What Base64 Actually Is

What exactly IS Base64? Base64 is an encoding system; it’s used to take binary data - which in this case is represented by the bytes that make up an image file - and translate it into an ASCII character set that’s safe to include in text-based documents like HTML, CSS, and JSON. Base64 uses a set of 64 characters: all uppercase English alphabet letters (A-Z), all lowercase English alphabet letters (a-z), all numerals (0-9) and both + and / characters. All the bits and bytes in any given 3-byte unit are turned into a 4-character set - that’s why the Base64 encoded file is around 33% larger than the original file.

What looks like garbage in this example actually contains all the data needed to recreate the entire image.

A data URI, normally starts like “data:image/png;base64,” and then the rest of that gibberish in the preceding section. The browser reads the entire data URI - decode it and render the image as if it were loading a standard, external image file - and this all without requesting any additional information from the web server. And THIS is why you should generally prefer a data URI to linking to a standard image file.

How Base64 Encoding Works for Images

When we have an image file in the form of base64 it converts every bit of the image file to a specific 6 bits character, then gets converted into a of the 64 specific characters. After doing this for all the bits in the image file, the output would be a huge long string containing the whole image’s information. This long string is typically prefaced with a dataURI (Data:image/png:base64:,) to notify the browser on what kind of file it is and how it was encrypted, etc. When the output is processed by the browser, it gets decodes immediately and shows up as a normal image. Though the size increases by 30-37%, in situations where it is far more critical to reduce http requests than the size of a file, Base64 comes to rescue.

Where This Genuinely Helps

Small icons, the simple logo, the tiny little graphic which gets repeated over and over on a page - these can be embedded via Base64, thus saving one network request per image. On a page containing a multitude of tiny graphic elements, this can add up: every one would otherwise have to be downloaded in its own round-trip request to a server. A page loading twenty icons means twenty requests to the server, each with its own connection overhead, HTTP headers, and connection latency. Embedding via Base64 avoids this entirely and, depending on connection speeds, could result in a substantial improvement in page loading speed where each round-trip adds an noticeable latency penalty. The file-size increases of Base64 encoding of very small files are not substantial; 2KB of an image may increase to about 2.7KB if base64 encoded. It is not much in terms of total file size of the overall page. This approach of avoiding round-trip requests can save several hundred milliseconds on a slow connection.

Where It Stops Making Sense

A Base64 string runs roughly a third larger than the original binary file it's encoding, because of how the encoding scheme works at a byte level. Encoding a large photo this way bloats your actual HTML or CSS file itself rather than letting the browser fetch and cache the image on its own, separately, the way it normally would with a regular image reference — and that cached version can be reused across page loads and even across different pages, which a Base64 string baked directly into your markup cannot. This is the fundamental tradeoff: Base64 eliminates a network request at the cost of a larger file and no browser caching. For small images where the size difference is negligible, the eliminated request wins.A separate image file referenced from the CSS can be cached independently, so subsequent page loads only need to fetch the CSS file, not the image again.A separate image file is just a file — you replace it, the change takes effect on the next page load, and the old cached version gets invalidated when the filename or path changes.

Supported Formats

The tool works for JPG, PNG, GIF, SVG, and WebP images. The result provides the correct MIME type prefix – data:image/jpeg for JPG images, data:image/png for PNG images, and so forth – so that your browser will know how to decode the data properly. It even handles SVGs; SVGs as Base64 do shed a few benefits of SVGs, though - such as applying CSS to separate parts or working with them through Javascript.

Privacy

Everything runs in your browser. The image you upload never leaves your machine — the encoding happens entirely client-side using JavaScript and the browser's canvas API. There's no server processing, no upload, no storage. The encoded string is generated locally and displayed in your browser for you to copy. If the image contains sensitive content — personal photos, client work, unreleased designs — it stays on your device throughout the entire process.