How to play Thermometers
Fill thermometers with mercury from the bulb up, with no gaps, so every row and column has the right number of filled squares. Also known as Thermometer puzzle, Thermo grid.
The rules
- The grid is divided into straight thermometers, each with a round bulb at one end.
- Mercury fills a thermometer from its bulb towards its tip with no gaps. A thermometer may be empty, partly filled or completely full.
- The number beside each row and below each column is how many of its squares are filled.
Playing Thermometers on Puzzle Solvers
- Choose a size and a difficulty, then press New Puzzle.
- With Fill to here, tap a square on a thermometer to fill it from the bulb up to that square. Tap the top of the mercury to lower it by one.
- Mark empty puts a dot in squares you know stay empty; drag to dot several. Right-click also dots.
- Counts turn green when a row or column is right; Hint explains the next deduction.
Using the Thermometers solver
- Choose the size, draw each thermometer from bulb to tip and type the counts (or press Sample).
- Press Solve and step through: empty lines, full lines and how each thermometer fills from its bulb.
A worked example
In a 6×6, row 2 shows 0: all six squares are empty, so every thermometer crossing row 2 stops before it.
Column 4 shows 6, so it is completely full — and the thermometer that starts in column 1 and runs across to column 4 must be filled all the way from its bulb.
Strategies
- Zeros first. A row or column with 0 is completely empty — and so is every square further from the bulb on any thermometer passing through it.
- Full lines. When a count equals the length of the line, every square is filled — and so is everything between those squares and their bulbs.
- Bulb logic. If any square of a thermometer is filled, every square between it and the bulb is filled too. If a square is empty, every square beyond it is empty.
- Lying along a line. A thermometer lying along a row with a small count can fill only a few squares; one crossing it can fill at most one.
- Count what is left. Subtract the squares you know are filled from the count, then see where the rest can still fit.
Common mistakes
- Filling the top of a thermometer while leaving a gap below it.
- Forgetting that the bulb end can be at either end — look for the round end.
- Counting a row before checking the thermometers that cross it.
Where it comes from
Thermometer puzzles became popular in puzzle apps and magazines in the 2000s and are a classic of logic-puzzle collections. They teach the same ‘fill in order’ reasoning as many maths problems.
Frequently asked questions
Can a thermometer be empty?
Yes — empty, partly filled or full are all allowed.
Are thermometers always straight?
Here they are: each one runs straight across or down.
Is there always one answer?
Yes — every puzzle here is checked to have exactly one solution.
How do I solve one from a book?
Open the Thermometers Solver, draw the thermometers, type the counts and press Solve.
Keep going
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