# Polybius Square > Decode and encode the Polybius square cipher, which turns each letter into its row and column in a 5×5 grid (I and J share a cell). - Page: https://linguaholic.com/tools/polybius-square/ - Type: free online tool (Converters & translators), no sign-up, runs in the browser - Publisher: Linguaholic (https://linguaholic.com/), made by Marcel Iseli - Last updated: October 3, 2026 - Open it pre-filled: https://linguaholic.com/tools/polybius-square/?text=2315313134&mode=decode - `text`: text to encode, or number pairs to decode (spaced or run together; wider gaps or / between words) (for example `hello`) - `mode`: direction: encode (default) or decode (for example `decode`) - `open`: open a section: steps (the 5×5 grid and worked letters), frequency (letter counts) or identify (which cipher is this?) (for example `steps`) ## What is the Polybius square? The **Polybius square** lays the alphabet out in a grid of five rows and five columns and writes each letter as two digits: its row and then its column. A sits in row 1, column 1, so it is `11`; H is in row 2, column 3, so it is `23`. The whole word HELLO becomes `23 15 31 31 34`. The alphabet has 26 letters and the grid has 25 cells, so two letters have to share. In the standard English square, I and J share a cell. The idea goes back to the Greek historian Polybius, which is why it is also called the **Polybius cipher**, the Polybius checkerboard, or simply the 5×5 grid cipher. ## How to use the Polybius square decoder and encoder 1. Choose **Encode** to turn letters into number pairs, or **Decode** to turn pairs back into letters. 2. Type your message, or paste the numbers. Each letter is a pair of digits from 1 to 5, written with a space between pairs. 3. Tap **Copy** to save the result. The grid view in the tool shows the row and column of each letter, so you can follow the steps. If you are not sure your numbers are a Polybius square at all, check the digits: if every digit is between 1 and 5 and the total count is even, it probably is. The tool’s cipher helper can make that guess for you. ## Frequently asked questions **What is the Polybius square?** The Polybius square is a 5×5 grid of letters that turns each letter into two digits: its row and its column. A is 11, B is 12 and Z is 55. Because the grid has 25 cells, I and J share one. **How do you read a Polybius square?** Read the row first and the column second. In 23, the 2 means row 2 and the 3 means column 3, which is H in the standard grid. **How do you decode a Polybius square cipher?** Split the digits into pairs and look each pair up in the grid: first digit for the row, second for the column. In the tool, choose Decode and paste the pairs with spaces between them. **Why do I and J share a cell in the Polybius square?** The alphabet has 26 letters and the grid only 25 cells, so two letters have to share. I and J is the usual choice; some versions merge C and K instead, as the tap code does. **How do you make a Polybius square with a keyword?** Write the keyword into the grid first, skipping any repeated letters, then fill the remaining cells with the unused letters in alphabetical order. Both sides need the same keyword to read the message. **What is a 6×6 Polybius square?** A 6×6 square has 36 cells, enough for all 26 letters and the digits 0 to 9, so no letters have to share. Its pairs use the digits 1 to 6. **Who invented the Polybius square?** It is named after the Greek historian Polybius, who in the second century BC described a torch-signaling system built on a letter grid. He credited the method to Cleoxenus and Democleitus and said he improved it. **What is the difference between the Polybius square and tap code?** Tap code uses the same 5×5 grid but drops K (tapped as C) and keeps J, and it sends the row and column as groups of taps instead of digits. **Is the Polybius square cipher secure?** No. Each letter always becomes the same pair of digits, so it can be broken by counting which pairs appear most often. It is ideal for puzzles, escape rooms and worksheets. **Is this Polybius square tool free and private?** Yes. It runs entirely in your browser with no sign-up, and nothing you type is uploaded or stored. ## Data sources The code breaker's English letter frequencies and word checks come from Linguaholic’s English dictionary, built from the open ENABLE and SCOWL word lists. Licenses and notices: https://linguaholic.com/tools/data/dict/v1/NOTICE.txt ## Related tools - [Tap Code](https://linguaholic.com/tools/tap-code/): Translate text to tap code and back: the 5×5 knock code American prisoners of war tapped through cell walls, with the full chart and how to tap it. - [A1Z26 Cipher](https://linguaholic.com/tools/a1z26-cipher/): Decode and encode the A1Z26 cipher, where A=1, B=2 and Z=26: letters to numbers and numbers to letters, with a full chart and puzzle tips. - [Bacon Cipher](https://linguaholic.com/tools/bacon-cipher/): Encode and decode the Bacon (Baconian) cipher, which writes each letter as five A/B symbols, with both alphabets and how to hide and find secret messages. - [Rail Fence Cipher](https://linguaholic.com/tools/rail-fence-cipher/): Encode and decode the rail fence (zigzag) cipher with 2 to 10 rails, see the zigzag drawn out, or crack a message when you do not know the key. - [Caesar Cipher](https://linguaholic.com/tools/caesar-cipher/): Encode and decode the Caesar shift cipher with any shift from 1 to 25, or crack a message without the key: every shift is tried and ranked for you. - [Morse Code Translator](https://linguaholic.com/tools/morse-code-translator/): Translate text to Morse code and decode it back, hear it as adjustable-speed sound with a visual flasher, and read the full Morse alphabet, number, and punctuation chart.