”)
Canon Inc. (n.d.). Canon EOS 6D Mark II specifications and features. Canon regional product pages. Retrieved from https://www.canon.co.za/cameras/eos-6d-mark-ii/specifications/ and https://asia.canon/en/support/6200470100
Imaging Resource. (2017). Canon EOS 6D Mark II review. Imaging-Resource. Retrieved from https://www.imaging-resource.com
Lexar. (2024). SD compatibility guide (Technical document). Lexar. Retrieved from https://www-oss.lexar.com/lexar/resource/files/2024-12-20/SD_compatibility_GL_2024Q4.pdf
Canon Community. (n.d.). User forum threads on card size and compatibility. Canon Community Support Forums. Retrieved from https://community.usa.canon.com
