Bitcoin.org suggests the following minimum system requirements:

• Desktop or laptop hardware running recent versions of Windows, Mac OS X, or Linux.
• 145 gigabytes of free disk space
• 2 gigabytes of memory (RAM)
• A broadband Internet connection with upload speeds of at least 400 kilobits (50 kilobytes) per second
• An unmetered connection, a connection with high upload limits, or a connection you regularly monitor to ensure it doesn’t exceed its upload limits. It’s common for full nodes on high-speed connections to use 200 gigabytes upload or more a month. Download usage is around 20 gigabytes a month, plus around an additional 140 gigabytes the first time you start your node.
• 6 hours a day that your full node can be left running. (You can do other things with your computer while running a full node.) More hours would be better, and best of all would be if you can run your node continuously.