There are three sizes of SIM card:
Your phone's user guide will tell you which size to use, and how to insert it. You can also find out more in our device guides
We use multi-SIMs, which allow you to pop out the size you need for your device. The video below explains how to do this:
If you've just upgraded to a new device, you should keep using your old SIM card. You only have to use the new SIM sent with your upgrade if your old SIM doesn't fit your new device. Find out more in our FAQ on new SIM cards
Find out how to order a replacement SIM for your device.
If you're using an Apple Watch, this has a built-in SIM called an eSIM, so you won't need to use a physical SIM card. However, if you've received a replacement device, you'll still need to activate the new eSIM.