Every base represents the same underlying number. What changes is density and which characters are used — which matters when a value has to survive a URL, a filename, a case-insensitive system or a human reading it aloud.
The bases, and where each is used
| Base | Alphabet | Typically used for |
|---|---|---|
| 2 | 01 | Bit flags, permission masks, protocol fields |
| 8 | 0-7 | Unix file permissions |
| 10 | 0-9 | Human-facing numbers |
| 16 | 0-9a-f | Hashes, keys, memory addresses, colours |
| 32 | RFC 4648 | TOTP secrets, case-insensitive identifiers |
| 36 | 0-9a-z | Compact case-insensitive IDs |
| 58 | Bitcoin alphabet | Values a human transcribes |
| 62 | 0-9A-Za-z | Short URLs, compact IDs |
| 64 | Base64 | Binary in text channels |
Density in practice
A 128-bit value:
- Binary: 128 characters
- Hex: 32 characters
- Base32: 26 characters
- Base58: 22 characters
- Base62: 22 characters
- Base64: 22 characters
Base58 and Base62 land in the same place as Base64 while being URL-safe and, for Base58, transcription-safe. That is why short-link services and Bitcoin addresses use them.
Bit length is the useful readout
The bit length tells you how much entropy a value can hold. A token displayed as 22 Base62 characters carries at most 130 bits — and exactly that only if it was generated as random bytes. If it was generated as a counter, its bit length says nothing about its unpredictability.
This is the distinction between representation and entropy: converting a value to a denser base does not make it stronger. The entropy calculator measures the latter.
Leading zeros
Numeric bases drop leading zeros, because 007 and 7 are the same number. That matters for byte sequences: hex 00ff and ff are the same integer but different byte arrays.
Base58 handles this explicitly, encoding each leading zero byte as a 1 — which is why Bitcoin addresses beginning 1 do so consistently. If you are converting a fixed-width byte sequence rather than a number, use the hex converter, which preserves byte boundaries.
Frequently asked questions
Why is my Base64 output different from another tool's?
Probably leading zeros. This tool treats the input as a number, so leading zero bytes vanish. Byte-oriented conversion preserves them — use the Base64 encoder with hex input for that.
What is the largest value I can convert?
Arbitrary precision, using JavaScript BigInt. A 4096-bit RSA modulus converts without loss.
Which base for a short URL?
Base62. It is URL-safe without encoding, dense, and every character is a normal alphanumeric. Base58 if the code might be read aloud or typed from a printed page.
Is Base32 the same as base 32?
Not quite. RFC 4648 Base32 uses A-Z2-7, deliberately excluding 0, 1 and 8 because they are confusable. Numeric base 32 would use 0-9a-v. This tool shows the RFC 4648 form, since that is what TOTP and file formats use.