Thermo Sudoku
Digits must strictly increase along thermometer shapes
Thermo Sudoku is fully playable. Choose a difficulty and start solving.
Digits grow steadily from each thermometer's bulb to its tip — never equal, always rising. Line length does the heavy lifting: long thermometers pin their cells into narrow windows before a single digit is placed. A favourite stepping stone into modern variant solving — simple rule, deep consequences.
For the complete rules, worked examples and solving techniques, read the full How to Play Thermo Sudoku guide.
Like all Sudoku variants, Thermo Sudoku builds on the classic 9×9 foundation. Every row, column, and 3×3 box must contain each digit from 1 to 9 exactly once. The variant constraint is added on top of these standard rules, never replacing them.
If you're new to Sudoku, start by learning the basic rules and techniques before attempting variants.
Techniques Useful for This Variant
| Technique | How it applies |
|---|---|
| Pencil Marks / Notes | Essential for tracking candidates alongside the variant constraint |
| Obvious Singles | Cells narrowed to one candidate by the combined constraints |
| Hidden Singles | Digits with only one valid cell in a unit after variant elimination |
| Pairs and Triples | Locked candidates exposed by the additional constraint |