Decimal to Binary
Convert decimal numbers to binary in your browser. Optional 0b prefix, zero-padding to a fixed width, and grouping every 4 or 8 bits for readability.
Decimal in, binary out
Each decimal number is emitted as a base-2 string, with optional zero padding to a fixed width.
10 15 42
1010 1111 101010
What you'll use this for
Anywhere you need to see the underlying bits of a decimal value — bitmasks, debugging, hardware specs.
Bit twiddling
Inspect the on/off pattern of a decimal value to spot a bad flag.
CS homework
Verify base-10 to base-2 conversions for assignments and study.
Bitmask design
Design bitmasks by writing the decimal value and reading the bit pattern.
Hardware
Encode register values and protocol fields with exact bit widths.
How to convert decimal to binary
Paste decimal numbers
One per line or separated by spaces or commas. Negative values are skipped.
Pick width and grouping
Pad to 4 / 8 / 16 / 32 bits, group bits for readability, and optionally prefix with 0b.
Click Convert
Or leave auto-convert on for live updates. Runs entirely in your browser.
Copy the result
Copy to clipboard or download as .txt. Round-trip with the reverse tool if you need to verify.
Frequently asked questions
53 bits (the JS safe-integer limit). Negative numbers are skipped.
Yes — use the Pad width option (4 / 8 / 16 / 32 bits).
Yes.
Newlines, spaces, or commas — any combination.
Yes — use Binary to Decimal.
About this converter
This tool converts numbers from base 10 (decimal) to base 2 (binary). Internally it calls n.toString(2), then optionally zero-pads the result to a fixed bit-width and groups bits for readability.
How conversion works
- Input is split on whitespace and commas into individual decimal tokens.
- Each token is parsed with
parseInt(token, 10)— negatives are skipped. - The bit-string is left-padded with zeros up to the requested width, then optionally split into groups.
Why pad?
- Fixed bit-width matters when bits represent a register, a flag set, or a protocol field.
- Grouping by 4 or 8 bits makes long bitstrings easier to read at a glance.
- 0b prefix matches the syntax used by JS, Python, and Rust for binary literals.