Free printable Thermometers with answers
A thermometers puzzle is a logic puzzle played on a grid tiled with thermometers, each a straight run of squares with a round bulb at one end. Mercury fills a thermometer from its bulb and never skips a square, and the numbers beside each row and column count the filled squares in that line. That is the whole of it: no arithmetic beyond counting, and no rule you have to be told twice.
By size
A bigger board is harder, and so is a longer thermometer, though not in the way you would guess: longer tubes are what make a big board solvable at all. The top grade takes about twice the deduction of the first, and is the only one where a board regularly needs you to try a level and see what breaks.
Easy thermometers puzzles
Free printable easy thermometers puzzles with answers. A small board, short tubes, and a solve that comes straight off the row and column counts. Print with the answer. No sign-up.
Medium thermometers puzzles
Free printable medium thermometers puzzles with answers. An eight by eight board of fourteen tubes, still solvable without ever guessing.
Hard thermometers puzzles
Free printable hard thermometers puzzles with answers. A ten by ten board with tubes up to twelve squares long.
Expert thermometers puzzles
Free printable expert thermometers puzzles with answers. A twelve by twelve board where the deduction chain runs twice as long.
Evil thermometers puzzles
Free printable evil thermometers puzzles with answers. The biggest board we print, with tubes sixteen squares long. Still exactly one answer.
By audience
It is the gentlest logic puzzle we print. The rule comes from an object everyone has seen, and at the easier grades nothing ever has to be guessed and taken back.
Thermometers puzzles for beginners
Free printable thermometers puzzles for beginners with answers. Learn the one rule on a small board, with the answer on page two.
Thermometers puzzles with no guessing
Free printable thermometers puzzles that solve by pure deduction. Every square follows from the counts; nothing has to be tried and taken back.
Large print thermometers puzzles
Free printable large print thermometers puzzles with answers. A small board printed big, with the bulbs easy to pick out. No sign-up.
One fill, every time
Filling a tiling of thermometers to random levels always gives a legal board, because mercury that rises from the bulb cannot leave a gap and the counts are read off the result rather than chosen. What it almost never gives is a board its own numbers pin down: there are only as many constraints as the board has rows and columns, against one unknown per thermometer. So every puzzle here is searched for, not constructed, and checked by the same solver our Publisher Studio uses before it prints. The answer prints at the back.
How to solve a thermometers puzzle
The grid is tiled with thermometers, each a straight run of squares with a round bulb at one end. Fill each one from its bulb, never skipping a square, so that the numbers beside each row and column count the filled squares in that line.
The method
- 1Start with the lines that have no choice. A row or column numbered 0 is entirely empty, and one numbered the full width of the board is entirely filled. Both decide every square in the line at once, and both usually decide parts of several thermometers that run across it.
- 2Work each thermometer from both ends. A square you know is empty makes every square further from the bulb empty too, and a square you know is filled makes every square back down to the bulb filled. One deduction anywhere on a thermometer travels the whole length of it.
- 3Count what a line still needs, not what it has. Subtract the squares you have already filled from the line number. What is left has to come from the thermometers still undecided in that line, and often only one way of splitting it fits.
- 4Use the most a thermometer could give. If a line needs four and the thermometers crossing it could supply at most four between them, every one of them is filled as far as that line. The same argument upside down empties them when a line has nothing left to give.
- The one rule people get wrong
- Mercury rises from the BULB, not from the top of the page. A thermometer drawn pointing left fills from its right-hand end, and the bulb is the only thing on the board that says which end that is, which is why it is drawn so much wider than the tube.
- What the answer page shows
- The same board with the mercury drawn in, so each thermometer shows at a glance how far up it was filled.
- How the grades differ
- A bigger board, tiled with longer thermometers. The longer ones sound easier and are what make a big board work at all: a thermometer has only as many states as it has squares, so a large grid of short ones leaves the numbers with far too little to pin down.
- Is it the same as a nonogram?
- No. Both count filled squares along the rows and columns, but a nonogram tells you the runs in a line and leaves you to place them, while here the runs are printed on the board and the only question is how far along each one the mercury reaches.
- Good for
- Anyone who likes a puzzle that is mostly careful arithmetic.
Make one now
Pick a board, then print the puzzle and its answer. No sign-up, no watermark.