Digital cameras, smartphones, dashcams, and many other devices use SD cards.
However, with so many different capacities, speeds, and standards, many people feel lost and don’t know which one to choose. This article will provide a clear explanation of SD card standards and how to choose the right one for you.
We will organize the points that are easy to get confused about when choosing, such as capacity, speed, compatibility, and durability, and show the criteria for making decisions based on your intended use. Whether you are a first-time buyer or considering a replacement, acquire the knowledge to avoid making mistakes.
What you will learn in this article!
What is an SD card?
An SD card is a small storage device that uses flash memory with a common standard.
It is used in a wide range of devices, including digital cameras, action cameras, drones, dashcams, portable game consoles, and smartphones (microSD). The first thing you should know is the four “axes” in the world of SD cards.
- Shape (external form): SD / microSD
- Capacity logo: SD / SDHC / SDXC / SDUC (＝the division of the maximum usable capacity)
- Minimum guaranteed speed: Speed Class (C / UHS / Video)
- Upper limit of speed: Bus interface (High Speed / UHS-I / UHS-II…)
As we will discuss in detail in the following chapters, the most important points to consider when choosing are the “capacity logo” supported by your device and the “minimum write speed” required. If you miss this, the card may not perform to its full potential, or may not work at all.
Shape (SD / microSD)
- SD (standard size): 32 × 24 × 2.1 mm. Mainly used in interchangeable-lens cameras, video cameras, and PC card readers.
- microSD: 15 × 11 × 1.0 mm. Designed for small devices such as smartphones, action cameras, drones, and portable game consoles. It can be used with an SD slot using the included adapter.
- Single-lens/mirrorless cameras: Basically use an SD slot. An SD size is easier to handle in terms of card rigidity and ease of use.
- Small cameras/mobile devices: If the main body has a microSD slot → microSD only. Connect to a PC with an adapter if necessary.
SD card “speed” has a two-layer structure
The speed markings on SD cards may seem complicated, but they are divided into two layers with different purposes.
- Speed Class (＝indicator of recording stability)
Class markings such as C10 / U1・U3 / V30・V60・V90 guarantee “at least this speed can be written”. This is critical for video recording. - Bus interface (＝theoretical upper limit)
The higher the stage, such as High Speed / UHS-I / UHS-II…, the faster the burst writing and PC transfer will be. However, the speed will be limited if the device, card, and reader do not all have the same grade.
M. GadgetFor example, if you insert a UHS-II card into a camera or reader that supports UHS-I, it will only operate at the UHS-I upper limit.
What is Speed Class: Minimum guarantee for stable video recording and continuous writing
SD cards have class marks such as “C”, “U”, and “V”. This is a standard that guarantees “at least this speed can be written”, and is directly related to the stability of video recording in particular.
- Speed Class (C): C4 = 4MB/s, C10 = 10MB/s
- UHS Speed Class (U): U1 = 10MB/s, U3 = 30MB/s
- Video Speed Class (V): V30 = 30MB/s, V60 = 60MB/s, V90 = 90MB/s
- SD Express Speed Class (E): E150 = 150MB/s, E300 = 300MB/s, etc.
- Full HD video: C10 / U1 / V10 is often sufficient
- 4K video: U3 / V30 is a common minimum requirement
- 8K video/All-Intra: V60 / V90 recommended (subject to device requirements)
What is Bus Interface: A standard that determines the theoretical maximum speed
The bus interface determines how fast data can be exchanged between the card and the device. This indicates the “maximum speed frame”, but is separate from recording stability.
| Bus standard | Terminal shape | Theoretical upper limit | Main features |
|---|---|---|---|
| UHS-I | Single-stage | 104MB/s | Current standard standard |
| UHS-II | Dual-stage | 312MB/s | Faster burst and transfer |
| UHS-III | Dual-stage | 624MB/s | Rarely available on the market |
- The speed does not increase if all of the card, device, and card reader do not support the same standard
- If you insert a UHS-II card into a device or card reader that supports UHS-I, it will operate at the UHS-I speed.
What is capacity standard: division of the maximum storage capacity
SD cards have a fixed name and logo for each capacity band. This is not just a difference in size, but also includes the file system format and rules for compatibility.
- SD: Up to 2GB
- SDHC: Over 2GB to 32GB (mostly FAT32)
- SDXC: Over 32GB to 2TB (mostly exFAT)
- SDUC: Over 2TB to a maximum of 128TB (exFAT assumed)
- If the card’s logo is greater than or equal to the device’s support, it will not work (e.g., SDXC cards cannot be used with SDHC-only devices).
- If the device supports a higher grade, a lower grade card can be used (e.g., SDXC-compatible devices can use SD/SDHC/SDXC).
- If in doubt, check the “supported logo” in the device’s instruction manual.
Typical uses and indicators that are often needed
- Photo-centric (RAW + burst): UHS bus and UHS-II are effective. A minimum write speed of C10/U1 is often sufficient, but a faster interface can reduce waiting time after burst shooting.
- Video-centric (FHD/4K/8K): Minimum write speed (U3 or V30～V90) is key to stability.
- Smartphone expansion: A1/A2 (application performance class).
- Surveillance/dashcam: High durability and ample capacity.
- Game console: UHS-I is often assumed, and capacity is important.
What is Application Performance Class: For smartphones and app usage
For running apps and saving game data on smartphones and tablets, random access performance is effective. The A1/A2 mark indicates this.
| Standard | Random read | Random write | Sequential write |
|---|---|---|---|
| A1 | 1,500 IOPS | 500 IOPS | 10MB/s |
| A2 | 4,000 IOPS | 2,000 IOPS | 10MB/s |
Note: To take advantage of A2 performance, the device must support command queuing and caching functions. In some cases, A1 may be more stable if it is not supported.
First, decide here (introduction check)
- Capacity band supported by the device (SD / SDHC / SDXC / SDUC)
- Intended use (photo/video resolution, bit rate, continuous recording, smartphone expansion)
- Required minimum write speed (C / U / V)
- If you want to shorten burst and transfer times, consider UHS-II or higher bus.
M. GadgetSolidifying these four points in advance will make it easier to narrow down your options.
- Capacity logo compatibility and minimum write speed determine whether it “can be used” and “recording will be stable”.
- Look at the class mark rather than the “maximum speed” number to ensure stable recording.
How to choose an SD card
Key points of this heading!
- Capacity: Choose a size that matches your intended use
- Speed: Ensure the necessary transfer performance for your intended use
- Compatibility: Be sure to check the device’s supported standards and logo
- Durability: Choose according to the usage environment
- Price and performance: Determine the necessary specifications
When choosing an SD card, it is easier to proceed by checking the following six criteria in order. If you think in this order, you can naturally narrow down “which one can be used and which one is sufficient”.
Capacity: Choose a size that matches your intended use
Determine the capacity based on “intended use”, “number of shots/recording time”, and “frequency of overwriting”.
- Photo-centric (RAW + JPEG): Approximately 25-50MB per shot.
Approximately 600-1,200 shots on 32GB, and double on 64GB. 64-128GB is recommended for travel. - Video-centric (FHD): Approximately 8-12GB per hour (depending on the bit rate).
Approximately 3 hours on 32GB, and 6 hours on 64GB. - 4K video (30fps, 100Mbps): Approximately 45GB per hour.
Approximately 2.5 hours on 128GB. 256GB or more is realistic for long-time recording.
M. GadgetA large-capacity card is convenient, but the damage from failure is also large. For long-term storage and important recordings, it is also effective to divide the capacity and use multiple cards.
Speed: Ensure the necessary transfer performance for your intended use
Judge the speed by the minimum write speed standard (C/U/V).
- Still image-centric (RAW + less burst): C10 or U1 is often sufficient
- More burst/sports shooting: Minimum U3, also consider UHS-II or higher to speed up buffer clearing.
- Video (FHD): C10/U1/V10-V30 for stability
- Video (4K): U3/V30 or higher is recommended
- Video (8K or All-Intra): V60-V90 recommended (subject to device compatibility)
M. GadgetI think the class mark is more important than the maximum speed number.
Compatibility: Be sure to check the device’s supported standards and logo
- Capacity logo (SD / SDHC / SDXC / SDUC)
- Bus standard (UHS-I / UHS-II…)
- Speed Class (C / U / V)
Durability: Choose according to the usage environment
- Outdoor shooting or travel: Waterproof, dustproof, and temperature resistance
- Car/surveillance cameras: High durability (focus on write endurance)
- Aerial/sports shooting: Shock and vibration resistance
M. GadgetIf you use a low-durability card with a dashcam, the write error may occur after a few months. Durability specifications are insurance for long-term stability.
Price and performance: Determine the necessary specifications
- “Just in case” high specifications can more than double the price
- A level above the performance required for your intended use is a good balance of cost and peace of mind.
- For example, if your main purpose is 4K recording, V30 is often sufficient rather than V60 or higher.
M. GadgetTechnology is advancing day by day, so it’s a shame to buy something unnecessarily expensive 😭
Supplementary terms and specifications
Key points of this heading!
SD (Secure Digital)
A common standard for small storage media using flash memory. Developed by the SD Association.
Features: Small size, removable, and usable with a wide range of devices.
microSD
A smaller version of the SD card (15 × 11 × 1.0 mm). Designed for small devices such as smartphones, action cameras, and drones. It can be used with an SD slot using an adapter.
Summary
Although SD cards may all look the same at first glance, there are many factors that affect performance, such as capacity standard, speed class, bus interface, and durability. To choose the card that is right for your device and intended use, it is important to
- Check the capacity band and logo compatibility
- Understand the minimum write speed required for your intended use
- Check the device’s supported standards
- Choose durability according to the usage environment
This flow is effective.
Determining the “necessary and sufficient performance” will lead to a balance of cost and peace of mind. Before purchasing, double-check the capacity logo, speed mark, and supported standards, and choose the one that is best for your shooting and storage style.
Merci d’avoir lu jusqu’au bout !
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