When it comes to SD cards, one of the key specifications to consider is the MB/s speed rating. This determines how fast data can be written to and read from the card. But does that speed rating really matter? The short answer is: it depends. For some uses, a slower card is just fine, while for others you’ll want the fastest card possible. In this article, we’ll take a deep dive into SD card speeds and when it really makes a difference.
What do the MB/s speeds on SD cards mean?
SD cards have a speed class rating that is measured in megabytes per second (MB/s). This refers to the minimum guaranteed sustained write speed of the card. So for example, a card rated at Class 10 has a minimum write speed of 10 MB/s, while a UHS Speed Class 3 (U3) card has a minimum write speed of 30 MB/s.
Here are some of the most common speed classes for SD cards and their minimum write speeds:
|SD Speed Class||Minimum Write Speed|
|Class 2||2 MB/s|
|Class 4||4 MB/s|
|Class 6||6 MB/s|
|Class 10||10 MB/s|
Faster cards will have higher MB/s ratings. Professional-grade SD cards used for shooting 4K video or high-resolution photos can have speeds up to 300MB/s.
When does SD card speed matter?
In general, higher speed cards are needed for recording or transferring large files, such as:
- 4K and 8K video
- High resolution photos
- High bitrate audio files
- RAW images
- Game installs and loads
Higher speeds allow these large files to be written quickly without having to pause recording or slow down transfers. This is especially important for recording high-bitrate 4K or 8K video. Slower cards may not be able to keep up with the data rate coming from the camera sensor, causing recording to stop.
4K and 8K video recording
When shooting video at 4K or 8K resolution, a fast SD card is essential. 4K video has data rates around 95 MB/s, while 8K video can be up to 130 MB/s or higher. To avoid dropping frames while recording, you’ll want an SD card rated for V30 minimum for 4K, or V60 and higher for 8K.
High resolution photos
High resolution photos from DSLR, mirrorless, and medium format cameras can be 20MB or larger per image. A fast SD card allows you to take photos in quick succession without having to wait for each image to save. Look for U3, V30 or faster cards.
RAW images contain uncompressed image data straight from the camera sensor. The file sizes are much larger than JPEGs. RAW images from high resolution cameras can be 80MB or more. A fast card is needed to quickly save these massive files and shoot continuously.
Game installs and loads
Modern game consoles and gaming PCs use SD cards for installing games and loading during gameplay. The faster the card, the quicker games can install and load new levels and assets. For the best gaming experience, look for SD cards with speeds of 100MB/s or faster.
When is a slower SD card fine?
In many cases, you can get by just fine with a slower SD card with minimal impact:
- Standard HD video (not 4K or 8K)
- Lower resolution photography
- Music and other small files
- General device storage and backup
If you are just shooting regular HD video or lower resolution images from a smartphone or basic camera, a Class 10 or U1 card is sufficient. The smaller file sizes don’t require blazing fast speeds.
Similarly, a slower card works fine for storing documents, music, apps, and other small files that don’t require high data transfer rates. And they can serve as economical storage for backups and general storage purposes.
When does SD card speed not matter as much?
In some cases, the SD card speed is less important or not a factor:
- When device limits speed – Some cameras and devices have a built-in cap on write speeds, so faster cards provide no benefit.
- When shooting timelapse – Timelapse videos have very low data rates since the frame rate is low. A Class 10 card or above should suffice.
- When the device does not support UHS-I – Older devices without UHS-I bus support can’t take advantage of U3/V30 card speeds.
It’s important to check your device specs and requirements before splurging on an expensive high-speed card. Make sure your device supports UHS-I/UHS-II and is capable of actually utilizing those faster speeds.
Does card speed affect photo/video quality?
The speed rating of an SD card does not directly affect the quality of photos or videos. A faster card will not produce higher resolution or less compression than a slower card. However, card write speed can indirectly affect:
- Video frame rates – Slower cards may drop frames in high bitrate 4K/8K footage
- Ability to shoot in burst mode – Faster cards allow more photos in a burst before filling the buffer
- Responsiveness – Less lag time when reviewing photos or waiting for files to save
So while a faster card won’t directly change image quality, it can allow your camera to capture more footage or shots before slowing down.
Does the speed class (10 vs 30) matter if the MB/s is the same?
The speed class (U1 vs U3 for example) specifies the minimum write speed floor. However, two cards from different classes can have the same maximum MB/s rating.
In that case, the actual MB/s speed is more important than class. For example, a U1 and U3 card may both have 100MB/s speeds. The U3 would not have any advantage over the U1 card in that situation, since their top speeds are the same.
However, the class rating provides peace of mind that the card will never dip below a certain performance threshold. So when looking at cards, consider both the speed class and the max MB/s rating.
Is it bad to use a slower SD card if device supports higher speeds?
Generally, no – there is no harm in using a slower SD card in a device designed for faster speeds. The card will simply transfer data at the maximum speed it is designed for. The device may have some lag time as it waits for writes to complete, but there is no damage caused by using a slower card.
However, one exception is using very old cards (Class 2, 4, or 6) in new cameras and devices. These extremely slow cards can sometimes cause issues like freezes, crashes, and other glitches in modern hardware. But Class 10 and above should work fine.
Can you damage a fast SD card by using it in a slow device?
No, using a fast SD card in a slower device will not damage the card. The card will simply operate at the maximum speed supported by the device. The only downside is you won’t be taking full advantage of the card’s speed capabilities.
How to choose the right SD card speed for your needs
Picking the optimal SD card speed for your uses comes down to a few key factors:
- Device requirements – Check device specs for speed class and MB/s recommendations. Aim to match if possible.
- Use case – Will you be recording 4K/8K video? Shooting burst photo? Gaming? Choose appropriate speed.
- Device capabilities – Double check your hardware supports UHS-I/UHS-II and can utilize faster speeds.
- Budget – Faster cards cost more. Slower cards work for many non-demanding uses.
Matching your SD card speeds to your intended use and device capabilities is the best way to ensure optimal performance. But when in doubt, going with a higher class card is generally better.
SD card write speeds, measured in MB/s, indicate how quickly data can be written to the card. Faster speeds are necessary for recording high-resolution 4K/8K video, shooting rapid burst photos, installing games, and working with other large files. For general everyday use like SD video, lower resolution photos, and small files, lower speed cards are usually sufficient.
The speed class (U1, U3, etc) specifies the minimum guaranteed speed, while the MB/s rating indicates maximum speed. Both are important specs to consider when choosing an SD card. Aim to match the recommended speeds for your device and use case for optimal performance. But there is generally no harm using a slower card, beyond some lag time in transfers.
By understanding the different SD card speed ratings and classes, you can select a card with the necessary performance for your needs while avoiding overspending on speed capabilities your camera or device can’t utilize.