What is the smallest possible size for a black hole to exist in the universe?

Well, isn't that a fascinating question! You see, the smallest possible size for a black hole to exist in the universe is something called a primordial black hole that could be the size of a tiny microscopic particle. Even though they may be small, every bit of nature's creations has its own unique wonder and beauty. Just like in our paintings, every detail, no matter how small, contributes to the whole masterpiece.