SIM cards come in several standard sizes. Each newer type has been made smaller to save space inside phones and other connected devices, while still holding the same basic subscriber information.

The full size SIM (sometimes called 1FF) is the original, credit card sized format. It measures about 85.6 millimetres long, 53.98 millimetres wide and 0.76 millimetres thick. This format is rarely used in modern phones and was mostly seen in very early mobile devices and some older equipment.

The mini SIM (2FF) was the first “small” SIM most users became familiar with. It is much more compact than the full size card, with dimensions of 25 millimetres by 15 millimetres and a thickness of 0.76 millimetres. Many phones from the 2000s and early smartphones used this size. When people say “standard SIM” in older guides, they usually mean this mini SIM.

The micro SIM (3FF) made the card even smaller to free up more internal space for batteries and hardware. A micro SIM measures 15 millimetres in length, 12 millimetres in width and keeps the same 0.76 millimetre thickness. This type was common in smartphones around the early 2010s.

The nano SIM (4FF) is the smallest physical SIM card widely used today. It reduces almost all of the plastic around the chip, with dimensions of 12.3 millimetres by 8.8 millimetres and a slightly thinner profile of 0.67 millimetres. Most modern smartphones use nano SIM cards, or rely on an eSIM (embedded SIM) which is built directly into the device without any physical card at all.