Cipher
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Polybius Square Translator
The Polybius square turns every letter into two digits: its row and its column on a 5x5 grid. Type a message to see its coordinates, or paste digit pairs to read the letters back.
43 15 13 42 15 44 / 32 15 15 44 24 33 22
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Recent
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Polybius Square at a glance
- Type
- Keyless cipher
- Key space
- None (fixed 5x5 grid)
- Directions
- Encode and decode: Text to Coordinates and back
- Example
HELLO→23 15 31 31 34- Privacy
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It is one of the oldest number ciphers, and its grid idea underpins later systems like tap code. Everything happens in your browser; nothing is uploaded.
How the Polybius Square works
The 25 letters (I and J share a cell, since 26 letters cannot fit a 5x5 grid) are arranged in a fixed grid, five rows of five. Each letter is replaced by its row number followed by its column number, both counted from 1.
To decode, read each pair of digits as a row and a column, then find the letter sitting at that position in the grid. The chart below shows every letter's coordinates at a glance.
Examples
Polybius Square chart
Every letter at a glance. Use it to read or write by hand.
Why the Polybius square matters more than it looks
On its own the Polybius square is barely a cipher: a fixed grid, no key, and anyone who knows the layout can read it straight off. Its importance is as a building block, because turning each letter into a pair of digits is a step that other ciphers then build on.
Once every letter is two digits, those digits can be separated and recombined. That is exactly what the Bifid and Nihilist ciphers do, and it is what makes them meaningfully harder to break than the square alone: a single letter's information ends up spread across two positions in the output.
The square is also the delivery mechanism for tap code, where the coordinates become taps rather than digits. Same grid, different channel.
The variant to watch for is the grid itself. Twenty-six letters do not fit in twenty-five cells, so something must give. This tool merges I and J, which is the most common choice. Others drop K and send it as C. A message encoded with one convention will decode with a single wrong letter under the other, which is usually obvious in context but worth knowing when a decode reads almost right.
History and origins
The Greek historian Polybius described the square around 150 BCE, originally as a way to signal letters over long distances using torches, one group for the row and one for the column. It is one of the earliest recorded methods for turning letters into numbers.
The same grid idea resurfaced two thousand years later in very different forms, from military tap codes to number-based signalling, because a 5x5 grid of coordinates is easy to memorise and easy to send through almost any two-state medium: taps, flashes or flags.
Frequently asked questions
What happens to the letter J in the Polybius square?
A 5x5 grid has 25 cells for 26 letters, so I and J share one cell. J is treated as I both when reading the chart and when the translator decodes coordinates.
Is the Polybius square the same as tap code?
They share the same 5x5 grid idea, but tap code (used by prisoners of war) merges C and K instead of I and J, and signals the coordinates as taps rather than written digits. Try the tap code translator to see the difference.
Is the Polybius square secure?
No, it is a simple substitution with no key, so anyone who knows the standard grid order can decode it instantly. It is best known today as a teaching tool and a building block for other ciphers and codes.
Learn more
Go deeper on the ideas behind this tool.
Not sure this is the right tool?
If you have a message and you are not certain what it is, the cipher identifier reads the character set and the letter statistics and tells you which scheme it most likely uses, and why. It covers every code and cipher on this site.