When soft, a penis is usually between 6 and 13 centimetres long. An erect one is usually somewhere between 7 and 17 centimetres long. The average is about 12 centimetres. Smaller penises grow more in size when they become erect compared to large penises.
Some boys joke a lot about the size of their penis or other people's penises. It’s often because they feel insecure, or because they want to look tough, or they want to make up for lack of knowledge.
If you want to measure your penis, do it when it’s erect, on the top side – the side closest to your belly.