What changes on Medium?
Medium Thermo Sudoku drops some of the starter numbers you saw on Easy and adds one more thermometer. That means more of the puzzle is solved from the bulb-to-tip rule, not from the obvious row/column clues. Don’t panic — every Medium puzzle on this site still has exactly one solution and you can always find it without guessing.
If Medium feels like a big jump from Easy, that’s normal. Most kids spend a couple of weeks at Easy before Medium starts to feel comfortable. For a refresher on the basics, the Thermo Sudoku page has the full rules with worked examples.
Three thermometer tricks to try
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Bulb-and-tip clamp
On any thermometer, write the smallest possible bulb and the biggest possible tip in your notes. The middle cells are clamped between those two — you can rule out lots of digits straight away.
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Walk the line
Once you place a digit on one thermo cell, immediately update the candidates on the cells before AND after it. Cells before must be smaller; cells after must be bigger.
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Length tells you a lot
A 4-cell thermometer needs four different digits, all going up. So the bulb must be 6 or smaller (so three more digits can fit), and the tip must be 4 or bigger.
How to spot a forced digit
A "forced digit" is when only one number can go in a cell, no matter how you look at it. Spotting them is the main skill on Medium. Here’s the order we recommend: check the row, check the column, check the 3×3 box, then check the thermometer (if the cell is on one). If that leaves only one legal number, write it in.
Sometimes the row and column leave 3 or 4 options, but the thermometer rule knocks out all but one. This is the pay-off for learning Thermo Sudoku — the line really does the work.
On cells that aren’t on a thermometer, solving feels exactly like classic sudoku. On thermo cells, always remember to include that fourth check.
When you get stuck
- ✏️ Turn on Auto Notes — on Thermo Sudoku this is doubly useful
- 🔎 Tap Check to make sure every filled cell is still correct
- 💡 Tap Hint to fill one cell (it counts in your stats, but it’s okay!)
- ↻ Tap Undo to go back if a guess turned out wrong
Ready for the next step?
When Medium Thermo Sudoku puzzles take you under 10 minutes, give Hard Thermo Sudoku a try. Hard puzzles have way fewer givens and you’ll need every trick from this page plus a few more.
Frequently asked questions
How long should Medium Thermo Sudoku take?
Most kids finish a Medium puzzle in 10 to 18 minutes. If it takes longer, that’s fine — use Notes and tap Check whenever you want to make sure you’re on track.
Can I switch back to Easy?
Of course — just tap the Easy tab at the top of the board. Your Medium puzzle saves automatically.
Are there more thermometers on Medium?
Yes, just one or two more. They’re still short, straight lines — easy to read but they cover more of the grid, so the puzzle has a tighter web of clues.
Does Auto Notes work with thermometers?
Yes. Our Auto Notes only marks digits that are legal under all the rules at once — including the thermometer rule. So your pencil marks are always correct.
Try other sudoku games
Different rules, same friendly board. Pick a sibling puzzle to play next.