A LITTLE FOCUS. A FRESH START.
Play Thermo Sudoku
Play free Thermo Sudoku online. Digits increase from each thermometer bulb, adding ordered clues to five levels of Sudoku puzzles.
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Website saves stay in this browser and don’t transfer to the app.
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The game loads here. Choose a difficulty to start or resume a puzzle.
LEARN THE TWIST
How to play Thermo Sudoku
Thermo lines have a direction: numbers strictly increase away from the bulb. Renban lines use a consecutive set in any order instead.
The rules
Fill each row, column, and 3×3 box with 1–9, without repeats. Digits strictly increase along each thermometer, starting at its round bulb. They do not need to be consecutive.
A useful first move
Use the thermometer’s length to bound each cell. Once a middle digit is known, every earlier cell must be smaller and every later cell must be larger.
A four-cell thermometer can read 1, 3, 6, 9 from bulb to tip; consecutive digits are not required. Its bulb cannot exceed 6, because three larger digits must fit after it.
Controls, difficulty, and saved games
Choose Beginner, Easy, Medium, Hard, or Expert above. Select an empty cell, then tap a number or use your keyboard. Notes let you pencil in candidates; three hints are available. Three mistakes end the puzzle.
Every mode and difficulty keeps a separate save in this browser. You can switch puzzles and return to your place. Clearing site data removes these saves; they do not sync with another device or the iPhone app. Settings include night mode and optional automatic cell advancement.
Correct entries earn points. High scores are stored by mode and difficulty and update only when beaten; completed-puzzle count and day streak are shared.
FIFTEEN WAYS TO PLAY
Explore all Sudoku modes
A familiar grid, a different kind of logic. Every mode is free to play in your browser.