Decimal to Binary Converter
Convert a decimal (base 10) number to binary (base 2) instantly. As an example, 255 = 11111111. It runs entirely in your browser.
| Base | This number |
|---|---|
| Binary (base 2) | — |
| Octal (base 8) | — |
| Decimal (base 10) | — |
| Hexadecimal (base 16) | — |
How to convert decimal to binary
To convert a decimal number to binary, divide it by 2 repeatedly and read the remainders from last to first. For example, 255 in binary is:
255 (decimal) = 11111111 (binary)
Worked example: 255 in binary
Reading 255 as base 10: 2 × 102 (= 200) + 5 × 101 (= 50) + 5 × 100 (= 5) = 255 in decimal, which is 11111111 in binary.
Binary, octal, decimal & hexadecimal reference table
| Decimal | Binary | Octal | Hex |
|---|---|---|---|
| 1 | 1 | 1 | 1 |
| 2 | 10 | 2 | 2 |
| 4 | 100 | 4 | 4 |
| 8 | 1000 | 10 | 8 |
| 10 | 1010 | 12 | A |
| 15 | 1111 | 17 | F |
| 16 | 10000 | 20 | 10 |
| 32 | 100000 | 40 | 20 |
| 64 | 1000000 | 100 | 40 |
| 100 | 1100100 | 144 | 64 |
| 128 | 10000000 | 200 | 80 |
| 255 | 11111111 | 377 | FF |
| 256 | 100000000 | 400 | 100 |
| 1024 | 10000000000 | 2000 | 400 |
About decimal and binary
Decimal: Decimal is base-10, the everyday number system using digits 0–9.
Binary: Binary is base-2: every digit (bit) is 0 or 1. It is how computers store and process all data at the hardware level.
Frequently asked questions
- What is 255 decimal in binary?
- 255 in decimal (base 10) equals 11111111 in binary (base 2), which is 255 in decimal.
- How do I convert decimal to binary by hand?
- Repeatedly divide the decimal number by 2 and read the remainders from last to first. 255 in base 2 is 11111111.
- Is this exact for very large numbers?
- Yes. The converter uses big-integer (BigInt) arithmetic in your browser, so even very long decimal values convert to binary with no rounding or precision loss.
- Which characters are valid in decimal?
- Base-10 decimal uses the digits 0–9. Spaces, underscores and an optional 0x/0b/0o prefix are ignored; any other character is flagged as invalid.