Base64 Encoding: What It Is and When to Use It

Base64 is a binary-to-text encoding scheme that represents binary data in ASCII string format. It is used extensively in web development for embedding data, email attachments, and API communication.

How Base64 Works

Base64 converts every 3 bytes of binary data into 4 ASCII characters using a set of 64 characters (A-Z, a-z, 0-9, +, /). If the input length is not divisible by 3, padding characters (=) are added.

Common Uses in Web Development

Data URIs embed small images or fonts directly in HTML and CSS. API authentication often uses Base64 for HTTP Basic Auth headers. Email attachments are Base64 encoded per the MIME standard. JSON payloads sometimes include Base64 encoded binary data.

URL-Safe Base64

Standard Base64 uses + and / which have special meaning in URLs. URL-safe Base64 replaces these with - and _ respectively. This variant is used in JWTs and many web APIs.

Size Considerations

Base64 encoding increases data size by approximately 33%. A 3 KB image becomes about 4 KB when Base64 encoded. This overhead means Base64 is best for small data. For larger files, direct binary transfer is more efficient.

In Practice

Use our Base64 Encode/Decode tool to quickly convert between formats. For images, Base64 is useful for small icons and sprites under 2-3 KB. For API development, Base64 is essential for handling binary data in JSON payloads.