IPhone memory saying full but there's hardly anything on it?

Hi. My iPhone 4s is fairly new so doesn't have many apps on it (it's a 16gb).It's got about 500 photos and 160 videos (about 1 - 2 mins long). My music takes up 2.7 gb. So where has my memory gone? There's really not that much on it but when I try to take a picture it says not enough memory.

Videos and photos, take up A LOT of memory space, don't underestimate how much space they actually take up. You could try deleting some of them or import them to a CD.

You are conflating memory

There's essentially 2 types put simply the physical memory as in a USB stick hard drive [HDD] phone memory… Eg iphone4S 16Gb / 32Gb /64Gb

The memory your phone is stating you are short of is R. A.M memory not PHYSICAL MEMORY, the iPhone4s ONLY has 512 MB

Imaging you have a physical art collection and music collection, comic, collection DVD collection

RAM WOULD BE A VIEWING ROOM, you can only bring so much physical stuff into the room before you run out of space… RAM

You have too many applications open so need to close down some of these to free up RAM
Delete photos at you peril i.e. The other answer is wrong