Geography and oceanography are full of terms that most people recognise, but are very difficult when it comes to actually defining them. Oceanography in particular has words like ocean, sea, gulfs and bays, and most people think that they know the difference, but there is actually a great deal of confusion about the difference between a gulf and a bay.
Most people normally say that the main difference between a gulf and a bay actually comes down to size, with a gulf being the larger of the two, in just the same way as an ocean is larger than a sea. It initially seems like a good theory, after all the Gulf of Mexico is the tenth largest body of water on the planet. Then of course it will be pointed out that the Bay of Bengal is larger. In most measurements, the Gulf of Mexico is 1.6 million square kilometres, with the Bay of Bengal coming in at 2.17 million square kilometres. Indeed there are many small gulfs, including the gulfs of California and the Gulf of Newfoundland.
Bay though is a difficult description when it comes to small bays. Many small coastal bays, could be described as coves rather than bays, but there is often a historical name attached.
If size is not the most important consideration therefore when it comes to the difference between a gulf and bay, then it is normally a question of looking at the physical characteristics of the bodies of water.
Gulfs are normally bodies of water that are surrounded by land with a narrow entrance through a strait. The entrance to the Gulf of Mexico may not look that narrow, but compared to the widest point of the gulf it is, and the entrance to the gulf is often named as the Straits of Florida.
A Bay on the other hand is normally described as a body of water that is not as enclosed, and has therefore got a much wider mouth compared to a strait.
Again though, a description of the body of water is not always enough to distinguish between a gulf and a bay. After all the Mediterranean Sea could equally be called the Gulf of the Mediterranean based purely on description. Names are misleading and the name given to a body of water may differ between who is talking about it, a prime example is the Bay of Biscay, and although widely known as a bay is actually called the Golfe de Gascogne in French.