Thermometers Logic Puzzle
Fill each thermometer from the bulb. Pick Fill or Cross, then fill each thermometer from the bulb so the outside numbers match.
Tap to fill from the bulb up to a cell. Tap again to clear. M switches mode.
How to play Thermometers
Choose Fill or Cross
Fill is a mercury bar. Cross is a ×. Tap a cell, or drag along a tube, to apply that mark. 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. Cross marks that cell and every cell toward the tip. Tap a cross again to clear that stretch. There is no tap that cycles a cell through empty, fill, and cross.
Match the outside numbers
A number beside each row and above each column says how many cells in that line hold mercury. Zero is a real clue and means the line is empty. Mercury is one bar from the bulb, with no gap. A cross means you know the cell is empty. The tubes and the numbers are printed on the grid and stay put.
Finish the mercury
The puzzle is finished when the filled cells are the one solution and the outside numbers match. Crosses are optional. An empty cell counts as not mercury, so you can solve with fills alone. A gap, or a line whose count cannot be met, is a mistake.
Thermometers is a logic puzzle about filling straight tubes from the bulb. Numbers outside the grid say how much mercury each row and each column holds. You can play grids from 6×6 up to 10×10, and every puzzle here has exactly one mercury pattern that you can reach by logic, with no guessing. People also look this up as a thermometer puzzle, a thermometers logic puzzle, or a printable thermometers puzzle.
Rules
The board is an n×n grid. Straight tubes cover every cell. One end of each tube is a round bulb. A number above each column and beside each row says how many cells in that line are filled. Zero is a real clue.
Mercury starts at the bulb and runs toward the tip as one bar. It does not jump over an empty cell or a cross. A cross is a cell you have marked as empty. The tubes and the numbers are given. You do not move them.
The puzzle is solved when the filled cells are the one solution. Crosses are not required. A cell you have not marked counts as not mercury.
Controls
Choose Fill or Cross under the board. Tap a cell to apply that mark. Fill sets the mercury from the bulb up to the cell. Tap the cell that is currently the surface of the mercury to lower the level by one. Cross marks the cell you touch and every cell from there to the tip. Tap a cell that already has a cross to clear that stretch back to empty.
A drag follows the tube. Fill sets the level to the furthest cell you crossed, and it does not lower the level when the stroke visits several cells. Cross 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.
On a keyboard, the arrow keys move around the grid. Space or Enter applies the selected mark. F or 1 fills to the cell. 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.
A cell or an outside number turns red when mercury has a gap, or when a row or column count is already too high or can no longer be met. Press Hint for one step the rules already force, with a sentence saying why. Press Check when you want the board checked against the rules. Undo and Redo step through your moves, and Reset clears the marks you placed. The tubes and the numbers stay. When the mercury matches, the board turns teal.
Techniques
Easy grids follow from one line:
- Zero line: a line numbered 0 is empty, so each thermometer that meets it stays empty from that cell to the tip.
- Full line: a line that is already full is filled back to the bulb.
- Rest empty: a line that already has its count leaves the remaining cells empty.
- Rest fill: the open cells on a line are exactly the mercury still needed, so they are filled.
- Too long: mercury past this cell would pass the line’s count.
- Must stem: the line cannot reach its count unless the mercury gets this far.
Beginner tips
Start with the zeros. A 0 clears every tube that touches that line, from the meeting cell out to the tip. Then look for a line whose number equals its length, and fill those tubes back to the bulb. If a line already has enough mercury, cross the rest. If the unmarked cells are exactly the count you still need, fill them, including the stem back to the bulb.