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How to use Polybius Square Cipher

Type your text, and the tool converts each letter into its row-column coordinate pair on a 5×5 Polybius square (I and J share a cell).

Frequently asked questions

What is the Polybius square?

A 5×5 grid that maps each letter to a two-digit coordinate (row, column). Because 26 letters don't fit in 25 cells, I and J share one cell — a convention dating to Ancient Greece.

How is 'HELLO' encoded?

H is row 2 column 3 → 23, E → 15, L → 31, L → 31, O → 34, giving '23 15 31 31 34'.

What happens to J when decoding?

Every 24 (the I/J cell) decodes as 'I'. If your original text contained a J, it will read back as I — this is inherent to the classic square.

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