Thermometers is a free online thermometer puzzle. The grid is cut into glass thermometers, each with a round bulb at one end, and the numbers beside the rows and above the columns say how many squares in that line hold mercury. Mercury always starts in the bulb and rises along the tube without gaps, so a thermometer can be empty, full, or filled part of the way, but never in pieces. Work out how far each one is filled. Tap a square to fill its thermometer up to it, tap the top again to let one square drain, or drag across the board to fill several at once; cross out squares you know stay empty. A number turns red when its line holds too many. The first levels use straight tubes; from level 5 the tubes bend round corners. Every board is generated by the game, has exactly one answer, and is proved solvable by reasoning alone before you see it. Eight levels run from a 5×5 grid to a 10×10. No download, no account.
How to play Thermometers
- The grid is cut into thermometers. Each has a round bulb at one end and a tube that runs from it in a straight line or, from level 5, round corners.
- Mercury fills a thermometer from its bulb towards the other end without gaps. A thermometer can be empty, full or filled part way, but a filled square always has every square between it and the bulb filled too.
- The number beside each row and above each column is how many of that line's squares are filled. Fill the thermometers so every number comes true.
- Tap a square to fill its thermometer up to that square. Tap the top filled square again to drain it, or tap lower down to drop the mercury there. Drag from an empty square to fill several squares at once, or from a filled one to drain them.
- Right-click a square, press X, or switch on ✕ Mark and tap, to cross it out as a reminder that it stays empty. Crossing out a filled square drains its thermometer down to just below the cross; tapping a crossed square clears the cross.
- A number turns red when its line already holds more filled squares than it asks for, and green when it holds exactly that many.
- The board is solved the moment every row and column total is met. Undo steps back one change, Clear empties the board, and New Puzzle deals another board on the same level.
- The ? button settles one square: mercury above the answer is drained first, otherwise it fills or crosses out the next square the reasoning reaches. Three per board.
Tips
- Start with the zeros and the full lines. A 0 empties every square in its line, and a number as big as the line fills every square — and filling a square fills everything between it and its bulb.
- A bulb sitting in a 0 line means that whole thermometer is empty, wherever its tube goes.
- A square near the tip of a long tube is the last to fill. If a line needs only one more square, it cannot come from the middle of a thermometer lying along that line unless everything below it in the tube is filled too.
- Count what a line can still get. When a row needs four more and the other tubes crossing it can give at most two, the long tube lying along that row must give the other two — from its bulb end.
- Cross out the squares you know stay empty; on a big board they are what lets you see which tubes still have room.
- On the last three levels, try one square in your head. If filling it makes some row or column impossible, it stays empty; if leaving it empty does, it is filled.
FAQ
Is Thermometers free to play?
Yes. It runs in the browser with no download, no sign-up and nothing to buy. All eight levels are included and unlock as you solve them, and New Puzzle deals more boards on any level you have reached.
What are the rules of the Thermometers puzzle?
Fill some of the thermometers with mercury, starting from the bulb and going towards the end without gaps. The numbers outside the grid give how many squares are filled in each row and each column. Find the one way to fill them that matches every number.
Can a thermometer be completely empty, or completely full?
Yes, both. A thermometer may be filled to any level from nothing at all to every square. What it can never be is filled in pieces: the mercury always starts in the bulb and every filled square has the squares between it and the bulb filled too.
What is the difference between straight and bent thermometers?
Only the shape. Levels 1 to 4 use straight tubes; from level 5 the tubes can turn corners, so one thermometer can pass through several rows and columns at once. The rule is the same: mercury runs from the bulb along the tube.
Does every puzzle have exactly one answer?
Yes, and it is checked rather than assumed. Each board is built from a real filling, and a program that only makes forced deductions — no guessing — must finish it before it is shown; a board it can finish that way has only one answer. The tests confirm it with an exhaustive search as well.
Will I ever have to guess?
No. Levels 1 and 2 need only counting: a line whose number is already met empties the rest, and a line that needs every open square fills them. Levels 3 to 5 also need a thermometer lying along a line: when the rest of the line cannot give enough, that tube must give the rest, from its bulb end. Levels 6 to 8 each need "what if" steps — one or two on level 6, two to five on level 7, and four or more on the 10×10.
How is this different from Nonogram or Battleships?
All three use numbers beside the rows and columns. In a Nonogram the numbers describe runs of shaded squares, and in Battleships they count pieces of hidden ships. In Thermometers they count filled squares, and the shapes are already drawn: what you decide is how far each thermometer is filled.
How many levels are there?
Eight, from a 5×5 grid to a 10×10. Each level's boards are built fresh from a seed, so Replay gives the same board again and New Puzzle a different one at the same difficulty.
Does Thermometers work on a phone?
Yes. Tap or drag with a finger to fill, and switch on ✕ Mark to cross squares out by tapping. On a phone held upright the board fills the screen's width; held sideways, the buttons move beside it.