Count One Bits

The Hamming weight of a binary number is the number of 1-bits it contains. Also called population count (popcount) – it’s a primitive operation in many CPUs (the POPCNT instruction). Used in cryptography, error correction, bitset operations, and combinatorial math.

Priority order: 0b... prefix → binary; 0x... prefix → hex; all 0/1 digits → binary; contains a-f → hex; all 0-9 → decimal. Ambiguous strings (e.g., 10 – binary 2 or decimal 10?) get treated as binary. Use explicit format selector or 0x/0b prefixes to disambiguate.

Natural width counts only the bits actually present (e.g., 0b1010 = 4 bits). Fixed widths pad with leading zeros: 0b1010 at 8-bit = 00001010, still 2 ones but now 6 zeros. The 1s count never changes – only the 0s count and percentage do.

Indices where 1-bits sit, counted from the LSB (least significant bit) = position 0. 0b1010 has 1s at positions 1 and 3. Useful for bitmasks, set-theoretic operations, finding which flags are set.

JavaScript’s BigInt handles arbitrary precision, so practically unlimited – limited only by browser memory. A 1000-character binary string parses fine.

Binary input 0001010 has natural width 7 (the leading zeros count toward total bits). Hex 0F has natural width 8 (2 hex chars × 4). Decimal natural width is the minimum bits needed.

Not directly supported as -N. For two’s-complement bit patterns, convert to the appropriate hex or binary form first (e.g., -1 as 8-bit signed = 0xFF).

Lines that don’t match any format (e.g., FFG, five, 3.14) error individually without stopping the batch. The error count appears in stats, and individual error positions show in the status line.

No. Everything runs in your browser with JavaScript – nothing is sent to a server, logged, or stored, and the tool keeps working offline once the page has loaded.

500 rendered in the table to keep the page responsive. The TSV download includes all rows.