How do you choose RAM for your Apple MacBook?
SODIMM form factor
SODIMM is a compact form factor RAM memory. It's more compact than DIMM and also the only form factor that fits in a MacBook. This is the first step you should consider when choosing RAM for your MacBook.
Note the DDR standard
There are currently 2 RAM standards available: DDR3 and DDR4. This indicates the speed of the memory. DDR3 is the only type of RAM that works with an Apple MacBook where you can replace the memory. DDR4 is suitable for iMacs from 2017. Therefore, make sure that you don't accidentally purchase DDR4 RAM for your MacBook.
Clock speed of the RAM
The clock speed also plays a role in the speed of the RAM. This is expressed in Megahertz (MHz) and must match the speed that your MacBook supports. If you want to replace the memory of a MacBook that, for example, supports 1600MHz, you must install RAM modules with a speed of 1600MHz. A higher or lower speed doesn't work, so make sure that the speeds are the same.
Check how much space you have for extra memory
MacBooks up to and including those from mid 2012 have space for 2 memory slots that fit a RAM module. The RAM is often divided into 2 slots by default, so when upgrading your MacBook you have to replace both RAM modules.
Note: with MacBooks from late 2012 and later, it's not possible to expand the RAM. It's soldered onto the motherboard.