Number Base Converter

Number Converter gathers the jobs people usually need four different sites for. Type a number in binary, octal, decimal, hexadecimal or any base from 2 to 36, and every other base fills in as you type. Numbers are handled as exact big integers, so a 40-digit hex key converts without the rounding errors that make ordinary calculators give up past about 16 digits.

It also shows how the number sits in memory as an 8, 16, 32 or 64-bit integer using two’s complement, the system computers use for negative numbers, and what the same bits mean when read as signed or unsigned. The Text ↔ bytes tab turns any text into UTF-8 bytes in binary, hex, decimal or octal and back again, with a character-by-character table that shows why an emoji takes four bytes.

Roman numerals work both ways from 1 to 3,999,999, using the bar over a letter for thousands, and invalid numerals such as IIII or IC are caught with the correct form suggested. Number to words writes 1,234 as “one thousand two hundred thirty-four”, with British “and”, Indian lakh and crore, ordinals and money in eight currencies.

1. Pick a tab: “Number bases”, “Roman numerals”, “Text ↔ bytes” or “Number to words”.
2. In Number bases, type in any box. Use the “Base” menu on the last row for bases such as 3, 12 or 36.
3. Tick or untick “Group digits” and “Capital A–F” to change how results look, then press the copy button beside a row to copy it without spaces.
4. In Roman numerals, type a number on the left or a numeral on the right. If a numeral isn’t standard, press the “Did you mean…” button to fix it.
5. In Text ↔ bytes, type in either box and choose Binary, Hex, Decimal or Octal. In Number to words, set “Counting”, “Capitals” and “Currency”, then press “Copy” on the result you want.

• Binary, octal, decimal and hex side by side, plus any base from 2 to 36, exact at any length.
• Accepts 0x, 0b and 0o prefixes, minus signs, spaces and underscores.
• Two’s-complement table for 8, 16, 32 and 64 bits, showing whether the number fits and its signed and unsigned readings.
• Roman numerals from 1 to 3,999,999 in both directions, with a part-by-part breakdown, bar notation and a bracket form for plain text.
• Strict Roman numeral checking that explains the mistake and offers the standard spelling.
• Text to UTF-8 bytes and back in binary, hex, decimal or octal, safe for accents, all scripts and emoji.
• Number to words with British “and”, international or Indian counting, decimals, negatives and ordinals.
• Money in words and cheque style (“and 56/100”) for pounds, dollars, euros, rupees, rand and more, with optional “only”.

• Decimal bytes need a separator, because 72105 could be 72 105 or 7 21 05, so spaces are added if you choose “Nothing”.
• To read a hex colour such as #7CC4FF, convert it two digits at a time: 7C is 124, C4 is 196 and FF is 255.
• If bytes won’t turn back into text, a multi-byte character has probably been cut in half. Check that every emoji has all four of its bytes.
• For a cheque, choose your currency and tick “End with only”. Write the figure exactly as shown and fill any gap so nothing can be added.