Standard SIM, Micro-SIM and Nano-SIM

The standard SIM is the most commonly used SIM in phones. It's around two and a half centimetres long, and one and a half centimetres wide.

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. Many other phones also use micro-SIMs.

A nano-SIM is around 40% smaller than a micro-SIM. You'll need a nano-SIM if you're using iPhone 5, 5s or 5c

Nano SIM refers to the SIM (Subscriber Identity Module) standard used by the cellular capable iPad models - the iPad Air (Wi-Fi/Cellular), iPad mini (Wi-Fi/AT&T/GPS), iPad mini (Wi-Fi/Verizon & Sprint/GPS), and iPad mini (Retina/2nd Gen - Wi-Fi/Cellular) -- as well as all iPhone 5, iPhone 5c, and iPhone 5s models.

Nano SIM is the fourth version, or the "fourth form factor" (4FF) of the SIM standard and measures a mere 12.3 mm by 8.8 mm by 0.67 mm, but still holds the same amount of data as earlier SIM cards.

Nano SIM is both smaller and approximately 15% thinner than the earlier Micro SIM (3FF) standard as well as the Mini SIM (2FF) cards that were ubiquitous for many years and people commonly refer to simply as SIM cards. Technically, the original SIM (1FF) card standard is the same size as a credit card and most people probably have never seen one in person.