How do I convert a file to Base64?

Choose Encode, then drop a file on the box or click it to pick one of up to 5 MB. Choose Plain Base64 String or Data URI, then Copy or Download Base64, which saves photo.png as photo.png.base64.txt. The file is read in your browser and is not uploaded.

How do I convert Base64 back to a file?

Choose Decode, paste the Base64 or the whole data URI, optionally type a file name, and press Decode. The page shows the byte count and, for text, the content; Download saves the file under the name shown on the button, and binary results can also be copied back as standard Base64.

How much larger is Base64 than the file?

About a third: characters = 4 × ceil(bytes ÷ 3). A 5 MB file (5,242,880 bytes) becomes 6,990,508 characters, and a data URI adds its data: ;base64, header in front.

Does it decode URL-safe Base64 and missing padding?

Yes. The URL-safe - and _ (as in JWT segments) are read, as long as they are not mixed with + and /, and the = padding may be left off: SGVsbG8gV29ybGQ decodes to the 11 bytes of Hello World. White space and line breaks are ignored.

How does it know the file type?

From the data URI type when there is one (text/plain gives .txt), otherwise from the first bytes: PNG, JPEG, GIF, WebP, PDF, ZIP and GZIP are recognised. Anything else is saved as .bin unless you type a name with its own extension. A result found to be PNG, JPEG, GIF or WebP from its first bytes, or BMP, ICO or SVG from its data URI type, is also shown as an image.

Can a link fill in the Base64 to decode?

Yes: the q parameter fills the Base64 box, mode chooses Encode or Decode, and filename fills the download name. A link only fills the fields; nothing is decoded or downloaded until you click.

Base64 File to String

Encode a file of up to 5 MB to Base64 or a data URI, or decode Base64 back to a downloadable file named from its data URI type or first bytes. How it works

Output Format

About the Base64 File to String

Base64 writes every 3 bytes as 4 characters, so the text is about a third larger than the file: the 3 bytes of Man are TWFu. The tool encodes a file of up to 5 MB to plain Base64 or a data URI, and decodes pasted Base64 or a data URI back to a file you can download, shown as text when it is valid UTF-8.

Decoding examples

Pasted	Result	Download name
TWFu	3 bytes, text: Man	decoded.bin
SGVsbG8gV29ybGQ	11 bytes, text: Hello World	decoded.bin
data:text/plain;base64,SGVsbG8gV29ybGQ=	11 bytes, text: Hello World	decoded.txt
iVBORw0KGgo=	8 bytes, binary	decoded.png
-_8=	2 bytes, binary, URL-safe alphabet	decoded.bin
+_8=	Error: the text mixes the standard (+ /) and URL-safe (- _) alphabets	(none)
=	Error: the text holds only padding (=), no data	(none)

With the file name field empty. iVBORw0KGgo= is the 8-byte PNG signature, so the extension comes from the first bytes; the data URI gives text/plain, so .txt.

Download names for a decoded PNG

Name typed	Saved as
(empty)	decoded.png
photo	photo.png
report.pdf	report.pdf
a/b:c*?.txt	a_b_c__.txt
...hidden	hidden.png

Slashes and characters Windows refuses become _, leading dots go, and a name without an extension gets the one found for the file. Names are cut to 100 characters.

Frequently asked questions

How do I convert a file to Base64?: Choose Encode, then drop a file on the box or click it to pick one of up to 5 MB. Choose Plain Base64 String or Data URI, then Copy or Download Base64, which saves photo.png as photo.png.base64.txt. The file is read in your browser and is not uploaded.
How do I convert Base64 back to a file?: Choose Decode, paste the Base64 or the whole data URI, optionally type a file name, and press Decode. The page shows the byte count and, for text, the content; Download saves the file under the name shown on the button, and binary results can also be copied back as standard Base64.
How much larger is Base64 than the file?: About a third: characters = 4 × ceil(bytes ÷ 3). A 5 MB file (5,242,880 bytes) becomes 6,990,508 characters, and a data URI adds its data:<type>;base64, header in front.
Does it decode URL-safe Base64 and missing padding?: Yes. The URL-safe - and _ (as in JWT segments) are read, as long as they are not mixed with + and /, and the = padding may be left off: SGVsbG8gV29ybGQ decodes to the 11 bytes of Hello World. White space and line breaks are ignored.
How does it know the file type?: From the data URI type when there is one (text/plain gives .txt), otherwise from the first bytes: PNG, JPEG, GIF, WebP, PDF, ZIP and GZIP are recognised. Anything else is saved as .bin unless you type a name with its own extension. A result found to be PNG, JPEG, GIF or WebP from its first bytes, or BMP, ICO or SVG from its data URI type, is also shown as an image.
Can a link fill in the Base64 to decode?: Yes: the q parameter fills the Base64 box, mode chooses Encode or Decode, and filename fills the download name. A link only fills the fields; nothing is decoded or downloaded until you click.

Data URIs, API payloads and blobs from logs

Turn a small icon, font or PDF into a data URI to paste into CSS, HTML, JSON or an email template; the data URI uses the file type your browser reports for the file, or application/octet-stream when it reports none. Fill a Base64 field when testing an API that takes file contents, and go the other way with a Base64 blob from a log, an API response or a JWT segment: paste it and download the file it holds. A PNG, JPEG, GIF, WebP, BMP, ICO or SVG image is previewed on the page, whether you chose the file or decoded it. Keep data URIs for small files, since the text is a third larger than the file. The file is read in your browser and is not uploaded.

How the encoding works

Base64 writes every 3 bytes as 4 characters from A-Z a-z 0-9 + / and pads the end with =, so the text is about a third larger than the file: characters = 4 × ceil(bytes ÷ 3). The browser's own encoder reads the file, and the data URI format adds data:<type>;base64, in front. Decoding ignores white space, accepts missing padding and the URL-safe - and _ (not mixed with + and /), and shows the result as text only when every byte is valid UTF-8 without control characters.

Example: TWFu decodes to the 3 bytes of Man, and the unpadded SGVsbG8gV29ybGQ to the 11 bytes of Hello World. The download is named decoded.<ext>, with the extension from the data URI type or the first bytes (PNG, JPEG, GIF, WebP, PDF, ZIP, GZIP), else bin. Limit: 5 MB decoded, which is 6,990,508 Base64 characters.

Related Tools

View all tools

Dev

SVG to CSS Background Converter

Convert SVG markup to a CSS background-image data URI, URL-encoded or Base64. Adds a missing xmlns, rejects non-SVG input, gives url() or inline-style output.

Conversion

Hex to ASCII

Convert hex to ASCII text: 48 65 6C 6C 6F is Hello. Bytes are read as UTF-8, and odd digit counts or bad characters get an error.

Dev

Base64 Converter

Encode text to Base64 or decode Base64 to text. UTF-8, standard and URL-safe alphabets, optional padding on decode, up to 250,000 characters.

Dev

Chmod Calculator

Type a chmod mode such as 755 or 4755 to see rwxr-xr-x, or paste rwxr-xr-x or tick read, write and execute for owner, group and public to get the octal number.

Dev

Hash Generator

Compute the MD5, SHA-1, SHA-256, SHA-384 or SHA-512 hash of text or a file and compare it with an expected checksum. The file is hashed in your browser.

Dev

HTML Entity Encoder

Encode text to HTML entities (& < > " ') or decode any of the 2,231 named references in the HTML standard and numeric ones such as é.