What Are SD Card Speed Class, How Do You Test It [Full Guide]

Sherly updated on Feb 22, 2023 | Home >Computer Instruction

Memory access times vary significantly from one brand and model of Secure Digital (SD) memory card to another. Speed differences make it hard to determine with certainty which card is capable of recording live-streaming media. 

Now, let's dive into learning what SD card speed class is.

What Is SD Card Speed Class

In response to a need for high-quality video recording, the SD Association has established several Speed Class specifications. Users can determine the most trustworthy mix of host and card items by looking at the Speed Class icons (no frame drop).

You'll see a jumble of different specifications and symbols on the SD card's label. However, only a select few speeds are relevant, and you may be able to disregard them altogether if companies publish their cards' speeds.

We'll start with the Speed Group. A C sign enclosing a numeric value denotes this. The highest rating on current SD cards is 10, making it the best in its class. Class 10 cards can transfer data at a rate of at least 10 MB per second. It seems obsolete because modern cards can reach speeds much above what this icon represents. Keep a lookout, though, because you never know when you might stumble onto an older card with a lower Speed Class number.

sd card speed class

The next category is the UHS Speed Class, which is the most practical. Only two of them exist, designated U1 and U3. U3 cards need to be at least 30 MB/s in speed, while U1 cards need only 10 MB/s. They can do much more than you think in either instance. These are typically represented by the numerals 1 or 3 enclosed in a U.

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Adding to the confusion, there's also the UHS bus variety. These are particularly pertinent for ultra-fast SD cards. The theoretical ceiling for UHS-I cards is 104 MB/s, whereas the ceiling for UHS-II cards is 312 MB/s. Those are merely the maximum transfer rates of the connector, not necessarily the actual transfer rates of the devices being connected. A UHS-II card is what you want if you need to conduct intensive tasks like recording 6K or 8K video. A standard convention is using Roman numerals I or II to denote these.

sd card speed class

The last category is Video Speed. These are indicated by the letter V followed by a minimum write speed expressed in megabytes per second. Five different velocity levels (V6, V10, V30, V60, and V90) are available. A V6 card, for instance, has a guaranteed minimum write speed of 6 MB/s. It's evident that there are faster cards, but this is a nice benchmark to keep an eye out for.

Remember that these signs are all simply beginning points. Actual speeds are typically listed on the product page or packaging if not printed directly on the card itself. Always double-check, as there may be a significant performance gap between the card's minimum ratings and its actual speed. In the next part, you can get a reliable tool to help you test the true and real-time speed.

Professional Tool to Test SD Card Speed Class Efficiently for You

The free version of EaseUS Partition Master is a powerful and reliable Windows formatting utility. Microsoft Windows 11, 10, 8, 8.1, and 7 are only some of the versions it is compatible with. With its help, you can easily get how fast your SD card is.

Free Download 

Windows 11/10/8/7100% Secure

Here are the steps:

Step 1. Launch EaseUS Partition Master. And click the download button to activate the "DiskMark" feature under the "Discovery" section.

click the download button of diskmark

Step 2. Click on the drop-down box to choose the target drive, test data, and block size.

select a drive

Step 3. Once everything is configured, click "Start" to begin the disk test. Then, you can see the Sequential or Random read/write speed, I/O, and Delay data.

click start

Is there anything else EaseUS Partition Master can do to aid in SD card issues? Sure!

This software does little more than manage files on your hard drive, and it's built into Windows. It's the best tool to test SD card speed efficiently. The following are some of its features:

Get EaseUS Partition Master and try it out right now! Using it, you won't have to worry about organizing your discs or other external hard drives.

Free Download 

Windows 11/10/8/7100% Secure


The SD card is defined, and its speed class is discussed in this article. The following section may be helpful if you have further inquiries regarding the SD card. However, EaseUS Partition Master is one of the best third-party tools to test SD Card speed efficiently for you. There are some other links related to SD cards, so you can click them if you need help.

SD Card Speed Class FAQs

In the following section, we've compiled answers to some of the more frequently asked questions.

1. What are the speed classes of SD cards?

There are four ratings within the C-Class:

  • C2 (Class 2): minimum write speed of 2MB/s.
  • C4 (Class 4): minimum write speed of 4MB/s.
  • C6 (Class 6): minimum write speed of 6MB/s.
  • C10 (Class 10): minimum write speed of 10MB/s

2. Is UHS 1 or 3 better?

Unlike UHS Speed Class 3, which allows at least 30MB/s write speed, UHS Speed Class 1 only supports a minimum of 10MB/s write speed. You can tell what class of UHS speed it is by looking for a 1 or a 3 inside the U symbol for a bucket. In general, a U3-rated SD card is required for 4K-capable camcorders.

3. What are the 4 types of SD cards?

There are now four sub-types of secure digital cards (all of which are generally known as SD cards): SD, SDHC, SDXC, and SDUC.

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Updated by Sherly

Sherly joined EaseUS in 2022 and she has always loved writing articles and enjoys the fun they bring. She receives professional training here, focusing on product performance and other relative knowledge.

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