Play Shikaku Online — Free
The Japanese rectangle puzzle: divide the grid into boxes so each number sits in a rectangle of exactly that area. Unlimited puzzles, three sizes, and every board is machine-checked to have exactly one solution.
What is Shikaku?
Shikaku (四角, "square" or "rectangle"), also published as Divide by Squares and Divide by Box, is a Japanese logic puzzle built on a single rule: split the whole grid into rectangles so that each rectangle contains exactly one number, and its area equals that number. A 6 must live inside a 1×6 or 2×3 box; a 9 inside a 1×9 or 3×3; every cell of the grid must end up inside exactly one box. Nothing overlaps, nothing is left over.
Like the best of the Japanese deduction family — Nurikabe, Slitherlink, Hitori, Kakuro — the rule fits in one sentence, and the depth comes from geometry rather than arithmetic. Prime numbers can only stretch into thin strips; corner clues have two directions instead of four; and because every cell must be claimed by someone, an awkward gap that only one clue can reach settles that clue instantly. Every puzzle served here is generated fresh and then verified by a solver that counts solutions, so exactly one arrangement works and pure logic is always enough — no guessing, ever.
How to Play
Shikaku Tips & Strategy
Shikaku rewards knowing where certainty hides. These four habits find it fastest.
Primes first
A prime clue — 2, 3, 5, 7 — can only form a strip 1 cell wide, so it has at most two orientations. On the edge of the board, often only one fits. Lock the primes early and the flexible clues around them lose most of their options.
Corners and edges are half-solved
A clue in a corner can only grow in two directions, an edge clue in three. Combine that with the shape catalogue of its number and many border clues have exactly one legal rectangle before you have placed anything at all.
Every cell needs an owner
The most powerful deduction is not about a clue — it is about an empty cell. List which clues could possibly reach a lonely cell; if only one can, that clue's rectangle must cover it, which usually fixes its shape completely.
Sketch the possibilities of big squares
Composite numbers like 12 or 16 have several shapes (1×12, 2×6, 3×4 …), but each must still contain its clue and avoid other numbers. Rule out shapes that would swallow a second clue — a rectangle may contain exactly one number, so most large shapes die quickly.
Guaranteed Unique Solutions
A logic puzzle is only as good as its guarantee. Some generators ship boards with multiple solutions, which silently turns deduction into guessing — you can be "wrong" while following the rules perfectly. This page refuses to do that: after generating a candidate board, a backtracking solver counts its solutions, and the board is discarded unless the count is exactly one. What reaches your screen is always solvable by chains of certainty, from the first prime to the last awkward gap.
The three sizes are honest difficulty steps rather than artificial limits. A 5×5 board teaches the shape catalogue in a minute or two; 7×7 introduces longer chains where an edge deduction unlocks the middle; 10×10 boards hold twenty-plus clues whose possibilities genuinely interlock. If you enjoy the partitioning style, its closest relatives on vygam are Nonogram for picture logic, Binairo for row-balance logic, and Futoshiki for inequality chains.
FAQ
Is Shikaku free to play?
Yes — Shikaku on vygam is completely free with unlimited puzzles. There is no download, no sign-up and no daily cap; finish one board and generate the next instantly.
How do you play Shikaku?
Divide the whole grid into rectangles. Each rectangle must contain exactly one number, and its area must equal that number — a 6 becomes a 2×3 or 1×6 box around that clue. When every cell belongs to a valid rectangle, the puzzle is solved.
Does every puzzle have exactly one solution?
Yes. Every board on this page is generated and then machine-checked by a solver that counts solutions — a puzzle is only served if exactly one solution exists, so pure logic always suffices and guessing is never required.
What do the numbers mean?
Each number states the exact area of the rectangle that must contain it. A 4 can be 1×4, 4×1 or 2×2; a 7 (prime) can only be 1×7 or 7×1 — prime clues are the most constrained and usually the best place to start.
What is a good Shikaku strategy?
Start with primes and large numbers, whose shapes are most restricted, and with clues near edges and corners, which have fewer directions to grow. Every cell must be covered, so a cell reachable by only one clue's possible rectangles decides that rectangle immediately.
What is the difference between the difficulty levels?
Board size: Easy is 5×5, Medium 7×7 and Hard 10×10. Bigger boards mean more clues, more overlapping possibilities and longer deduction chains, but the rules never change.
Is Shikaku related to Sudoku?
They are cousins from the same Japanese logic-puzzle tradition and share the one-rule, pure-deduction spirit, but they exercise different muscles: Sudoku is about placing symbols under constraints, Shikaku is about partitioning space by area — closer to Nurikabe or Slitherlink than to Sudoku.