How this calculator works
A telephone keypad groups the alphabet onto eight keys: 2 carries ABC, 3 carries DEF, 4 carries GHI, 5 carries JKL, 6 carries MNO, 7 carries PQRS, 8 carries TUV and 9 carries WXYZ. Encoding a word is unambiguous, because each letter has exactly one key. Decoding is not: the digits 4663 could be good or home, and only a dictionary, or the context of the sentence, tells them apart. This page uses a built-in list of common English words and shows every match it knows. It does not attempt to guess which one you meant.
Formula
Encode: each letter becomes its keypad digit, and each space becomes 0. Decode: the digit string is looked up in a table of words keyed by their own digit sequence; every word whose sequence equals the input is listed. A digit group with no entry returns no matches rather than a guess.
Worked example
hello encodes as 43556, because h, e, l, l and o sit on 4, 3, 5, 5 and 6. Decoding 43556 returns hello. Decoding 4663 returns good and home, which share the same keys, and decoding 843 returns the and tie. That ambiguity is the reason a T9 decoder needs a word list and why the same digits can mean different things in different sentences.
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Frequently asked questions
Why does one digit string give several words?
Each key carries three or four letters, so many letter combinations share a sequence. T9 phones used a dictionary and word frequency to rank the likeliest word as you typed. This page has no sentence context, so it lists every match from its small dictionary instead of pretending to know which one you want.
What do the digits 0 and 1 do?
In T9, 0 is the space between words and 1 is used for punctuation. This page writes a space as 0 when encoding. The decoder works on a single word at a time, because spaces would split the string into separate lookups; enter each word group on its own.
Is T9 still used?
It is rare on modern touch keyboards, which use a full keyboard or a predictive system with a much larger dictionary. T9 remains common on basic phones, in some car and TV remotes, and as a puzzle in retro software. The keypad layout itself is standardised in ITU-T E.161.
Why is my word missing from the results?
The dictionary is deliberately small and holds common English words only. Names, slang, technical terms and words of other languages are absent. A real T9 system used a much larger dictionary and learned from what you typed; this page trades coverage for a result you can check.
Does the case of my text matter?
No. The keypad mapping is the same for upper and lower case, and the decoder returns lower-case words. Punctuation is copied through when encoding, but the decoder accepts digits only, so remove punctuation before decoding.