Number Base Converter

What this does

Converts numbers between bases — binary (2), octal (8), decimal (10), hexadecimal (16), and any custom base from 2 through 36. Edit any field and the others update live.

Built on JavaScript BigInt so very large numbers convert without precision loss. parseInt(x, 16) runs out of precision around 2⁵³; this tool handles values into the thousands of digits.

Prefixes accepted

• Binary input may start with 0b (0b1010 = 10).
• Octal input may start with 0o (0o777 = 511).
• Hex input may start with 0x (0xFF = 255).
• All bases accept negative values with leading -.

Output is plain digits (no prefix) — copy-paste into your code with whatever prefix your language wants.

Common conversions you’ll need

When you actually use this

• Reading hex dumps. A debugger shows 0x7FE3 — what bit pattern is that? Convert to binary.
• Setting register bits. “Bit 5 of register 0xFF22 should be 1.” Decimal 32 in binary 100000 shows you the bit position.
• CSS color RGB ↔ hex. rgb(124, 58, 237) → #7C3AED. Three decimal-to-hex conversions.
• File mode bits. chmod 755 in octal is rwxr-xr-x; the binary 111101101 shows which permission bits are set. (For chmod specifically, see our chmod calculator .)
• Subnet math. /24 netmask is 255.255.255.0 — the binary 11111111…0 makes the prefix length obvious.
• Base-36 short IDs. Encoding a numeric ID in base 36 gives compact alphanumeric IDs (xkcd1 → 1610393). Useful for URL shorteners.
• Reading ASCII codes. 'A' is 65 decimal, 0x41 hex, 0b01000001 binary.

Bases above 16

Bases 17 through 36 use letters g–z for digit values 16–35. Common cases:

• Base 32 — without confusing characters (no I, L, O, U). Used by Crockford’s base32, ULIDs.
• Base 36 — 0–9 + a–z. Compact alphanumeric IDs without case sensitivity. Doubles down: a 64-bit number fits in 13 base-36 chars (vs 16 hex chars).
• Base 62 — would add uppercase but JavaScript Number.toString(62) doesn’t support it natively. Beyond what this tool does (we cap at 36).

What this does NOT do

• Floating-point conversion. This tool is for integers only. Hex floats (0x1.8p+1) and IEEE 754 inspection need a different tool.
• Two’s complement / signed binary representation. Negative inputs use - prefix on positive magnitude. To see the actual bit pattern of a negative int32, that’s a different conversion (we’d need a fixed bit-width input).
• Arbitrary-precision floats. BigInt is integer-only.

Privacy

Runs entirely in your browser. Your numbers stay local.

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