SIM cards come in four sizes, Standard, Regular (Mini), Micro, Nano.
This is the original SIM card size, which is the same size as a credit card. Virtually no phone made in the last 15 years accepts this size SIM card.
Regular (mini) SIM
Regular (mini) is for most older and basic phones, including Apple iPhone 3G and iPhone 3GS. This SIM card is officially called a mini SIM (to differentiate it from the much larger standard SIM that was commonly used when the mini SIM was first introduced), although it is now the largest SIM card still in use and is commonly referred to as a regular size SIM card. The SIM measures 25mm x 15mm.
Micro size SIM cards fit the Apple iPhone 4/4S, BlackBerry Q5/Q10/Z10/9720, LG Google Nexus 4, Samsung Galaxy SIII/S4/S5/Note II, HTC One/One X, Nokia N8/Lumia phones as well as the Apple iPad (generations 1–4). The micro SIM measures 15mm x 12mm.
Nano SIM cards fit the Apple iPhone 5/5C/5S/6/6 Plus/SE/7/7 Plus, Motorola Moto X and some newer Samsung Galaxy smartphones plus the Apple iPad Air, Apple iPad Pro and iPad Mini. The nano SIM measures 12mm x 9mm.