There are three types of SD cards, all of which have different minimum and maximum sizes. Every SD card sold has its capacity labelled on it.
The three types of SD card are SD, which may have up to 2GB capacity, SDHC, which may have more than 2GB and up to 32GB capacity, and SDXC, which may have more than 32GB and up to 2TB capacity. As of 2015, the largest size of an SDXC card is 512GB, according to The Verge. The vast majority of devices support SDHC, but SDXC is newer and less common.
Lexar's website allows you to select a particular SD card type and calculate the remaining capacity of each size after a given amount of photos and/or minutes of video is put on it.