What is a Thermometers puzzle?
Thermometers is a visual logic puzzle played on a square grid filled with thermometer shapes. Each thermometer has a bulb, a path and a tip. Your job is to decide how much mercury belongs in every thermometer.
The numbers outside the grid tell you exactly how many cells are filled in each row and column. A thermometer can be empty, partly filled or completely filled, but the mercury always starts at the bulb and moves continuously toward the tip.
- Fill thermometer cells with mercury.
- Mercury must begin at the round bulb.
- Filled cells cannot skip over empty cells in the same thermometer.
- Every row clue and column clue must be matched exactly.
- The puzzles on this page are checked for a unique solution before they appear.
How to play Thermometers online
Click or tap a cell to cycle through filled, empty and unknown. Use filled cells for mercury and empty marks when a square cannot contain mercury. The grey thermometer outlines show the direction from bulb to tip.
Use Check when you want feedback without revealing the answer. Hint fixes one useful square, Undo steps back through your moves, and Solution shows the complete answer if you want to study the logic.
- Start by scanning rows or columns with a clue of zero.
- Mark a full row or column when its clue equals the grid size.
- When you fill a cell, every earlier cell in that thermometer must also be filled.
- When you mark a cell empty, every later cell toward the tip must also be empty.
- Keep comparing thermometer pressure with the remaining row and column totals.
Thermometers rules
The central rule is continuous fill. If the third cell of a thermometer is filled, the bulb, first cell and second cell must be filled too. If the second cell is empty, every cell farther toward the tip must also be empty.
The counting clues are exact. A row clue of 4 means exactly four filled cells in that row, not at least four. The same rule applies to every column clue.
- Thermometers may be empty, partly filled or full.
- Mercury never starts in the middle of a thermometer.
- Mercury never leaves a gap.
- Row clues count filled cells across the row.
- Column clues count filled cells down the column.
Thermometers strategy tips
Good Thermometers strategy comes from turning one clue into a chain of consequences. A zero row empties every cell in that row, and any empty mark can push farther toward the tip of its thermometer. A full row does the opposite: every cell in the row fills, and that fill can flow back to the bulb.
On harder puzzles, look for overlap. If a row needs three more filled cells and the only way to get them would also force extra cells in another row, that path is impossible. This kind of cross-checking is the heart of Thermometers logic.
- Use zero clues first because they remove whole lines immediately.
- Use maximum clues to force every cell in a line.
- Apply bulb-to-tip pressure after every fill or empty mark.
- Watch rows and columns that are almost complete.
- Compare the earliest possible filled cells with the latest possible empty cells.
Grid sizes and difficulty
The 6x6 Thermometers board is the friendliest place to learn because each clue has fewer cells to control. The 8x8 board feels like a compact daily puzzle, while 10x10 gives longer thermometer chains and more row-column interaction.
Easy puzzles use shorter chains and more direct clues. Medium puzzles add more curved thermometers and tighter counts. Hard puzzles use larger grids, longer pressure chains and clue patterns that require several deductions to work together.
- Choose 6x6 easy if you are learning the rules.
- Choose 8x8 for a balanced Thermometers puzzle online.
- Choose 10x10 for a bigger logic puzzle challenge.
- Easy, medium and hard change the thermometer layout and solving pressure.
- New puzzle creates another checked puzzle for the chosen setting.