What is the space overhead of Base64 encoding?

The trick behind base64 encoding is that we use 64 different ASCII characters including all letters, upper and lower case, and all numbers. Base64 is apparently wasteful because we use just 64 different values per byte, whereas a byte can represent 256 different characters. Faster Base64 Encoding and Decoding using AVX2 Instructions, ACM Transactions on the Web 12 (3), 2018.

Source: lemire.me