Shikaku Puzzles
A grid divided into rectangles, and every rectangle carries exactly one number: its own area. Nothing is hidden — every number is shown from the start. The puzzle is finding where each rectangle's edges actually fall. Tap one corner of a rectangle, then tap the opposite corner, and it locks in if it holds exactly one number and matches its area.
Also called rectangles or divide by box.
Related Practice
What Is A Shikaku Puzzle?
Shikaku — Japanese for "four corners" — is a grid divided entirely into rectangles, where every rectangle contains exactly one number, and that number is the rectangle's own area in cells. Nothing else is given: no clue is ever removed, because the whole puzzle is finding the boundaries, not finding the numbers. A 6 could be a 1×6 strip, a 2×3 block or a 3×2 block — the grid tells you which, once the rectangles around it are pinned down.
It is also published as Rectangles and Divide by Box, and — like nurikabe and heyawake, both also on this site — was popularised by the Japanese puzzle magazine Nikoli. The rule set is short enough to state in one sentence: divide the grid into rectangles so that every rectangle holds exactly one number, equal to its area.
Every Rectangle Is Drawn, Not Typed
Tap one corner of the rectangle you intend, then tap the opposite corner. The board checks three things before it locks the shape in: that it holds exactly one number, that its area matches that number, and that it does not cover a cell some other rectangle already owns. Fail any of those and nothing is placed — the board tells you which rule stopped it.
A shape that passes those three checks is still allowed to be wrong. Shikaku is exactly like sudoku in this respect: a locally legal placement can still lead the rest of the grid into a dead end. Tapping any cell of a placed rectangle removes it again, so a wrong guess costs one undo, not a restart.
Why Every Number Is Always Shown
Every other shading puzzle on this site strips clues for difficulty — heyawake hides most of its room numbers, nurikabe removes what it can before the grid stops being solvable without guessing. Shikaku cannot: the numbers ARE the puzzle. Take one away and its rectangle's area is simply unknown, which is not a harder puzzle, it is an unsolved one. Difficulty here comes from the grid instead — its size, and how large the rectangles are allowed to grow, which changes how many candidate shapes a number has before one is forced.
Built From The Rectangles, Not Discovered In Them
Shikaku is built the same way this site's heyawake rooms are (§ heyawake's own page): the grid is cut into rectangles FIRST, by the same recursive guillotine-cut construction, and one number is read out of each — so a valid tiling exists before a single clue is chosen. What has to be checked afterward is whether that clue SET still points back to only one tiling, which a deduction pass proves directly: if every number narrows to exactly one legal rectangle without ever guessing, no other tiling could produce the same numbers, so the one found is the only one. A grid that cannot be finished this way is never shown.
Rectangles as small as a single cell are always allowed on purpose. A lone "1" needs no deduction at all — it is trivially its own whole rectangle — and having a few of those in a grid was measured to make the REST of the grid dramatically easier to pin down too, since a settled cell rules out candidate shapes for everything around it.
Shikaku Puzzles Frequently Asked Questions
What is a shikaku puzzle?
A grid divided entirely into rectangles, where every rectangle holds exactly one number equal to its own area. Every number is shown from the start; the puzzle is finding where each rectangle's edges fall.
Why are all the numbers given, unlike your other shading puzzles?
Because the number IS the clue about the shape, not a fact to be worked out. Removing one would leave a rectangle with an unknown area, which breaks the puzzle rather than making it harder. Difficulty instead comes from grid size and rectangle size.
What is the best way to solve a shikaku puzzle?
Start with any 1 — it is already its own rectangle. Then look for numbers boxed in by their neighbours, since they often have only one legal shape left. Every rectangle you place rules out candidate shapes for the numbers around it, which is usually what forces the next one.
Can a rectangle contain more than one number?
No — every rectangle in a valid solution holds exactly one number, and that number always equals its area. The board refuses a shape covering two numbers, or one whose area does not match.
Is shikaku the same as Rectangles or Divide by Box?
Yes — those are two other published names for the identical rule set. Shikaku is the Japanese name and the one most puzzle sites use.
Is it free, and does it need an account?
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