Currently, there are 3 SIM card sizes available on the market - standard, micro and nano. In addition, there are some handsets that can use an eSIM. An eSIM is a digital SIM that allows you to activate a cellular plan without having to use a physical SIM. Newer I Phones such as the iPhone XR and XS along with the iPad Pro are eSIM compatible. Getting back to the physical SIM cards, and just to add to the confusion, the standard SIM card size is sometimes referred to as a "mini" SIM. All iPhone 5 and iPhone 6,7,8 and the X models take the nano SIM card and many of the older Samsung phones, such as the 4,5 and 6 use a micro SIM card but the newer ones such as the Samsung s8 and the s9 use a nano SIM. Most phones that are not smartphones use the standard size. For many other popular iPhone, Samsung and Nokia models, please see below.
We are often asked why there are different sizes as the sizes are quite nominal. While the official word is not out, it seems unlikely that the reason is to save space for more memory or other internal features in a phone (although oftentimes, that is the "official" reason manufacturers state). Rumor has it that by having three different sizes of SIM cards, this increases the chances that you will not find or figure out what SIM card size you need for your phone or you will get the wrong size and hence, will end up having to roam with your provider. Good for them, bad for you. Cellular Abroad has gotten around this problem by selling 3-1 SIM cards that will snap down to any of the needed sizes. If your SIM card size is not in the chart below, please ask your carrier or simply use Google to find out what SIM card size your phone requires.
Please note that standard and mini are one in the same.