Guides5 min read
Polybius Cipher: How to Encode & Decode
Polybius cipher explained: the full 5x5 grid, how letters become row-column coordinate pairs, and worked encode/decode examples by hand.
Polybius square cipher
Turn text into Polybius square number pairs, or decode them back. Free, private — nothing leaves your device.
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Number pairs0 characters
Your Polybius result will appear here.Everything you need to read a Polybius square
Both directions
Switch between text to numbers and numbers to text without leaving the page.
Live results
The result updates as you type. No button to press.
Flexible number input
Paste pairs separated by spaces or run together, like 2315313134. Both decode the same.
100% private
Runs entirely in your browser. Nothing you type is uploaded or stored.
Encode or decode in three steps
- 1
Pick encode or decode
Choose Encode to turn text into number pairs, or Decode to turn number pairs back into text.
- 2
Type or paste your text
Each letter becomes its row and column in the 5x5 square, so A is 11 and Z is 55. For decoding, paste the pairs with or without spaces.
- 3
Copy or download the result
The result updates live. Copy it, download it as a .txt file, or use swap to run it back the other way.
Built for learning, puzzles, and quick checks
The Polybius square is an ancient way to turn letters into numbers. It's a staple of puzzles and tap codes, not a way to protect secrets.
Learning ancient cryptography
See the square Polybius described around 150 BC turn a message into numbers.
Puzzle hunts and escape rooms
Number pairs made of 1 to 5 are a classic Polybius clue. Paste them and read the message.
Checking homework
Verify a hand-worked square instead of counting rows and columns.
Tap codes and prison knocks
The same grid underlies the tap code, so you can see how knocks map to letters.
Frequently asked questions
What is the Polybius square cipher?
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It's a cipher that writes the alphabet into a 5x5 grid, with rows and columns numbered 1 to 5. Each letter is replaced by its row number then its column number, so A is 11, B is 12 and Z is 55. It's named after the Greek historian Polybius.
How do I decode a Polybius square?
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Switch to Decode and paste the number pairs. Each two-digit pair is a row then a column, which points to one letter in the grid. For example 23 is row 2, column 3, which is H.
Why are I and J the same?
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A 5x5 grid has 25 cells but the alphabet has 26 letters, so I and J share one. When decoding, you tell them apart from context, for example 24 could be either letter.
What does the / mean?
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It marks a space between words, since the grid has no cell for a space. Other punctuation and digits can't be carried and are left out.
What if my numbers include 0, 6, 7, 8 or 9?
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They aren't valid, because the square only uses the digits 1 to 5. The tool tells you which digit is the problem. Some puzzles use a different grid or a keyword-mixed square, which this tool doesn't cover.
Is the Polybius square cipher secure?
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No. It's a fixed substitution, so the same letter always gives the same numbers and frequency analysis breaks it. It's for puzzles and learning only.
Is my text uploaded anywhere?
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No. Everything runs in your browser, and nothing you type is sent to a server.
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