Decimal to Base64 Converter

Encode a decimal byte array (0-255 per value) to a Base64 string.

Decimal bytes (comma, space, or newline separated)

13 bytes parsed

Base64 output

SGVsbG8sIFdvcmxkIQ==

How decimal-to-Base64 conversion works

Base64 encodes raw bytes as printable ASCII text using 64 characters (A–Z, a–z, 0–9, + and /), padded with = to a multiple of 4 characters. Each group of 3 input bytes becomes 4 Base64 characters, which is why encoded output is roughly 33% larger than the original data.

This tool treats each number you enter as one byte (0-255), builds the raw byte sequence, then Base64-encodes it. For example, the decimal bytes 72, 101, 108, 108, 111 (the ASCII codes for "Hello") encode to SGVsbG8=. All conversion happens locally in your browser — nothing is uploaded anywhere.

Built and maintained by Meet Shah · Last updated 1 August 2026

What this tool is used for

Encoding a byte array from a protocol trace into Base64 for a text field.
Producing a Base64 value from raw byte values you have as numbers.
Checking that your own byte-to-Base64 conversion matches a reference.
Building a test fixture from explicit byte values.
Converting a decimal byte dump into a compact transportable form.

Frequently Asked Questions

What input does it expect?: A list of byte values, 0–255, separated by commas, spaces or newlines. Each token must be a non-negative integer in that range; anything above 255 is not a byte and is reported as an error rather than truncated, because masking off the high bits would corrupt the output invisibly.
How does the encoding work?: The bytes are assembled into a binary string — one character per byte, char code 0–255 — and passed to `btoa`. That is the browser's native path for encoding raw bytes, and the reference case is checkable: [72,101,108,108,111,44,32,87,111,114,108,100,33] gives `SGVsbG8sIFdvcmxkIQ==`.
Why does the output end in equals signs?: Padding. Base64 packs three bytes into four characters, so an input length that is not a multiple of three leaves a partial group — one `=` for two leftover bytes, two for one. Thirteen bytes is four groups plus one, hence the `==` on the Hello, World example.
How much does Base64 inflate the data?: By exactly a third: four output characters per three input bytes, so 33% before padding. That is the cost of making binary safe for a text channel, and it is why inlining a large image as a data URI is usually a worse trade than one extra request for it.
Is Base64 a form of encryption?: No, and treating it as one is a recurring security mistake. It is a reversible encoding with no key — anyone can decode it instantly. It exists to move bytes through systems that only handle text, not to hide anything from anyone.

Common errors and gotchas

Including values above 255, which are not bytes and cannot be encoded as such.
Mixing separators so the byte boundaries become ambiguous.
Assuming the decimal values are characters rather than bytes, which differ for anything non-ASCII.
Expecting the output to be shorter than the input, when Base64 always grows the underlying bytes by a third.
Confusing standard Base64 with the URL-safe variant when the destination requires one specifically.