Convert decimal numbers into binary, grouped in fours
Runs in your browser. Nothing you type is sent anywhere. Updated on 24 Oct 2026.Enter a decimal number and see it in binary, grouped in blocks of four bits so it is easy to read and copy. Negative numbers show their two's complement pattern at 8, 16, 32 or 64 bits, which is how a computer actually stores them: -5 in 8 bits is 1111 1011. Hex and octal appear alongside.
The page opens with an example in the Decimal row; type your number over it.
Read the Binary row, grouped in fours while Group digits is on.
For a negative number, choose 8-bit, 16-bit, 32-bit or 64-bit under Two's complement and read Bits.
Press the copy icon beside Binary to copy the digits without the grouping spaces.
This number base converter turns an integer from any base between 2 and 36 into binary, octal, decimal, hexadecimal and a base of your choice at the same time. Type into any row and the others follow, grouped for reading: binary and hex in fours, decimal with thousands separators.
Programmers use it to read a hex error code or memory address as a number, to write a bit mask in binary, to decode a base 36 short ID, or to see what a register value means as a signed integer. Students use it to check base conversion homework and to understand two's complement, the way computers store negative numbers.
All arithmetic uses JavaScript BigInt, so a 40-digit decimal or a 128-bit hex value converts exactly, with no rounding at 2 to the power 53 as ordinary numbers have. Input can include 0b, 0o or 0x prefixes, a minus sign, and spaces, underscores or commas between groups. Only whole numbers are converted; fractions are refused with a message. Nothing leaves your browser.
The rest of the article, and all 6 questions about Number Base Converter, are on the Number Base Converter page.
Multiply each bit by the power of two for its position, counting from 0 on the right, and add the results. 1011 is 1x8 + 0x4 + 1x2 + 1x1, which is 11. Or type the binary number into the Binary row here and read the Decimal row; spaces between groups of bits are fine.
Each hex digit is worth 16 times the digit to its right, with A to F meaning 10 to 15. 0x1F is 1x16 + 15, which is 31. Paste the value, with or without 0x, into the Hexadecimal row and the decimal value appears, exact even for values far longer than 16 digits.
Ordinary JavaScript numbers are floating point and lose precision above 9,007,199,254,740,991 (2 to the power 53, minus 1), so the last digits of a large hex or decimal value get rounded. This tool uses BigInt, which keeps every digit exact at any length up to 4,096 characters.
No, only whole numbers. Fractional values do not convert cleanly between bases, because a short decimal such as 0.1 becomes an endless repeating binary fraction. The tool says so rather than guessing. For floating-point bit patterns, a dedicated IEEE 754 tool is the right choice.
Still stuck? Ask about Number Base Converter and anybody who knows can answer. No account needed.
On the related tools: Base58 Encoder and Decoder – Encode text or hex bytes to Base58 with the Bitcoin alphabet, or decode Base58 back · TSV to JSON – Convert tab-separated values, such as a paste from Excel, into JSON.
In the collection Developer Converters.