SD Card Speed Classes Explained
Demystifying U1, U3, V30, V60 & What You Actually Need
Don't risk dropped frames or slow performance. This guide simplifies SD card speed ratings so you can confidently choose the right card for 4K video, RAW photography, and gaming without overspending.
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Quick Answer: What Speed Class Do You Need?
No time for details? Find your use case below.
For 4K Video
V30 or U3 is essential. This guarantees a 30 MB/s minimum write speed, preventing dropped frames. For high-bitrate 4K (120fps+), get a V60 card.
For Photography
U3 is best for RAW burst shooting. U1 is fine for single shots. The faster rating helps clear the camera's buffer quicker, letting you shoot more consecutive photos.
For Gaming & Apps
Look for the A2 rating. Application Performance Class (A1/A2) is crucial for fast app loading on devices like the Steam Deck or Nintendo Switch. V30 is also a good indicator.
What Do SD Card Speed Ratings Mean?
An SD card's speed class is a promise: it guarantees a **minimum sustained write speed**. This is crucial for video recording, where a dip in speed can cause your camera to stop recording or drop frames, ruining a shot.
Think of it like a highway's speed limit. A "V30" card promises to never drop below 30 MB/s. This is different from the "max speed" (e.g., "up to 170 MB/s") printed on the front, which is only achievable in short bursts under ideal conditions. For video, the minimum speed is what matters. This guide breaks down the different rating systems (U-Class, V-Class, and A-Class).
How to Decode the Symbols on Your SD Card
The front of an SD card is covered in symbols. Here’s what the most important ones mean:
- Card Type: SDHC (up to 32GB) or SDXC (32GB and larger).
- Storage Capacity: The card's total storage in Gigabytes (GB) or Terabytes (TB).
- Max Read Speed: The theoretical peak speed, usually for reading data. Not a guaranteed speed.
- Video Speed Class (V-Class): The most important rating for video. V30 = 30 MB/s minimum.
- UHS Speed Class (U-Class): An older but still common video speed rating. U3 = 30 MB/s minimum.
- Bus Interface: UHS-I or UHS-II. UHS-II cards have a second row of pins for much faster speeds.
- Application Performance Class (A-Class): Important for phones and gaming devices. A2 is faster than A1.
1 Video Speed Class (V-Class): The Modern Standard for Video
The V-Class rating is the clearest indicator of a card's capability for video. It's the most recent standard, designed for 4K, 8K, and high-frame-rate recording.
V30
30 MB/s
The Sweet Spot: Essential for standard 4K video (24/30fps) on most mirrorless cameras, drones, and action cams.
V60
60 MB/s
Pro & High-Frame-Rate: Needed for high-bitrate 4K (60/120fps) or entry-level 8K recording. Also great for RAW burst photography.
V90
90 MB/s
Cinema & 8K: Required for professional cinema cameras shooting uncompressed 8K RAW video. Overkill for most users.
V10 / V6
10 / 6 MB/s
Legacy: Sufficient for 1080p HD video. Not recommended for any 4K capable device.
Key Takeaway: For any modern camera that shoots 4K, **V30 is the minimum you should consider.**
2 UHS Speed Class (U-Class): The Common All-Rounder
Before V-Class, the U-Class was the primary indicator for 4K video. It's still widely used and relevant.
U1
10 MB/s
Sufficient for 1080p video, single-shot photography, and general use. **Not recommended for 4K video.**
U3
30 MB/s
Functionally identical to V30. It guarantees the 30 MB/s minimum speed required for most 4K recording.
U3 vs. V30: Is there a difference? No, for practical purposes, they mean the same thing: 30 MB/s minimum write speed. Most modern U3 cards are also certified as V30.
3 Application Performance Class (A-Class): For Apps & Gaming
This rating is different: it measures a card's speed in **random read/write operations (IOPS)**, not just sustained writes. This is critical for running applications and games directly from the card.
A1
The original standard. Good for storing apps on Android phones.
A2
Significantly faster random performance. **Highly recommended for handheld gaming consoles like the Steam Deck and Nintendo Switch** for faster game load times.
Who needs this? Anyone using a microSD card to expand storage for apps or games on a phone, tablet, or handheld console.
Bus Interface: UHS-I vs. UHS-II
The bus interface refers to the physical pins on the card that transfer data. This determines the card's maximum theoretical speed.
UHS-I (Max ~104 MB/s)
Has one row of pins. This is the most common interface, found on the vast majority of SD cards and devices. It's more than enough for most users, even with V30 cards.
UHS-II (Max ~312 MB/s)
Adds a second row of pins for dramatically faster read/write speeds. This is essential for V60 and V90 cards and allows professionals to offload footage from their card to a computer much faster.
Do I need UHS-II?
You only need a UHS-II card if **both your card AND your device (camera/reader) are UHS-II compatible.** If your camera only has a UHS-I slot, a UHS-II card will work but at slower UHS-I speeds. Check your camera's specifications. A UHS-II card is a must for V60/V90 ratings.
Card Recommendations by Device
Mirrorless & DSLR Cameras
- Standard 4K Video: V30 / U3, UHS-I
- RAW Burst Photography: V60, UHS-II (to clear buffer faster)
- High-Bitrate Video (10-bit, All-I): V60 / V90, UHS-II
Drones & Action Cameras (GoPro, DJI)
- MicroSD Card Type: V30 / U3, A2 rating is a plus.
- Check manufacturer's recommended list, but V30 is a safe bet for all 4K modes.
Handheld Gaming (Steam Deck, Switch)
- MicroSD Card Type: A2 rating is the top priority for fast game loading.
- V30 / U3 is also recommended. Look for cards marketed as "For Gaming".
Smartphones & Tablets
- MicroSD Card Type: A1 or A2 for apps.
- U1 is fine for general storage. U3 / V30 if you record a lot of 4K video directly to the card.
Frequently Asked Questions
What happens if my card is too slow for my video recording?
Your camera will likely stop recording automatically after a few seconds. The camera's internal buffer overflows because the card can't write the data fast enough. You may also see a "Recording Stopped" error message or experience "dropped frames," resulting in choppy, unusable footage.
Is V30 the same as U3?
Yes, for all practical purposes, they both guarantee a minimum sustained write speed of 30 MB/s. The V30 is just a newer certification from the SD Association, specifically for video. If a card is rated U3, it meets the requirement for V30. Most modern U3 cards are dual-rated with the V30 logo as well.
Why is my "170 MB/s" card slow?
The large number printed on the front is the **maximum read speed**, not the sustained write speed. This speed is only achieved in short bursts when reading data (like transferring files to a computer). For recording video, the V-Class or U-Class rating (e.g., V30) is the number that truly matters, as it's the guaranteed minimum speed.
Do I need a UHS-II card for 4K video?
Not usually. Most standard 4K video can be recorded perfectly on a V30 UHS-I card. You only need a UHS-II card if you are shooting very high-bitrate video (requiring a V60 or V90 rating) or if you are a professional who wants to significantly reduce the time it takes to transfer large files from your card to your computer.
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