Puzzle Genius


Thermometers is a pure logic puzzle played on a square or rectangular grid filled with thermometer shapes. Each thermometer has a base (the bulbous end) and a top. In simple puzzles, thermometers may be placed horizontally and / or vertically. In more difficult levels, the thermometers may be ‘broken’ such that they span more than one column or row.

The objective of the game is to fill the thermometers sufficiently that the number of cells filled in a row and column of the grid corresponds to the numbers on the outside of the grid.

Here’s a small example Thermometers puzzle:

A small example of a thermometers puzzle.


  • Thermometers can be entirely unfilled, partially filled, or completely filled.
  • Thermometer always fill from the base toward the top. This is irrespective of the thermometer's actual orientation on the grid.
  • Each filled segment of a thermometer counts as one filled cell.

Here is what the example puzzle looks like when it has been solved:

The solution to the thermometers example puzzle.

Tips for Solving Thermometers

Start with Extremes. Look for rows or columns with a 0 written outside. This means no cell in that row or column is filled, so all thermometers crossing it remain unfilled beyond that cell. Similarly, if a row or column's clue equals its length (e.g., a clue of '5' for a row of 5 cells), then every cell in that row or column is filled.

Look for Forced Fills. If a thermometer segment in a row or column is filled, then all segments below it (toward the base) must also be filled. Conversely, if a segment is unfilled, all segments above it (toward the top) must be unfilled too.

 Use Partial Information. Even if you can't completely determine the fill status of a row, column, or thermometer, partial fills can help. For instance, if you have a row of 8 cells with a clue of '6', and two thermometers with bases in that row, you know at least some segments of those thermometers must be filled to meet the clue.

Mind the Gaps. If filling a thermometer segment would exceed the clue number for a row or column, then that segment (and those above it) must remain unfilled.

Use Pencil Marks. For cells you’re not sure about, mark potential fills lightly. If they lead to contradictions, you can erase and reassess.

Where to Play

Fancy filling some thermometers? We publish this puzzle occasionally in our free Puzzle Weekly magazine. You should totally sign up for that if you haven’t already, as it puts 28 brand new puzzles in your inbox every week.

You can also find lots of Thermometers puzzles in our Jumbo Adult Puzzle Book – which happens to include more than 500 puzzles of 20 different varieties.

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