Number base converter

What this base converter does

Enter a non-negative integer in binary, octal, decimal or hexadecimal and read the same value in all four bases at once. Each digit is validated against the selected base before conversion, so a 2 in a binary field or a g in a hex field is reported as an error instead of being silently truncated the way parseInt would. Values up to 2^53 − 1 are supported exactly; everything runs in your browser.

How to use it

1. Choose the Input base — Binary (2), Octal (8), Decimal (10) or Hex (16).
2. Type the number without a prefix (no 0x, 0b, #).
3. The BIN / OCT / DEC / HEX rows update as you type; hex output is lowercase.
4. Click Copy next to the row you need.

Worked examples

Decimal	Binary	Octal	Hex	Why you meet it
10	1010	12	a	First hex letter
127	1111111	177	7f	Largest signed 8-bit value; 127.0.0.1
255	11111111	377	ff	One full byte; max RGB channel
493	111101101	755	1ed	chmod 755
1000	1111101000	1750	3e8	1 ms in µs
1024	10000000000	2000	400	1 KiB
65535	1111111111111111	177777	ffff	Max port number, 16-bit max
4294967295	32 ones	37777777777	ffffffff	32-bit unsigned max

Converting by hand works on the same idea in every base: repeatedly divide by the base and read the remainders backwards. 255 ÷ 16 = 15 remainder 15 (f), 15 ÷ 16 = 0 remainder 15 (f), so 255 = ff.

Bit tricks worth memorizing

Hex ↔ binary is a lookup, not a calculation. Each hex digit maps to a 4-bit group (a nibble): 3e8 = 0011 1110 1000. Pad the binary number to a multiple of 4 on the left and translate group by group. Octal works the same way with 3-bit groups: 755 = 111 101 101.

Powers of two have a single 1 bit. 1024 = 10000000000 (a 1 followed by ten zeros), so n & (n - 1) === 0 is the classic power-of-two test.

Masks. 0xff keeps the low byte, 0xffff the low two bytes. To pull the green channel out of 0x1e90ff: shift right by 8 and mask, (0x1e90ff >> 8) & 0xff = 0x90 = 144.

Permissions. Each octal digit is rwx as 4+2+1. 7 = 111 = rwx, 5 = 101 = r-x, 4 = 100 = r—, 6 = 110 = rw-. So 644 is rw-r--r--.

Reading a hex dump. Two hex characters per byte; 48 65 6c 6c 6f is Hello in ASCII, because 0x48 = 72 = H.

Doing it in JavaScript

parseInt('ff', 16);        // 255   — parse from a base
(255).toString(2);         // '11111111' — format to a base
(255).toString(16).padStart(4, '0'); // '00ff'
0b1010 + 0o17 + 0xff;      // literals: 10 + 15 + 255 = 280
Number('0x1f');            // 31 — Number() understands prefixes, parseInt(…, 16) does not need them

Two things catch people out. parseInt('12', 2) returns 1, not an error — it stops at the first invalid digit, which is why this tool validates the whole string first. And numbers above Number.MAX_SAFE_INTEGER need BigInt: BigInt('0xffffffffffffffff').toString(2) works, while the plain Number version rounds.

Bitwise operators (&, |, >>, ~) in JavaScript work on 32-bit signed integers, so 0xffffffff | 0 is -1 and 1 << 31 is negative. Use >>> 0 to read the result as unsigned, or BigInt for 64-bit work.

Related tools and snippets

• Color converter — a hex color is just three bytes; convert #1e90ff to rgb(30, 144, 255) and other spaces.
• Hash generator — digests are long hex strings; see how many bits 64 hex characters represent.
• UUID generator — 32 hex digits = 128 bits, grouped 8-4-4-4-12.
• CSS unit converter — a different kind of conversion: px, rem, em and viewport units.
• Timestamp converter — Unix timestamps are often shown in hex in logs and packet captures.