# Seed phrases (BIP 39)

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.

Canonical page: https://mybitcoinexplorer.com/learn/seed-phrases-bip39
Topic: Keys and addresses
Published: 2026-10-29
Updated: 2026-10-30


## Words instead of numbers
A [private key](https://mybitcoinexplorer.com/learn/private-keys) 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.

> Diagram: A 12-word seed phrase (example only) — 

## How it works
1. The wallet generates random **entropy**: 128 bits for 12 words, 256 bits for 24.
1. It adds a small checksum (4 or 8 bits).
1. It splits the result into 11-bit chunks. Each chunk (0–2047) picks a word.
1. The words are turned into a 512-bit **seed** that an [HD wallet](https://mybitcoinexplorer.com/learn/hd-wallets-bip32) 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](https://mybitcoinexplorer.com/learn/seed-passphrase).
- See [How to back up a Bitcoin wallet](https://mybitcoinexplorer.com/learn/backing-up-a-wallet).

> The first four letters of each word are unique in the English list, so writing four letters is enough to recover the word.


## 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.

## Related lessons

- [HD wallets (BIP 32)](https://mybitcoinexplorer.com/learn/hd-wallets-bip32)
- [How to back up a Bitcoin wallet](https://mybitcoinexplorer.com/learn/backing-up-a-wallet)
- [The seed passphrase ("25th word")](https://mybitcoinexplorer.com/learn/seed-passphrase)
- [Randomness and entropy](https://mybitcoinexplorer.com/learn/randomness-and-entropy)