Puzzle Royale
How to play Shikaku
Split the grid into rectangles
Also known as Divide by Box, Rectangles.
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Cover the grid
Split the whole grid into non-overlapping rectangles, one per number — cover every cell and the puzzle is solved.
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Drag to draw a rectangle
Press a cell and drag to the opposite corner, then release to place a rectangle. A correct one turns green and locks — tap it to remove it if you want to redraw.
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Each number is an area
Every rectangle holds exactly one number, and that number is how many cells it covers — a 6 means six cells.
Play Shikaku now
Solving tips
- Primes first: a prime-number clue can only be a 1-wide strip — just two orientations to test.
- Big numbers next: large areas have few legal placements, so they’re often forced.
- Claim orphan cells: a cell only one clue can possibly reach must belong to that clue’s rectangle.
- Slide the shape: mentally slide each possible rectangle around its clue — any cell covered by every placement is certain.
- Square numbers (4, 9, 16) aren’t always squares — check the strip shapes too.
Where Shikaku comes from
- Invented in 1989 by Yoshinao Anpuku, then a mathematics student, and published by Nikoli.
- The name is short for "shikaku ni kire" — Japanese for "cut into rectangles!".
- Published around the world as Cell Blocks (The Times), Divide by Box, and Rectangles — it also runs in The Wall Street Journal.
- NP-complete: deciding whether an arbitrary Shikaku grid has a solution is provably hard.
- Built-in bookkeeping: the clue numbers always sum to exactly the grid’s area — every cell belongs to exactly one rectangle.
Play it against a hundred other solvers
Puzzle Royale wraps Shikaku and seven other logic puzzles in a battle
royale: a hundred solvers enter, four rounds, half the field goes out each time,
one champion. Or play it untimed in Practice with no stakes at all.
Try a Shikaku puzzle
The other seven