What makes Expert so tough?
Expert Thermo Sudoku gives you the smallest number of starter clues we use anywhere on the site, and more thermometers than any other level. The thermometers are essentially the whole solving engine for the first half of the puzzle. You’ll need to hold a lot of information in your head (or in Notes) at once.
But every Expert puzzle on this site has exactly one answer, and you can solve it without guessing. Use logic, take breaks, trust your notes!
If Expert feels overwhelming, that’s normal — even adults find it tough. Spend a few weeks at Hard Thermo Sudoku first; the techniques are exactly the same, just with one or two more starter numbers.
Techniques worth memorising
- 🌡️ Bulb-and-tip clamp on every thermometer — apply it before you do anything else
- 🔢 Naked pairs and naked triples in rows, columns and boxes
- 🔄 "Walk the line" both directions: smaller before, bigger after
- 🔢 Hidden singles where a digit can only fit in one cell of a thermometer’s row, column or box
- 🎯 Length-based limits: a 3-cell thermo bulb is at most 7, a 4-cell thermo bulb is at most 6
Expert solving routine
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Auto Notes first
Tap it the moment the puzzle loads. You’ll see every candidate digit at a glance, with the thermometer rule already applied.
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Clamp every thermo
Walk each thermometer end-to-end and erase any candidate that’s out of range. This is the highest-value habit on Expert.
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Place from the ends
Bulbs and tips often have just one possible value. Solve those first — the middle of the thermo will fall right after.
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Hunt naked pairs and triples
After Auto Notes, look for two cells with the exact same two candidates on any row, column or box — those numbers are locked there.
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Place, repeat, win
Each placement narrows things down everywhere. Keep going until the board is full!
When you’ve mastered Expert
Once Expert Thermo Sudoku feels comfortable, try our toughest Expert 9×9 sudoku. It’s a different kind of challenge — no thermometers, pure row/column/box logic — but the same long-thinking patience pays off.
Or try Hyper Sudoku for puzzles that add four extra mini-boxes inside the grid, X-Sudoku for puzzles with two main diagonals, Killer Sudoku for puzzles that add cage sums, or Jigsaw Sudoku for puzzles with wiggly regions instead of 3×3 boxes. Very different puzzles, all built on the same "one of each in every region" idea.
Frequently asked questions
How long does an Expert Thermo Sudoku take?
Most kids who can solve Expert finish in 20 to 40 minutes. Some take more than an hour — that’s normal! There’s no time limit.
Can I really solve Expert without guessing?
Yes! Every puzzle on this site has exactly one solution and was checked by computer to be solvable with logic alone. If your guess turns out wrong, just tap Undo.
What if I’m really stuck?
Tap the Hint button — it fills one correct cell so you can keep going. Hints count in your stats, but they’re there to help.
Is there anything harder than Expert Thermo Sudoku?
On this site, Expert is the toughest thermo puzzle. Some grown-up sites have an "Extreme" or "Diabolical" level, but those are designed for adult sudoku-club regulars, not kids.
Try other sudoku games
Different rules, same friendly board. Pick a sibling puzzle to play next.