Rules
Thermometers is a filling puzzle. The board is a square of straight tubes. Each tube has a round bulb at one end and runs across or down. You fill mercury from the bulb toward the tip as one bar. It does not skip a cell. A number beside each row, and a number above each column, is how many cells in that line are filled. Zero is a real clue and means the line is empty.
A cross marks a cell you know is empty. Crosses are optional. An empty cell counts as not mercury. The corner is empty. No cell starts filled or crossed. The tubes and the numbers are given. You do not move them. Play is 6×6, 7×7, 8×8, and 10×10, and every one of those is easy. The daily puzzle is a 6×6. The grid is finished when the filled cells are the one solution and the outside numbers match.
Kakurasu is the familiar part: the numbers sit outside the grid, and you use two marks. Kakurasu shades a cell or crosses it so a weighted sum matches. Thermometers fills a tube from the bulb so a plain count matches.
Nonograms already teaches fill counts and crosses. Nonograms fills runs. Thermometers fills one bar from a bulb, and a cross can run on past the counted line to the tip.
- One bar from the bulb. Each tube has a round bulb at one end and runs across or down. Mercury fills from the bulb toward the tip as one bar. It does not skip a cell.
- Outside counts. A number beside each row, and a number above each column, is how many cells in that line are filled. Zero is a real clue and means the line is empty.
- A cross is optional. A cross marks a cell you know is empty. An empty cell counts as not mercury, so the grid can be finished with fills alone.
- Finished. The tubes and the numbers stay put. The grid is done when the filled cells are the one solution and the outside numbers match.
The 0 left of row 4 is six crosses. The 6 left of row 1 is filled back to the bulb. On row 2 the bar starts at the right-hand bulb and stops before the crossed tip. Bars, tubes, crosses, counts, and the frame are teal. The two bulbs on the 0 rows stay hollow. Crosses are optional: the same grid is finished if those fourteen empty cells are left unmarked and only the fills are present.
- Mercury
- Cross
- Bulb
- Outside number
- Count clashes
Choose Fill or Cross. Tap a cell, or drag along a tube. Fill sets the mercury from the bulb up to the cell you touch. Tap the cell at the current surface again to lower the level by one. A drag that visits several cells sets the level to the furthest cell and does not lower it. Cross marks the cell you touch and every cell from there to the tip. Tap a cross again to clear that stretch. A cross drag marks from the cell closest to the bulb through the tip. One stroke is one undo step. With a mouse, right-click places a cross, including when Fill is selected. A second right-click on a cross clears that stretch. There is no tap that cycles a cell through empty, fill, and cross.
Arrow keys move and stop at the edge. Space or Enter applies the selected mark. F or 1 fills. X, C, or 2 places a cross. M switches Fill and Cross. Backspace, Delete, or 0 clears the mark at the cell and the same mark toward the tip, so a fill does not leave a gap. Selecting a cell rings that cell and the clue chips of its row and its column. It does not tint the other cells in the row. The selected cell keeps its open face, or its done face when the line is already done.
A count turns teal only when the filled cells equal it and every cell on that line is marked. A count that already matches, while a cell is still open, stays the ordinary chip. On Kakurasu a matched sum turns teal while cells are still open. Here it does not. On the full-line grid later in this guide, after the two full rows are filled and the two 0 rows are crossed, column 1 already shows 2 against a clue of 2, and two cells in that column are still open, so that clue stays ordinary. A count turns red when the line is already past it, or when the cells still open cannot reach it. Only the clue chip turns red. The cells on that line are not washed. A gap turns the cell and the tube red.
Press Hint for one step the rules already force, with a sentence saying why. Hint lights the cells it writes and the one count it uses. It does not wash the rest of that line. Press Check when you want the board checked. Undo and Redo step through the moves. Reset clears the marks. The tubes and the numbers stay. When the mercury matches, the board turns teal: bars, tubes, crosses, counts, and frame.
The line under the tools reads "Tap to fill from the bulb up to a cell. Tap again to clear. M switches mode." Solved, that line and the dialog body read "Each thermometer is filled from the bulb, and the outside numbers match." The dialog title is "Solved!"
- Fill
- Cross
- Undo
- Redo
- Reset
- Hint
- Check
One line
Read one count at a time. A 0 empties a tube from where it meets the line out to the tip. A count that equals the length fills that tube back to the bulb. The other two sentences are still that one line: cross what is past the count, or fill the open cells when they are exactly what is left.
The how-to describes the whole line. One press writes one tube, except when the open cells are exactly what is left. That press fills every open cell on that one line, and it can be more than one tube. Two tubes on one 0 line take two presses.
A count of 0 Easy
A count of 0 means no mercury on that line. Each tube that meets the line stays empty from the meeting cell out to the tip. The how-to is right about the line. The button writes one tube per press. On this figure row 3 is 0 and two tubes share it. The press crosses the left tube, from its bulb through the tip, and leaves the other tube open. The next press crosses that second tube. It is not drawn. Row 1 on this same board is also 0, and it is one tube, so the first press crosses the whole row. That is why the figure already shows row 1 crossed. A 0 does not have to wait for the other counts.
Row 1 is already six teal crosses, and its 0 is the done chip. The press crosses row 3 from the bulb in column 3 through column 1. Those three cells are ringed. Each is a new cross on the wash. The 0 left of row 3 is lit. The tube from column 4 to column 6 stays open, and it is not washed. Row 1 is not washed. Hint says "This line is 0, so the thermometers that meet it stay empty from here to the tip."
A full line Easy
A count that equals the length of the line sees every cell, so the tube is filled back to the bulb. On a 6×6 that count is 6. Hint fills the tube in one press. It does not stop after the first cell. A second tube on the same full line is the next press. One 7×7 does that: one press fills four cells, and the next fills the other three. This figure's full line is one tube, and it is the third press, after both 0 rows are crossed.
Rows 4 and 5 are teal crosses, and both 0s are done chips. Row 1 has six cells and the clue is 6. Crossing any one of them would leave at most 5. The six cells are ringed, mercury included, from the left-hand bulb through the tip. The 6 is lit, even though the new marks complete the row. Rows 4 and 5 are not given the amber wash. Hint says "This line is full, so these cells are filled back to the bulb."
The next press on this board fills row 3, the other full line. It is not drawn. After both full rows, column 1's count is already met and the clue is still the ordinary chip, because two cells in that column are unmarked. The press after that crosses only the tip of row 2. That one cell is the same sentence as the next section.
Already enough Easy
If the filled cells on a line already equal the count, every tube that still meets the line is empty from that meeting out to the tip. The cells on the bulb side of the cut can stay open. The cells toward the tip are crossed even when they sit off the line. On this figure column 4 already has its two fills. The tube whose bulb is at the right of row 6 meets that column one cell in. The press crosses from the meeting cell through the left-hand tip. The two cells closer to the bulb stay open. The how-to's "cross the rest" runs to the tip, not only along the counted line.
Column 4's clue is 2, and two cells in that column are already filled. Any further mercury there would pass 2. The four cells from that column through the tip are ringed. Each is a new cross on the wash. The 2 above column 4 is lit. The bulb and the cell beside it stay open. The earlier rows are not given the amber wash. The two fills that met the count stay ink. Hint says "This line already has its count, so the remaining cells are empty."
The previous press, not drawn, crossed three cells of row 4 for this same column. Two of those cells sit off the column. On the finished-picture grid the same sentence is a single cross, because the meeting cell is the tip of row 2. That one cell is not a second picture.
Exactly what is left Easy
Count the cells on the line that are still open. If they are exactly the mercury still needed, fill them. The fill runs back to the bulb, so the new cells are one bar, not a gap. On this figure row 2's clue is 5, the tip is already crossed, and the other five cells are open. The press fills those five, from the right-hand bulb toward the tip. This board never says "too far". The five fills do not depend on that sentence.
A later column can fill every open cell on the line in one press, including more than one tube and cells off the line. One grid does that with seven fills, five of them off the column. It is not drawn. The one-cell version is the bulb left open in the next section. It is named there, not drawn here.
Rows 1 and 3 are ink mercury on the done wash. Rows 4 and 5 are teal crosses. The tip of row 2, and the tip of row 6, are teal crosses because column 1 is fully marked and matches 2. That clue is the done chip, not the hint. The five open cells of row 2 are ringed and filled from the bulb. The 5 is lit. The crossed tip is not washed amber, and row 6 is not washed amber. Leaving any one of the five empty would leave at most 4. Hint says "The open cells on this line are exactly the mercury still needed, so they are filled."
The cross on the tip is required. Before that cross, the next press is the one cell at the tip, not this fill. Not every grid says a count of 0, and not every grid says a full line. One 7×7 never says a count of 0. One 6×6 never says a full line. Every grid here says already enough, and every grid here says exactly what is left, at least once. The next section is still easy. It is the same ladder.
How far
The count also limits how far one tube may run, and how far it must run. The grids here use the first of those. They finish before the second.
Too far Easy
A tube that runs past the count would put mercury where the line has no room. Cross from the first cell past that room through the tip. The cells closer to the bulb can stay open. On this figure row 2's clue is 1 and the tube is six cells with the bulb on the left. The press crosses from the second cell through the tip and leaves the bulb open. The next press, not drawn, fills that bulb. That is "exactly what is left" as one cell.
On a real grid this sentence often comes before the fill on the same tube, because the line is not tight until the cut. The ladder still looks for a tight line first. One grid does the pair in that order on a row whose count is 3: three crosses toward the tip, then three fills back to the right-hand bulb. It is the same rule as this figure, and it is not a second picture.
Row 1 is already six teal crosses, and its 0 is the done chip. The bulb on row 2 can hold the one cell the row needs. Filling the next cell would make at least two, and the clue is 1. The five cells from there to the tip are ringed. Each is a new cross on the wash. The 1 is lit. The bulb is not washed, and row 1 is not washed. Hint says "Mercury past this cell would pass the line's count."
Not every easy grid says this. The grid in the rules picture never does. Some 6×6, 7×7, 8×8, and 10×10 grids never do either. The next sentence is in the same pass, after this one, and the grids here finish without it.
Must reach this far Easy
Look at the other tubes on the line and give each of them as much mercury as it is still allowed. If that is still short of the count, this tube has to reach a definite cell. Fill back to the bulb up to that cell. Hint would say "The line cannot reach its count unless the mercury gets this far." It names one tube.
This sentence is in the solver and in the how-to. It was not the next press on the grids here, including a partial that kept the first tubes of a solution and left the rest unknown. There is no picture. The grids finish with the five sentences above.
What if
The puzzles on this site finish with the sentences above. A grid that would need you to try one tube both ways is not one of these puzzles. Hint does not offer that try. If the deductions have stopped and the grid is not finished, Check or Undo is the next move, because a fill or a cross may be wrong.
When Hint has nothing to write, it says "No forced cell from here. The mercury or a cross may be wrong, so try Check or Undo." There is no picture for that try, and there is no second result where both ways force the same cells. The grids here finish before it.
Common mistakes
Check marks a count when the line is already past it, or when the open cells can no longer reach it. Only that clue turns red. The cells stay as they are. Mercury stays ink. A line that can still reach its count is not a mistake yet. A fill that simply is not the solution, and breaks nothing, stays quiet. A row can turn teal because the count matches and every cell is marked, while those cells are still the wrong tubes. Check does not compare the line with the answer until the whole grid is decided, and on these puzzles a full grid that matches every count is the solution.
Hint, on the play page, refuses while Check would fail. The toast is "This board has a mistake, so there is no hint yet." The pictures of broken boards show the coral clue and no amber ring. A direct look can still name the opening step, because a mark that disagrees with the solution is set aside before the search, and an over or a short is still a legal prefix. The button does not show that step. Applying it writes the opening line and leaves a wrong mark the step does not list.
The clue on row 2 is 5, and the row is filled to the tip, so the level is 6. The 5 turns coral. No cell is washed. The bar and the bulb stay ink. No amber ring. One extra fill on this row does not pass the column counts. Hint refuses until the extra fill is gone. A direct look still names the opening count of 0 on row 4, and applying it leaves all six fills where they are.
The bulb of row 5, the next cell, and the bulb of the short tube on row 6 are filled. Column 5 now holds two cells, and its clue is 1, so that count turns coral. No cell is washed. The extra fill beside the bulb is column 6, whose clue is 2, so that column is not the error. Row 5's clue is 4 and only two cells are filled. Row 6's clue is 3 and only one cell is filled. No amber ring. Hint refuses. A direct look names the opening count of 0 on row 1 and leaves the three fills.
Row 1's clue is 6. The tip is crossed, and the other five cells are open, so the most the row can add is 5. The 6 turns coral. No cell is washed. The cross stays the ordinary colour, because the cell itself is not the error. No amber ring. Hint refuses. A direct look names the opening count of 0 on row 4 and leaves the cross on the tip. That press does not repair the short row.
All six cells of column 5 are crossed, and the clue is 1. That count turns coral. No cell is washed. The six crosses stay the ordinary colour. No row clue turns coral: each row still has five open cells, and no row clue on this board is 6. No amber ring. Hint refuses. A direct look still names the count of 0 on row 1. The cross already on that row caps the tube, so the look writes the bulb and leaves the five crosses below it. The Cross tool on these horizontal tubes would also mark toward the tip, so a player does not reach these six cells with one tap. The picture is the checker's column.
The right-hand bulb on row 4 is filled, and nothing else is. That tube's solution is empty. Row 4's clue is 3, so one fill is not over. The level is 1, so there is a filled bulb and no bar. The mercury stays ink. No coral. The amber ring is the opening count of 0, on row 1, with crosses ready to write. The 0 is lit. If Hint runs, it crosses that row and leaves the bulb where it is. Check would not fail, so the button does show this hint.
Row 4 is crossed on the left tube and filled on the right tube. The solution does the opposite. The row tally is three fills and no open cells, and the clue is 3, so the 3 is the done chip, teal text, not coral. The three crosses are teal. The three fills are ink mercury on the done wash, and the bar runs to the tip. No amber on row 4. The amber ring is still the count of 0 on row 1. After that press, all six marks on row 4 are still there. Check does not complain, and it has not compared the row with the answer.
What to play next
Every size here is easy. There is no medium and no hard. A 6×6 can use a count of 0, a full line, a line that already has its count, the open cells that are exactly what is left, and a tube that would run too far. Not every grid says each of those. "Must reach this far" is a real sentence and was not needed on these grids. A try of one tube both ways is not offered. The boards above are teaching boards.
- Easy6×6The daily size. A count of 0, a full line, a line that already has its count, the open cells that are exactly what is left, and a tube that would run too far. Not every 6×6 says each of those.Play 6×6 →Today's daily →
- Easy7×7The same sentences. One 7×7 never says a count of 0 and opens on a full line. A full row of two tubes takes two presses.Play 7×7 →
6×6, 7×7, 8×8, and 10×10 come in easy only. The daily puzzle is a 6×6 easy grid: today's Thermometers and 6×6 easy. A new player can start on the daily, or on any 6×6.
Print a Thermometers pack. A single pack has eight puzzles. The starter pack has five, one of every size, including a print-only 12×12 that has the sheet to itself. Four 6×6 or 7×7 grids share a sheet. Two 8×8 or 10×10 grids share a sheet. Large print is one grid. The pages are black and white. Tubes, bulbs, and numbers print. Answer pages fill the mercury and keep the numbers. They do not print crosses. Amber, red, and teal do not print.
Kakurasu uses outside numbers and two marks, and the sum is weighted. Nonograms reads fill counts and crosses.
- GuideKakurasuOutside numbers and two marks. Kakurasu is a weighted sum.
- GuideNonogramsThe clues are fill counts and crosses.
- GuideSudokuEach digit once in every row, column and box.
- GuideHashiCount bridges, never cross, connect every island.
- GuideBinairoEvery cell is one of two marks.
- GuideStar BattleOne or two stars in every row, column and region.
- GuideSlitherlinkDraw one loop. Start from the 0s and the 3s.
- GuideHitoriShade repeats, never side by side, keep white connected.
- GuideNurikabeGrow each island to its number and keep one sea.
- GuideLight UpLight every cell. Start beside the 4s and 0s.
- GuideKakuroOne-way sums first, then short runs.
- GuideKiller SudokuCage sums, then the rest of the line.
- GuideJigsaw SudokuFollow the thick walls. Each region has its own shape.
- GuideFutoshikiLess-than and greater-than signs between neighbours.
- GuideRenzokuDots between cells. An empty gap means not one apart.
- GuideSkyscrapersEach clue counts the heights it can see.
- GuideCalcudokuOne-way cages first, then the rest of the line.
- GuideShikakuEach number is an area. Start with the ones that fit one way.
- GuideMasyuTurn on black pearls, go straight through white ones.