Polybius square online

Polybius square online. Enter text, choose settings and encrypt or decrypt immediately. Learn how it works, its history, an example and its limitations.

How does the Polybius square work?

What is this method?

Writes letters as coordinates in a classic 5 × 5 grid.

How does it work step by step?

Place the alphabet in a 5 × 5 square, normally sharing one cell between I and J. Replace each letter with its row and column numbers; during decoding, each coordinate points back to a cell.

Example and practical use

In the standard 5 × 5 square, “REBUS” is represented by the coordinates 43 15 12 51 44.

How to use the tool

Choose encryption or decryption, enter a message and set the parameters required by the Polybius square. The result is calculated locally in your browser and can be copied or shared without sending the text to a server.

History of the cipher

The Greek historian Polybius described the system in the second century BCE. Its coordinates could transmit letters over a distance using groups of torches.

Security and limitations

This tool is educational. Classical ciphers can usually be broken with frequency analysis, repetition patterns or a small search through possible keys, so they should not protect confidential information.