Memory Cards Explained: How to Choose the Right SD or microSD

Memory cards are covered in confusing symbols. Choosing the wrong one can cause dropped frames, unreliable recordings, or a device that simply refuses to work. Here is what to look at.

Format

• microSD: for phones, tablets, action cameras and dash cams.
• SD: for cameras. An adapter can let a microSD card fit an SD slot.
• CFexpress: for high-end cameras that require extremely fast speeds.

Check which format your device supports and the maximum capacity it can read.

Speed labels

• Class 10: a basic minimum of 10MB per second write speed.
• U1 and U3: UHS Speed Class. U3 guarantees at least 30MB per second.
• V30, V60 and V90: Video Speed Class, often needed for high-resolution video.
• A1 and A2: Application Performance Class, which is relevant for running apps from the card.

Be careful with headline speeds. A card may advertise fast read speeds but have far slower write speeds. For video, the sustained write speed matters.

Picking a card by device

Phones and tablets

A SanDisk Ultra microSD is a sensible option for photos, music and video storage. Note that many flagships and iPhones have no memory card slot. See our storage guide.

Action cameras and drones

Look at SanDisk Extreme, Extreme GO or Extreme PRO cards with a V30 rating or better. High-bitrate cameras have particular requirements. Check your camera manufacturer's approved card list.

DSLR and mirrorless cameras

Choose SD cards with a speed rating suited to your camera. UHS-II cards are beneficial only when your camera supports them. SanDisk Extreme PRO UHS-I and UHS-II are both on our list.

Dash cams and CCTV

These devices constantly overwrite data, which puts wear on cards. Use High Endurance or MAX Endurance cards designed for continuous recording.

microSD Express

These are newer, faster cards for compatible devices, such as the Nintendo Switch 2. Most older devices will not get the full speeds.

Card readers

Fast card readers such as the SanDisk ImageMate PRO, SanDisk Extreme PRO CFexpress reader, and Sony's MRW-G1 and G2 readers speed up transfers from card to computer. Check that the reader matches your card type.

Avoid fakes

Counterfeit cards may report large capacity but fail after storing a small amount of data. Buy from a trusted seller. After purchase, test large cards by filling them and reading the data back.

Backing up

Memory cards can fail without warning. Copy important footage to a computer or portable SSD as soon as possible.