Word Sudoku & the Supply of Puzzles
Sudoku played with the nine letters of a word — and a count of how many such puzzles can exist at all, which is smaller than the number of words that qualify.
Click a cell then press a letter, or pick one from the tray. Backspace clears a cell. One row spells the source word.
Only one nine-letter word in nine can be a puzzle
A Word Sudoku needs nine letters that are all different, because two identical symbols cannot both sit in the same row. That is a much narrower requirement than it sounds. Of the 274,937 words in the dictionary shipped with this site, 41,231 are nine letters long — and only 4,710 of those repeat no letter, which is 11.42%. A single doubled letter disqualifies all the rest.
And the real supply is smaller still, because the grid is built from a set of letters rather than from a word. Two words with the same letters give the same grid — they are one puzzle wearing two names. Collapsing anagrams takes 4,710 words down to 4,182 distinct letter sets: 528 of the words, 11.2%, duplicate a grid that already exists.
| Words sharing a letter set | How many sets |
|---|---|
| 1 | 3,757 |
| 2 | 348 |
| 3 | 57 |
| 4 | 14 |
| 5 | 6 |
A long thin tail: most letter sets are the only word with their letters, and just six sets
manage five words apiece. One of those is aceinorst —
actioners, anoretics, creations, narcotise, reactions.
The most likely nine letters are themselves a word
Letter usage across the qualifying words is heavily skewed:
| Commonest | Appears in | Rarest | Appears in |
|---|---|---|---|
| E | 75.5% | Q | 1.80% |
| I | 73.9% | J | 2.23% |
| A | 69.2% | X | 2.74% |
| S | 65.8% | Z | 4.12% |
| R | 62.7% | V | 9.45% |
Every letter of the alphabet appears somewhere, but the tail is thin: only 485 sets (11.6%) contain any of Q, J, X or Z, and just 14 contain two or more.
Take the nine commonest letters and you get A E I L N O R S T — and that exact set turns out to be a real one, five times over: orientals, relations, serotinal, tailerons, tensorial. The most probable set of letters in the supply is not a near-miss or an unpronounceable jumble; it is one of the largest anagram groups there is.
Four words in the whole dictionary have one vowel
| Vowels | Qualifying words |
|---|---|
| 1 | 4 |
| 2 | 629 |
| 3 | 2,576 |
| 4 | 1,419 |
| 5 | 82 |
The extremes are tiny. Exactly 4 qualifying words hold a single vowel — cymblings, schmaltzy, sprightly, triglyphs — and they would make brutal puzzles, since the row that spells the word gives you almost nothing to hold onto. At the other end only 82 words carry five.
This tool draws from 3,548 of the 4,710 qualifying words, filtered by a rule worth stating exactly rather than describing as taste: three or four vowels, and none of Q, J, X or Z. That is a legibility filter, not a frequency one. This dictionary is stored alphabetically and carries no frequency data at all, so any claim about which words are "common" would be invented rather than measured — and the honest move is to say what the rule is and let you judge it.
How to use
- Press New puzzle to get a grid built from a nine-letter word.
- Click a cell, then press a letter key or pick one from the tray.
- Fill every row, column and three-by-three box with all nine letters.
- One row spells the source word — find it and the rest gets easier.
- Check your grid or reveal the answer at any point.
Frequently asked questions
What is Word Sudoku?
Ordinary sudoku with letters instead of digits. Every row, column and three-by-three box must contain all nine symbols exactly once, and here those symbols are the nine letters of a real word. One row of the finished grid spells that word out, which gives you a foothold the digit version does not have.
Which words can be used?
Only nine-letter words with no repeated letter, sometimes called isograms. The dictionary shipped with this site holds 41,231 nine-letter words and just 4,710 of them qualify, which is 11.42%. A single doubled letter disqualifies the rest, because two identical symbols cannot both sit in the same row.
How many Word Sudoku puzzles can exist?
Fewer than the number of qualifying words, because the grid comes from a set of letters rather than from a word. Anagrams produce the same grid, so 4,710 words collapse to 4,182 distinct letter sets. 528 of those words, 11.2%, duplicate a puzzle that already exists under a different name.
Which letters appear most often?
E turns up in 75.5% of the qualifying words, I in 73.9% and A in 69.2%. At the far end Q manages 1.80%, J 2.23% and X 2.74%. Every letter of the alphabet appears somewhere, but only 11.6% of letter sets contain any of Q, J, X or Z, and just fourteen sets contain two or more of them.
What is the most likely set of nine letters?
The nine commonest letters across all the qualifying words are A, E, I, L, N, O, R, S and T — and that exact set is itself a real one, five times over. It gives orientals, relations, serotinal, tailerons and tensorial, which is the largest kind of anagram group in the whole supply.
Are there words with hardly any vowels?
Four, in the entire dictionary: cymblings, schmaltzy, sprightly and triglyphs. Each has a single vowel. At the other extreme only 82 qualifying words carry five vowels, and the bulk of them, 2,576, carry three.
Why does this tool not use every qualifying word?
Many of the 4,710 are words almost nobody would recognise, and sending the whole list to your browser to pick one would be wasteful. The playable list is filtered by a rule we state exactly rather than by taste: three or four vowels, and none of Q, J, X or Z. That is a legibility filter and not a frequency one, because the dictionary is stored alphabetically and carries no frequency information at all.
Does every puzzle have exactly one answer?
Yes. Clues are removed one at a time and only kept out if the grid still has a single solution, which is checked by counting solutions rather than assumed. The check runs on the underlying digit grid, which is the same puzzle with the letters swapped back out.
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