Base45 converter

Base45 is an encoding defined in RFC 9285 that turns binary data into the 45 characters supported by the alphanumeric mode of QR codes: digits 0 to 9, uppercase A to Z, space and the symbols $ % * + - . / :. Because QR alphanumeric mode stores characters more densely than byte mode, Base45 produces smaller QR codes than Base64 for the same data.

How to use it

1. Paste text to encode it into Base45, or paste a Base45 string to decode it.
2. Copy the output.

How the encoding works

Input bytes are processed in pairs. Each pair is read as a 16-bit number n = a × 256 + b and written as three Base45 digits c, d, e such that n = c + d × 45 + e × 45². A trailing single byte becomes two characters. The result is roughly 1.5 characters per byte.

Example

The text AB is bytes 65 and 66, so n = 65 × 256 + 66 = 16706. Dividing: 16706 = 11 + 45 × 11 + 2025 × 8, giving digits 11, 11, 8, which map to BB8. Decoding BB8 reverses the steps and returns AB.

Where you will see Base45

• EU Digital COVID Certificates: the QR payload starts with HC1: followed by Base45 data, which is zlib-compressed CBOR/COSE.
• Other signed health and travel credentials that follow the same pattern.
• Any application that needs compact binary data inside a QR code.

Decoding a health certificate here only reveals the compressed binary payload; it must still be decompressed and parsed as CBOR to read the fields.