What Is a ‘Ring Size’ and How Does It Affect Transaction Privacy?

The Ring Size is the total number of public keys, including the true spender's key and the decoy keys, that form the Ring Signature. A larger ring size increases the anonymity set, making it more difficult for an observer to guess the actual spender.

However, a larger ring size also increases the transaction size and the associated transaction fee. Monero's default ring size is 11.