SD Card

How to Choose the Right SD Card? Understanding SD Card Specifications



Deciding on the right SD card for your needs can be a daunting task. Whether you are capturing digital photos or recording videos, the SD card plays a crucial role. Despite their familiarity in the digital age, the wide variety of options available can make choosing the right SD card confusing. This guide will help you understand why there can be significant price differences between SD cards of the same brand and capacity and how to select the right one for your needs.

Understanding SD Card Specifications

The full name of an SD card is Secure Digital Memory Card. Whether for capturing digital photos or recording videos, SD cards are indispensable in the digital era. Understanding the two most crucial specifications of an SD card—capacity and write speed—is key to making the right choice.

  • Capacity: Think of capacity as the size of a bucket—the larger the capacity, the more data it can store.
  • Write Speed: Think of write speed as the width of a hose filling the bucket—the faster the speed, the quicker data can be written to the card.

When you look at an SD card, you’ll see various numbers and letters indicating its specifications. These include its storage capacity (e.g., 32GB, 64GB) and speed class (e.g., Class 10, UHS-I, V30). These specifications help determine which SD card is best suited for your needs.

SD Card Capacity

SD cards are categorized based on their storage capacity into three types: SD Standard, SDHC (SD High Capacity), and SDXC (SD Extended Capacity). For most users who capture digital photos and videos, SDHC and SDXC are the more practical options.

Key Differences:

  • SDHC: Supports FAT32 file system, limiting each video file to 4GB. For instance, a 32GB SDHC card will split video files into eight separate 4GB files.
  • SDXC: Supports exFAT file system, allowing continuous recording until the card is full.

Practical Use Cases

  • SDHC Cards: Ideal for moderate photo and video usage, suitable for standard-definition video recording and basic photography.
  • SDXC Cards: Suitable for high-definition video recording (1080p, 4K) and professional photography, allowing for larger file storage without interruption.

Why It Matters: The capacity of an SD card determines how much data you can store, making it essential to choose the right type based on your specific needs and usage patterns.

SD Card Write Speed

The speed of an SD card is divided into read and write speeds. With advances in memory technology, both read and write speeds have improved significantly. Faster read speeds reduce wait times for viewing photos, while faster write speeds are crucial for continuous shooting and high-resolution video recording.

Speed Classes:

  • C (Class): C2 to C10 (2 MB/s to 10 MB/s)
  • U (UHS Speed Class): U1 to U3 (10 MB/s to 30 MB/s)
  • V (Video Speed Class): V30, V60, V90 (30 MB/s, 60 MB/s, 90 MB/s)

Example Comparison:

SD Card Read Speed Write Speed Speed Class
Card A 120 MB/s 10 MB/s U1, Class 10
Card B 95 MB/s 30 MB/s U3, Class 10

Important Note: Write speed is indicated by the number after C, U, or V. For example, U1 means a minimum write speed of 10 MB/s, while U3 means 30 MB/s.

Real-World Applications

  • Class 10/U1 Cards: Suitable for full HD video recording and standard photography.
  • U3/V30 Cards: Required for 4K video recording and burst mode photography.
  • V60/V90 Cards: Best for professional 4K/8K video recording and high-speed photography.

Performance Insight: Faster SD cards reduce lag and ensure smooth recording of high-resolution videos, making them crucial for modern dash cams and cameras.

Video Recording and Storage

The size of video files is influenced by video quality and frame rate. Higher resolution and frame rates result in larger file sizes.

Recording Time by Capacity:

Why It Matters: Understanding how resolution and frame rate affect storage needs helps in selecting the appropriate SD card capacity for your video recording requirements.

Tips for Video Recording:

  1. Match Card Speed to Camera Specs: Ensure the SD card speed matches the requirements of your camera to avoid issues like frame drops or recording interruptions.
  2. Consider Overhead: Always leave some overhead storage to avoid performance degradation when the card nears full capacity.

Photo Storage

The number of photos an SD card can store varies based on factors such as exposure, color, and ISO settings. Here’s an approximate guide for different resolutions and formats (RAW and JPG).

Approximate Storage:

Storage Insights: Higher resolution and RAW formats significantly reduce the number of photos you can store, making higher-capacity SD cards essential for professional photographers.

Practical Advice:

  • JPEG vs. RAW: JPEGs are compressed and smaller in size, making them suitable for casual photography. RAW files retain more detail and are preferred by professionals for post-processing.
  • Burst Shooting: For continuous shooting modes, opt for SD cards with higher write speeds to ensure no data is lost during rapid photo captures.


Choosing the right SD card involves understanding its capacity and write speed specifications. For continuous and high-quality video recording, SDXC cards supporting exFAT file systems are ideal. For high-speed photography and videography, cards with higher write speeds such as U3 or V30 are recommended. Always ensure the SD card matches your device’s requirements to avoid performance issues.