Polybius Square Cipher Encoder & Decoder
Encode and decode the Polybius square cipher, which turns each letter into a pair of numbers from a 5×5 grid (I and J share a cell).
What is the Polybius square?
The Polybius square arranges the alphabet in a 5×5 grid and encodes each letter as a pair of numbers: its row and its column. Because the grid holds only 25 cells, the letters I and J share one cell. It dates back to the ancient Greek historian Polybius.
How to use it
- Choose Encode or Decode.
- Type your text, or paste number pairs to decode.
- Tap Copy to save the result.
How the Polybius square works
Reading across the grid, A is at row 1 column 1 (11), B is 12, and so on. Each letter becomes a two-digit number from 1–5. Decoding looks each pair back up in the grid. Turning letters into number pairs makes the Polybius square a handy building block inside larger ciphers.
Polybius and tap code
The tap code uses the same 5×5 idea but drops the letter K (using C instead) and expresses the coordinates as taps rather than digits.
More codes and ciphers
Explore the rest of the family: the Caesar Cipher, Atbash, Vigenère, and A1Z26. For other encodings, try the Morse Code Translator and the Binary Translator.
Free and private
This Polybius square tool runs entirely in your browser — free, with no sign-up, and nothing you type is uploaded or stored.
Frequently asked questions
- What is the Polybius square?
- The Polybius square arranges the alphabet in a 5×5 grid and encodes each letter as its row and column numbers. Because the grid has 25 cells, I and J share one cell.
- How do I decode Polybius square numbers?
- Choose Decode and paste the number pairs (each two digits from 1–5, separated by spaces). The tool looks up each pair's row and column to recover the letter.
- Is Polybius the same as tap code?
- They use the same idea of a 5×5 grid. Tap code omits the letter K (using C instead) and expresses the coordinates as taps, while the classic Polybius square merges I and J and uses digits.
- Is it free and private?
- Yes — it runs entirely in your browser with no sign-up, and nothing you type is uploaded.
More free tools
- Morse Code TranslatorTranslate 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.
- Roman Numeral ConverterConvert numbers to Roman numerals and back, turn any date into Roman numerals for tattoos, and read the full chart from 1 to 1000.
- Binary TranslatorTranslate text to binary code and back, convert between decimal and binary numbers, and read the full binary alphabet chart.
- NATO Phonetic AlphabetSpell any word or name in the NATO phonetic alphabet (Alpha, Bravo, Charlie…), hear it read aloud, and browse the full chart with pronunciations, numbers, and the police alphabet.
- Braille TranslatorTranslate English text to Grade 1 Braille and Braille back to text, and read the full Braille alphabet and number chart.
- Hex to TextConvert hexadecimal to readable text and text to hex instantly, both directions, with a full hex ASCII reference chart. Private and works offline.