Some wallets give you 12 words and others give you 24. It is natural to wonder if you got the weaker option. For nearly everyone, the answer is that it does not matter. This guide is part of our section on what a recovery phrase is.
What the words contain
A recovery phrase is a very large random number written in words. The BIP39 standard uses a fixed list of 2,048 words, so each word carries 11 bits of information. Part of the last word is a checksum, which lets your wallet catch most mistakes when you restore.
- 128 bits of randomness
- 4-bit checksum
- 132 bits in total
- Far beyond guessing
- 256 bits of randomness
- 8-bit checksum
- 264 bits in total
- Twice as much to back up correctly
The standard also allows 15, 18 and 21 words, but 12 and 24 are by far the most common.
| Words | Randomness | Checksum | Total bits |
|---|---|---|---|
| 12 | 128 bits | 4 bits | 132 |
| 15 | 160 bits | 5 bits | 165 |
| 18 | 192 bits | 6 bits | 198 |
| 21 | 224 bits | 7 bits | 231 |
| 24 | 256 bits | 8 bits | 264 |
Can 12 words be guessed?
No, as the maths of 2,048 words shows. A 12-word phrase has 2128 possibilities, which is about 340 undecillion, or 34 followed by 37 zeros. If every person on Earth checked a billion phrases a second, they would still need far longer than the age of the universe to get through them.
This assumes the words came from a proper random source, such as a hardware wallet or a well-known wallet app. A phrase you made up yourself is not safe at any length.
Is 24 words actually stronger?
On paper, much stronger. In practice, the extra margin is mostly theoretical. Bitcoin's keys are generally considered to give about 128 bits of security, so 12 words already roughly match the strength of what they protect. Twenty-four words go beyond it.
That does not make 24 words a bad choice. It gives extra margin, and many hardware wallets use it by default. It only means you should not lose sleep if your wallet gave you 12.
What length does not protect against
Every common way of losing crypto ignores phrase length entirely:
- A photo of your words synced to the cloud.
- Typing the words into a fake wallet site.
- A house fire that destroys your only copy, which a metal backup can survive.
- A family member finding an unprotected sheet of paper.
- Losing the paper and having no second copy.
Twenty-four words give no extra help with any of those. If anything, longer phrases mean more words to copy correctly.
Which should you choose?
Most of the time, you do not have to. Use what your wallet creates. If you are given a choice:
| If you… | Choose |
|---|---|
| Want a simpler backup and fewer chances of a copying mistake | 12 words |
| Want the extra margin and do not mind more writing | 24 words |
| Are unsure | Your wallet's default |
If you want more than a longer phrase
Extra protection against theft of your words comes from a different place. An optional passphrase, the 25th word, means a stolen phrase alone is not enough. It brings a new risk, though: if you forget it, nobody can help.