One Rule
Every rectangle contains exactly one number, and its area equals that number.
One Solution
Every generated board is solvable, and puzzles are picked to have a single solution wherever possible.
Against the Clock
Each stage is timed and every second left over becomes points. Run out of time and the run ends.
What Is Shikaku?
Shikaku is a puzzle about dividing a square grid into rectangles. Some cells carry numbers; every rectangle you draw must contain exactly one number and cover exactly that many cells. No cell may be left empty and rectangles may never overlap. The puzzle was published by the Japanese publisher Nikoli under the name "Shikaku ni kire" — roughly "divide into rectangles" — and English sources also call it Divide by Box or Rectangles.
Unlike Sudoku, the puzzle is not about placing numbers but about dividing area: how many shapes a number can take depends on its divisors. A prime such as 7 can only be 1×7 or 7×1, while 12 allows 1×12, 2×6, 3×4, 4×3, 6×2 and 12×1. That is why solving always starts from the number with the fewest options. This version runs stage by stage: you start on a 5x5 board, move to 6x6 on stage 3 and 7x7 on stage 5, after which puzzles keep the same size but carry fewer numbers and a tighter clock. Points accumulate across stages — the further you go, the higher your score.
How to Play
- The game starts on a 5x5 board. Clearing a stage takes you further: the board becomes 6x6 on stage 3 and 7x7 on stage 5, and the difficulty keeps rising as the number count drops.
- To draw a rectangle, press a cell and drag. When you release, the selected area is placed as a rectangle.
- To delete a rectangle, tap it. Drawing the same rectangle a second time also removes it.
- If a new rectangle overlaps an existing one, the old one is removed automatically — overlaps can never happen.
- Rectangles that hold exactly one number and match its area appear in pastel colours. Rule-breaking ones are drawn with red stripes: no number inside, more than one number, or the wrong area.
- The "Empty" counter shows how many cells are still open and the "regions" counter how many rectangles are correct. When they reach zero and full, the stage is complete.
- Every stage has a time limit that shrinks as you progress (2.5 minutes for 5x5, 4 minutes for the first 7x7 stage, then 10 seconds less each stage down to 2 minutes). If the clock runs out, the run ends.
- When you are stuck, "Hint" places one correct rectangle. You start with 3 hints, gain one every 3 stages and may use at most one per stage. "Clear" empties the board.
- Stage points are the board area × 4 (100 for 5x5, 144 for 6x6, 196 for 7x7) plus 1 point for every second left on the clock. Points accumulate across stages and your total is saved to the leaderboard after each stage.
Solving Method: Start Where Options Are Fewest
- Primes are the way in. Numbers such as 2, 3, 5, 7 and 11 can only form a single row or column (1×n or n×1). That cuts their possible placements dramatically, so look for them first.
- Edges and corners narrow things down. A number against an edge cannot extend past the board, losing half its options; a number in a corner usually fits in exactly one way. Entering the puzzle from the corners almost always pays off.
- Neighbouring numbers limit each other. Since a rectangle may hold only one number, the cells between two numbers can belong to just one of them. Seeing that neighbours cannot "reach across" each other unlocks most steps.
- Ask who can cover a cell. The classic technique works backwards: look at an empty cell and ask which numbers could reach it. If the answer is a single number, that cell belongs to it and you already know part of the rectangle.
- Watch for cells trapped near the edge. As the solution progresses, cells appear that can only be reached from one direction. They usually signal long, thin rectangles (1×5, 1×7) — the placement players miss most often.
- A cell marked 1 stands alone. A number with area 1 covers only its own cell. Closing these immediately also narrows the options for its neighbours — free progress.
- Do not draw where you are unsure. A wrong large rectangle also deletes the correct rectangles underneath it, and rebuilding costs time. Since every remaining second is worth a point, lost time comes straight out of your score.
- Save your hint for the end. You may use only one hint per stage and a new one arrives every 3 stages, so spend it when the clock is genuinely tight rather than at the first difficulty — failing a stage ends the run.
Which Skills Does It Build?
- A feel for factors: Asking "what shapes can this number take" builds the habit of finding divisors instantly. It teaches multiplication as shape rather than recital — a strong maths exercise, especially for children.
- Spatial reasoning: Picturing how an area can be split into rectangles is direct practice in geometric thinking. Rotating and fitting shapes in your head is constantly at work here.
- Constraint-based thinking: The question "who can reach this cell?" is progress by elimination — the same reasoning used from programming to planning.
- Sustained attention: Because the whole board must be covered, a single overlooked empty cell counts as an error. The puzzle trains long, detail-focused concentration.
- Working under time pressure: Each stage is timed, so you have to balance certainty against speed — deciding when to verify and when to commit.
Frequently Asked Questions
Is Shikaku free?
Yes. The game is completely free, needs no sign-up or download and runs straight in your browser.
What is the rule of Shikaku?
You divide the grid into rectangles. Each rectangle must contain exactly one number and cover exactly that many cells. Rectangles cannot overlap and no cell may stay empty.
Where should I start?
With primes (2, 3, 5, 7) and numbers near an edge or corner. They have the fewest placements, so the first certain rectangles usually come from there.
Does every puzzle have one solution?
After generating a board the game counts its solutions and picks one with a single solution. Rarely, when the time budget runs out, a board with more than one solution can appear; in that case any valid division still counts as a win.
How do I delete a rectangle I drew wrong?
Just tap it. Drawing the same rectangle again also removes it, and the "Clear" button empties the whole board.
What does a red striped rectangle mean?
It breaks the rule: it contains no number, more than one number, or its area does not match the number inside. Correct rectangles appear in pastel colours.
How do the stages progress?
You start on a 5x5 board, move to 6x6 on stage 3 and 7x7 on stage 5. The board stays at 7x7 but puzzles keep getting harder because they contain fewer numbers and the clock shrinks each stage. There is no upper limit on stages.
When does a run end?
If you cannot finish a stage within its time limit the run ends and the points you collected become your score. You can also stop after any stage with "Finish and return" — your score is saved either way.
How do hints work?
You start with 3 hints, gain one every 3 stages and can use at most one per stage. Hints cost no points; the limited supply is the cost.
How is the score calculated?
Each stage gives board area × 4 as a base (100 for 5x5, 144 for 6x6, 196 for 7x7) plus 1 point for every second left on the clock. Points accumulate across stages and your total goes to the leaderboard.
Ready to Start?
Press the "Start game" button above and begin right away — no sign-up, completely free.
For more brain training try all our brain games or take the free IQ test.