1. What Is utf8 In theory, utf8 uses 1-6 characters, In practice, the latest utf8 specification uses only one to four bytes, and can encode at most 21 bits, which is exactly enough to represent all 17 Unicode planes. 2. What Is utf8mb4 utf8mb4 is a superset of utf8. In theory, if you were using utf8 before and then change the charset to utf8mb4, it will not cause any problem when reading the existing utf8-encoded data.