Polybius Square Cipher — Free Online Tool

Convert letters to row-column number pairs with the 5×5 Polybius square (I/J shared). Polybius Square Cipher is a free online tool from the ToolsRift Text Encoding Tools collection. It runs entirely in your browser — nothing to install, no signup, and your data never leaves your device.

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How to use Polybius Square Cipher

  1. Open the Polybius Square Cipher above — it loads instantly, no account needed.
  2. Enter or upload your input. Everything is processed locally on your device.
  3. Get your result immediately and copy or download it with one click.

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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