How long is a O katana?

I'm curious, how long exactly is a traditional O katana sword? It's a well-known fact that the O katana is a revered and iconic weapon in Japanese culture, renowned for its sharpness, durability, and beauty. But I've always wondered about the specific dimensions of this iconic blade. Could you enlighten me on the typical length of an O katana, and perhaps even provide some insight into why this length was chosen?