A nano-SIM is around 40% smaller than a micro-SIM and is used in most of the latest devices, including iPhone 6S/6S Plus, and iPhone 7/7 Plus. It’s also used in the Samsung Galaxy S6/S6 Edge, Samsung Galaxy S7/S7 Edge and a number of tablets including the latest iPad models, including the iPad Air, iPad Mini, and iPad Pro.
The micro-SIM is a smaller type of SIM that was first used in the iPhone 4. It's about half the length of the standard SIM. Earlier devices, such as iPhone 4/4S, Samsung Galaxy S4/S4 Mini, Samsung Galaxy S III all use micro-SIMs. A number of tablets also use micro-SIMs, such as the 3rd and 4th generation iPad.
The standard SIM is around two and a half centimetres long, and one and a half centimetres wide. It’s used in older devices, including the iPhone 3GS, Samsung Galaxy SIII Mini, Samsung Galaxy SII, and HTC Desire C.