A seed phrase is 12 or 24 words that encode the randomness behind every key in your wallet. Learn how it works, and how to store it safely.
Words instead of numbers
A private key is a huge number that's easy to mistype. A seed phrase encodes the randomness behind all your keys as 12 or 24 words from a fixed list of 2,048.
How it works
- The wallet generates random entropy: 128 bits for 12 words, 256 bits for 24.
- It adds a small checksum (4 or 8 bits).
- It splits the result into 11-bit chunks. Each chunk (0–2047) picks a word.
- The words are turned into a 512-bit seed that an HD wallet uses to create every key.
The checksum means a random typo in a word is usually detected.
Keep it safe
- Write it down on paper or metal. Never photograph it, store it in the cloud, or type it into a website.
- Anyone with these words can take everything. No legitimate support team will ask for them.
- Consider adding a passphrase.
- See How to back up a Bitcoin wallet.
How the last word works
The final word isn't fully random: part of it is a checksum of the other words. That's why a made-up list of 12 valid words usually fails, and why wallets can warn you about a typo when restoring.
Seed phrase vs private key
| Seed phrase | Private key | |
|---|---|---|
| Controls | Every key in the wallet | One key |
| Format | 12 or 24 words | 64 hex characters or WIF |
| Use | Backup and restore | Signing, rarely handled directly |
Key takeaways
- A seed phrase encodes 128 or 256 bits of randomness as 12 or 24 words.
- Every key in an HD wallet comes from it.
- Whoever has the words controls the funds; keep them offline.
Common questions
Is 12 words safe enough?
Yes. 128 bits of entropy is far beyond brute force.
Can I use my seed in another wallet?
Usually, if both support BIP 39 and the same derivation paths. Check that your balance appears before relying on it.
What if someone sees my seed phrase?
Move your funds to a new wallet with a fresh seed immediately; anyone who saw it can spend them.
Can I store my seed in a password manager?
Many experts advise against storing seeds digitally. Paper or metal, kept offline, is the usual recommendation.