This article was inspired by a recent discussion with SanDisk experts about the confusion surrounding SD cards—specifically their different types, speed ratings, and labels. If you’ve ever felt overwhelmed by terms like SDHC, UHS-I, or Class 10, you’re not alone.
By the end of this guide, you’ll know:
The different types of SD cards and their uses
How speed ratings affect performance
How to choose the best card for your camera
What Are SD Cards?
In 2000, SanDisk, Panasonic, and Toshiba established the SD Association to create a universal memory card standard for consumer electronics. Today, SD cards come in three physical sizes:
1. Standard SD (24mm × 32mm, 2.1mm thick) – The most common type, used in everything from compact cameras to professional DSLRs.
2. miniSD (20mm × 21.5mm, 1.4mm thick) – Once popular in phones, now mostly replaced by microSD.
3. microSD (11mm × 15mm) – Tiny but powerful, commonly used in smartphones and action cameras.
SD, SDHC, and SDXC: What’s the Difference?
The SD Association defines three main capacity-based categories:
SD: Up to 2GB (older, rarely used today).
SDHC: 2GB–32GB (common in mid-range devices).
SDXC: 32GB–2TB (best for high-resolution photos and 4K video).
Speed Classes: Why They Matter
SD cards have minimum sustained write speeds to ensure smooth performance, especially for video recording. Here’s how they break down:
Standard Speed Classes (for video recording)
Class 2: 2MB/s
Class 4: 4MB/s
Class 6: 6MB/s
Class 10: 10MB/s
UHS Speed Classes (faster performance)
UHS-I (U1): 10MB/s minimum
UHS-II (U3): 30MB/s minimum
Note: The speed class (e.g., Class 10) is different from the card type (SDHC/SDXC).
Why Speed Matters for Photography
Video recording requires a minimum sustained speed (hence speed classes).
Still photography benefits from maximum write speeds—especially for burst mode shooting.
The Diner Metaphor
Think of your camera as a chef and your SD card as a waiter:
A slow waiter (slow card) means the chef (camera) gets backed up, delaying shots.
A fast waiter (fast card) keeps up with rapid shooting, preventing bottlenecks.
Manufacturer Speed Ratings
Some cards advertise maximum speeds (e.g., 90MB/s) rather than just the minimum. For photographers:
Write speed = How fast the camera saves photos.
Read speed = How fast you can transfer files to a computer.
Choosing the Right Card for Your Camera
Check your camera’s manual for compatibility (SD/SDHC/SDXC).
For video, match the recommended speed class (e.g., Class 10 for 4K).
For burst photography, prioritize high write speeds (e.g., 45MB/s+).
Backward Compatibility
Newer devices support older cards (e.g., an SDXC camera can use SDHC/SD cards).
Older devices don’t support newer cards (e.g., an SDHC camera won’t recognize SDXC).
Warning: Formatting an SDXC card in an SDHC device can permanently downgrade it.