There is no definitive answer to this question as it is subjective. However, we can look at some of the largest heads in the world and try to come to a conclusion.
The largest head in the world belongs to the statue of Buddha Vairocana in China. The statue is over 120 feet tall and its head alone is almost 60 feet wide. This makes it the largest Buddha statue in the world and also one of the largest statues of any kind.
Another contender for the title of biggest head in the world is Mount Rushmore National Monument in South Dakota, USA. The monument features four giant sculptures of former US presidents; George Washington, Thomas Jefferson, Theodore Roosevelt and Abraham Lincoln. Each sculpture has a height of 60 feet and a width of 27 feet, making them some of the largest sculptures ever created.
So which is it? The Buddha Vairocana statue or Mount Rushmore National Monument? It's hard to say for sure but both are definitely contenders for the title of biggest head in the world.