RAM Type: PC3-12800 DDR3L Min. RAM Speed: 1600 MHz
Details: Supports 1600 MHz PC3-12800 DDR3L SDRAM SO-DIMMs (204-pin).
Standard RAM: 8 GB Maximum RAM: 16 GB*
Details: 8 GB of RAM is installed as two 4 GB modules, no slots free.
*Apple officially supports a maximum of 8 GB of RAM, but third-parties have determined that this model actually is capable of using up to 16 GB of RAM with two 8 GB memory modules.
As mentioned by Mayer above, the max official capacity is 16GB and the MacBook Pro itself can support up to 32GB unofficially. Here's the catch.
If you spend 100s of bucks just the sake of upgrading to the unofficial maxed out 32GB memory, in real world experience for basic application uses, you wold not see any significant speed perform. I would say you won't see any speed boost at all.
If you are rendering movies, editing RAW images or something like that, you will see smooth operation after 32GB memory upgrade for sure. Just make sure that if you need 32GB unofficial upgrade, try keeping your computer cool along heavy app operation and workflows. You will not only void warranty, also risk frying up fixed clocked Intel.