The Difference Between Speed & Classes In SD/SDHC/SDXC Memory Cards

When purchasing a SD or Micro SD card it is important that you buy one with a suitable ‘Class' rating for your intended use. Common classes range from Class 2 all the way up to Class 10. I personally use a Sandisk Class 10 SD card for my Canon DSLR, but there are many different options out there.
Let me break down what the ‘Speed Class' and ‘Rated Speed' really mean below:

Rated Speed

The maximum speed that is capable of the card and what you would expect to see throughout typical use. When taking high resolution photos, you want a high rated speed to ensure that your able to save your files quickly and have the card be instantly ready to snap another photo. If this speed is too low you will notice very sluggish performance especially if you are attempting to shoot in burst modes with high mega-pixel cameras.


Speed Class

The minimum transfer speeds in a worst case scenario. When your using your card to capture HD video footage, you need this number to be high as these are situations where the device is trying to save a steady stream of data and can get bogged down from the max speeds. If this speed is too low, you can receive dropped frames, lost data, choppy playback, or overall poor performance.

Class vs. Minimum Speed Breakdown

Class 2 – 2MB/s minimum speeds

Class 4 – 4MB/s minimum speeds

Class 6 – 6MB/s minimum speeds

Class 8 – 8MB/s minimum speeds

Class 10 – 10MB/s minimum speeds

I personally recommend buying SD and Micro SD cards from Amazon. They carry a wide selection of cards and have the lowest prices compared to anyone other retailers.

Photo Credit: Dennis S. Hurd