About 33% larger. Every 3 input bytes become 4 output characters. So a 1MB binary blob becomes ~1.33MB Base64. Plus padding characters (=) at the end when the input length isn’t a multiple of 3. This overhead matters for large payloads (image data, file uploads, PDF blobs). Alternatives: transmit as raw binary using multipart/form-data or application/octet-stream — HTTP handles binary natively. Use Base64 only when the transport is text-only (JSON, email, JWT). Test size delta with the Base64 converter.
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What Is a JWT?
JWT (JSON Web Token) is the dominant format for API authentication, OAuth access tokens, and stateless session management. Three base64-encoded segments carry the header, claims, and signature — anyone can read them, but only the key holder can produce a valid token.