What is a Class 4 or higher micro SD card?

What is a MicroSD Card?

A microSD card, also known as a microSDHC or microSDXC card, is a type of removable flash memory card used for storing information in small, portable devices such as mobile phones, tablets, and digital cameras 1. The microSD format was introduced in 2005 as a smaller variant of the standard SD card format.

Physically, microSD cards are very small, measuring just 15 x 11 x 1 mm (0.59 x 0.43 x 0.04 in), and weighing under 1 gram. They are about a quarter of the size of a full-size SD card. Despite their tiny size, microSD cards provide significant storage capacity, ranging from 128MB up to 2TB for the latest microSDXC cards.

Due to their compact size and high storage capacity, microSD cards are commonly used as removable storage in small, portable devices where space is at a premium, like smartphones, action cameras, drones, handheld gaming systems, and tablets. This allows you to easily transfer files between devices and expand the internal storage capacity of your device.

MicroSD Card Speed Classes

All MicroSD cards are assigned a speed class rating that indicates the minimum write speed they are guaranteed to sustain. The SD Association has defined several speed classes for SD and MicroSD cards to help consumers identify cards that meet their minimum performance requirements.

The main speed classes for MicroSD cards are:

Class 4 – Minimum sustained write speed of 4 MB/s (SD Association)

Class 6 – Minimum sustained write speed of 6 MB/s (Expert Reviews)

Class 10 – Minimum sustained write speed of 10 MB/s (Kingston)

Higher speed classes indicate better performance, with Class 10 cards being the fastest mainstream option. The speed class rating is important for uses that involve continuous writing like shooting high-resolution photos or video.

Class 4 MicroSD Cards

Class 4 MicroSD cards have a minimum write speed of 4MB/s according to the SD Association’s speed class rating system (Source). This means Class 4 cards are guaranteed to sustain a minimum write speed of 4 megabytes per second.

The Class 4 speed rating makes these cards well-suited for standard definition 720p video recording. 720p HD video has a resolution of 1280 x 720 pixels and a frame rate of 30fps, requiring a bitrate around 3-5Mbps. Class 4 MicroSD cards can reliably handle this bitrate for smooth 720p video capture and playback (Source).

However, Class 4 cards may struggle with 1080p full HD video which has higher resolution and bitrates. For 1080p recording, Class 6 or Class 10 cards are recommended. But for 720p HD video, Class 4 MicroSD cards offer a balance of adequate performance and value.

Class 6 MicroSD Cards

Class 6 microSD cards have a minimum write speed of 6MB/s according to the SD Association’s speed class rating system (https://www.sdcard.org/developers/sd-standard-overview/speed-class/). This means the card is guaranteed to sustain a minimum write speed of 6MB per second.

A Class 6 rating makes these cards a good choice for recording 1080p full HD video. Recording 1080p video requires a sustained write speed of around 6-10MB/s, which falls within the capabilities of a properly functioning Class 6 microSD card (https://www.kingston.com/en/blog/personal-storage/memory-card-speed-classes). Using a lower class card may result in choppy or truncated video recordings.

In summary, Class 6 microSD cards are ideal for 1080p full HD video recording and provide smoother performance compared to lower class cards. Just make sure to buy from a reputable brand and check reported speeds to ensure it meets the minimum 6MB/s write performance.

Class 10 MicroSD Cards

Class 10 MicroSD cards have a minimum write speed of 10MB/s, according to Kingston[1]. This speed class is designed for more intensive tasks like 4K video recording[2].

Class 10 cards offer significantly faster speeds than lower classes like Class 4 or Class 6. The 10MB/s minimum write speed enables smooth 4K video recording, which requires write speeds of at least 6-8MB/s[3]. Class 10 cards are recommended by leading camera manufacturers for capturing high-resolution 4K and HD video[2].

Overall, the Class 10 designation indicates the card can sustain a minimum sustained write speed of 10MB/s. This makes them well-suited for high bitrate tasks like 4K video, HD video, high-res photography, and gaming applications.

[1] https://www.kingston.com/en/blog/personal-storage/memory-card-speed-classes
[2] https://www.wired.com/story/sd-card-speeds-explained/
[3] https://www.sdcard.org/developers/sd-standard-overview/speed-class/

MicroSD Card Read Speeds

The read speed of a microSD card determines how fast data can be transferred from the card. Read speeds are measured in megabytes per second (MB/s) or megabits per second (Mb/s). Faster read speeds allow for quicker transfer of photos, videos, apps, and other files to and from the microSD card.

Max read speeds vary considerably across microSD speed classes:

  • Class 4 cards have max read speeds of 4 MB/s
  • Class 10 cards can reach 10 MB/s read speeds
  • UHS Speed Class 1 (U1) supports up to 10 MB/s read
  • UHS Speed Class 3 (U3) hits minimum 30 MB/s read
  • Video Speed Class 30 (V30) guarantees 30 MB/s sustained read

So a U3 or V30 microSD will have much faster read performance than a Class 4 or 10 card. This is important when transferring large files like 4K video, RAW photos, or game data. The faster read speed means less time waiting for transfers to complete.

For example, a 100MB 4K video would take roughly 10 seconds to transfer from a Class 10 card, but only 3 seconds with a U3 card. This time savings adds up when handling many large files (Kingston).

Overall, microSD cards with faster maximum read speeds provide a big boost to real-world usage and file transfer performance.

Impact on Device Performance

Faster MicroSD cards can improve the overall speed and performance of devices like smartphones and tablets. Using a card with higher read/write speeds allows the device to access data from the card more quickly.

With a faster Class 10 or UHS-1 card, many users report reduced app lag and smoother system performance compared to slower Class 4 cards. The improved MicroSD card speeds allow for quicker loading of apps, documents, photos and videos stored on the card. This also enables better multitasking capabilities when using multiple storage-intensive apps at the same time.

According to one Reddit discussion, upgrading from a Class 4 to a Class 10 MicroSD card resulted in apps opening twice as fast. The consensus is that MicroSD card speed can directly impact overall device speed and responsiveness when the card is in use.

Price Differences

Class 10 microSD cards generally cost more than lower speed cards like Class 4 or Class 6.[1] This is because higher speed cards utilize faster memory chips and more advanced controllers, which increase manufacturing costs. According to Bulk Memory Cards, a 16GB Class 10 card may cost around $5-10 more than an equivalent Class 4 card.

However, there are diminishing returns on speed as you go up through the classes. While a Class 10 card offers a significant speed boost over a Class 4, the difference between a Class 10 and a newer Class A1 or A2 is much smaller. But the prices continue to rise. So for many devices a Class 10 card offers a good balance of speed and value.

Top MicroSD Card Brands

When looking for a reliable microSD card, some of the top brands to consider include SanDisk, Samsung, Lexar, and Kingston.

SanDisk is one of the leading manufacturers of microSD cards and is known for making high-quality and durable products. Their cards come with warranties ranging from 10 years to lifetime limited depending on the model. Models like the SanDisk Extreme Pro are designed to withstand extreme conditions.

Samsung also produces excellent microSD cards that are fast, reliable, and come with 10 year limited warranties. Their PRO Plus and EVO Select lines are top-rated for performance. According to The New York Times, the Samsung Pro Plus is one of the best performing microSD cards available.

Other brands like Lexar and Kingston offer more budget-friendly options that still deliver good speeds and performance. Their cards typically come with 3-5 year warranties. While not as fast as premium brands, they provide decent value for casual users.

When choosing a microSD card for an important device like a camera or phone, investing in a reliable brand with a strong warranty can give peace of mind and ensure your data is protected.


In summary, the key differences between microSD speed classes are:

  • Class 4 cards have minimum read speeds of 4 MB/s and are suitable for basic tasks like music playback.
  • Class 6 cards offer minimum read speeds of 6 MB/s, good for point-and-shoot cameras and some apps.
  • Class 10 cards have minimum read speeds of 10 MB/s and provide good performance for Full HD video recording.

When choosing a microSD card, consider the device you intend to use it with and the types of tasks you’ll be performing. For basic functionality, a Class 4 card should suffice. For recording or transferring HD video, a Class 10 card is recommended for optimal speed and performance.

Higher speed cards tend to be more expensive, so only opt for Class 10 if you truly need those transfer rates. Look at the capabilities of your device, and buy the fastest card its SD slot can support. Major brands like SanDisk, Samsung and Sony make reliable, high-quality cards across all speed classes.