Base32 Encoder/Decoder Free Online Tool 2026

Last updated March 22, 2026

What Is Base32 Encoding?

Base32 is a binary-to-text encoding scheme that represents arbitrary binary data using a 32-character alphabet. The standard RFC 4648 alphabet consists of the 26 uppercase letters A–Z plus the digits 2–7. Every 5 bits of input are mapped to one Base32 character, so 8 Base32 characters encode exactly 5 bytes. Padding characters (=) are appended to make the output length a multiple of 8.

The most common use case is encoding binary data in contexts where only alphanumeric characters are safe — for example, TOTP secret keys in two-factor authentication apps like Google Authenticator. When you scan a QR code to set up 2FA, the underlying secret is a Base32 string.

Base32 vs Base64: When to Use Which

Choose Base32 when the encoded string will be typed by humans (e.g., backup codes, secret keys) or used in case-insensitive contexts like DNS. Choose Base64 when storage efficiency matters more.

How the Encoding Works

The algorithm groups input bytes into 5-bit chunks and maps each chunk to a character in the alphabet. For the string Hello (5 bytes = 40 bits = 8 Base32 chars):

H        e        l        l        o
01001000 01100101 01101100 01101100 01101111

Split into 5-bit groups:
01001 00001 10010 10110 11000 11011 00011 01111

Map to alphabet (A=0, B=1, ... 2=26, 7=31):
J      B      S      W      Y      3      D      P

Result: JBSWY3DP (no padding needed — 40 bits / 5 = 8 chars exactly)

JavaScript Implementation

const ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567';

function base32Encode(str) {
  const bytes = new TextEncoder().encode(str);
  let bits = '';
  for (const b of bytes) bits += b.toString(2).padStart(8, '0');
  let out = '';
  for (let i = 0; i < bits.length; i += 5)
    out += ALPHABET[parseInt(bits.slice(i, i + 5).padEnd(5, '0'), 2)];
  while (out.length % 8) out += '=';
  return out;
}

function base32Decode(str) {
  str = str.replace(/=/g, '').toUpperCase();
  let bits = '';
  for (const c of str) {
    const idx = ALPHABET.indexOf(c);
    if (idx === -1) throw new Error('Invalid Base32 char: ' + c);
    bits += idx.toString(2).padStart(5, '0');
  }
  const bytes = [];
  for (let i = 0; i + 8 <= bits.length; i += 8)
    bytes.push(parseInt(bits.slice(i, i + 8), 2));
  return new TextDecoder().decode(new Uint8Array(bytes));
}

console.log(base32Encode('Hello'));  // → JBSWY3DP
console.log(base32Decode('JBSWY3DP')); // → Hello

Common Use Cases

• TOTP / 2FA secrets: RFC 6238 specifies Base32 for encoding HMAC keys in authenticator apps.
• DNS labels: Base32 is used in DNSSEC and some DNS-based protocols because DNS is case-insensitive.
• Onion addresses: Tor v3 .onion addresses are Base32-encoded public key hashes.
• File checksums: Some tools encode SHA hashes in Base32 for shorter, typeable strings.