SD card classes explained

Different types of SD card class specify the performance of the card in different operations.

Application Classes A1, A2

The application performance class designations A1 and A2 specify the performance of a card with small files. For use in a Raspberry Pi, or as application storage in a mobile phone, the operating system will make very many read and write operations with very small files. Finding and reading/writing small files quickly requires different optimisation in the SD card compared with writing large files quickly. The Raspberry Pi SD interface will be able to take advantage of A2 class performance.

Class A1 and A2 are defined by:

Speed classes C10, U3, V30

The main speed classes refer to the sequential read or write speed. The sequential speed is important for writing and reading large files, like photos or videos. Video is particularly demanding because you need to write fast and continuously. The fastest common video class designation is V30 - meaning sustained write speeds of 30MB/s. Another set of speed standards are the U classes, with U1 being 10MB/s and U3 being 30MB/s. Many cards separately specify a maximum read or write speed that is very much faster than 30MB/s, possibly more than 100MB/s. The Raspberry Pi SD interface will be able to take advantage of up to about 50MB/s.

Recommendation for a Raspberry Pi

The official Raspberry Pi SD cards (2025) specifications are in the product brief