There isn't really a set rule about how much RAM you need for a laptop. Some laptops come with 2GB of RAM, some come with 4GB, and others come with 6GB.
It just depends on what you plan on doing with your laptop. Others come with 8GB and some even have much larger RAMs.
For example, if you only use your laptop to surf the internet, read e-books, write documents, and listen to music, then you probably don't need anything more than 2GB of RAM.
On the other hand, if you plan on playing video games, watching movies, editing photos, or using Photoshop, then you'll definitely need more RAM.
So before buying a new laptop, check out its specs first. Look at the RAM, processor, hard drive size, battery life, and everything else. Then decide whether you need more RAM or not.