Thermometer puzzle vs Thermo-Sudoku
Search for "thermometer puzzle" and you will find two different games. Both draw thermometers on a grid, but one is about shading cells and the other is about placing digits. Here is how to tell them apart.
Part of the complete guide to thermometer puzzles · guide 1 of 7
The short answer
A thermometer puzzle asks you to shade cells: fill thermometers with mercury from the bulb so that each row and column has the right number of filled cells. Thermo-Sudoku asks you to write digits: solve a normal Sudoku in which the digits along each thermometer must increase from the bulb.
Side by side
| Thermometer puzzle (Thermometers) | Thermo-Sudoku | |
|---|---|---|
| You place | Mercury (shaded cells) | Digits 1–9 |
| Clues | Counts beside each row and column | Given digits inside the grid |
| Thermometer rule | Fill from the bulb with no gaps | Digits increase from the bulb |
| Other rules | None | All standard Sudoku rules (rows, columns, 3×3 boxes) |
| Grid sizes | Any size (4×4 to 15×15 here) | Usually 9×9 |
| Core skill | Counting and bounds | Digit placement and ordering |
How a thermometer puzzle works
The grid is completely covered by thermometers. You decide how far each one is filled. The only rules are that mercury starts at the bulb and has no gaps, and that the number of filled cells in every row and column matches its clue. The full rules, with diagrams, are in how to play.
How Thermo-Sudoku works
Thermo-Sudoku is a standard Sudoku, with each row, column and 3×3 box containing 1–9 once, plus a few thermometers drawn over the grid. Along each thermometer, digits must strictly increase starting from the bulb. Some puzzle setters use a "slow thermometer" variant in which digits may also stay the same. A thermometer of length 9 therefore forces 1–9 in order, and a thermometer of length k means its bulb is at most 10 − k.
The idea they share
Both puzzles use the thermometer as an ordering constraint (in thermometer puzzles this is what limits each tube to L + 1 states; see the math): the bulb comes first, and every later cell depends on the ones before it. In Thermo-Sudoku that means each digit is bigger than the last. In Thermometers it means a cell can only be filled if everything before it is filled. Solvers who enjoy one often enjoy the other, because both reward noticing how a single cell limits the whole tube.
Which should you play?
- If you like Sudoku and number placement, try Thermo-Sudoku.
- If you like nonograms, Battleships or other shading puzzles, thermometer puzzles will feel natural. See how they compare.
- If you want something you can learn in two minutes and play at any size (see sizes and variants), start with a 6×6 thermometer puzzle.
Questions
Which one is ThermometerPuzzle.com about?
Is Thermo-Sudoku harder?
Do the strategies carry over?
Play the shading puzzle
This site is all about the thermometer puzzle (Thermometers).