Because dash cams generate large amounts of data, you need to get a high quality of memory card that can adequately store this data.
There is another major measure of memory card quality, and it's called "write speed". The write speed determines how fast it can write video data to the memory card. There are Class 1, 2, 4, 6, 10 of memory card based on different write speed spec.
Make sure you buy a memory card with the appropriate class for your dash cam. The majority of dash cam manufacturers suggest using a Class 6 card or higher.
If you try to record video with a Class 1, 2, or 4 memory card, you may end up with choppy video playback and other incomplete video files.
Here are the reference how long the camera will record HD video before reaching the end of the card:
16GB memory card : 4 – 6 hours
32GB memory card : 6 – 12 hours
64GB memory card : 10 – 20 hours
28GB memory card : 20 – 40 hours
256GB memory card : 40 –80 hours