All SIM cards are not the same size. As of 2015, when a SIM is purchased, it comes attached to the card with a code written on it. The sizes range from mini to nano.
Mini was the most common SIM card size but was outdone by the micro cards. These cards are found in most lower-end Android smart phones, as of 2015.
The micro SIM card is slightly shorter than the standard size but still has enough room to keep its chip-set protected.
The nano SIM card is the smallest variant, as of 2015. These cards are generally found in high-end phones.