How to Play Shikaku

Shikaku is played on a rectangular grid dotted with numbered cells. Your job is to divide the whole grid into rectangles so that:

• Each rectangle contains exactly one number.
• That number equals the rectangle's area — its width × height.
• Every cell belongs to exactly one rectangle.
• Rectangles never overlap or leave the grid.

A clue of 6 can become a 1×6, 6×1, 2×3 or 3×2 box. A 1 is always a single cell.

• Drag across cells to draw a rectangle.
• Click a box to remove it.
• Right-click a cell to erase the rectangle there.

A box turns olive when it holds exactly one clue matching its area, and red when the count or size is wrong.

• Primes first. 2, 3, 5, 7, 11… can only be 1×N or N×1, so their shape is nearly forced.
• 1s and 2s. A 1 is fixed; a 2 usually has only one legal direction.
• Edges and corners. Clues near a boundary have fewer places a rectangle can extend.

• Big numbers early. Large clues occupy so much space they often have only one placement that avoids their neighbours.
• Eliminate. As boxes fill in, isolated empty cells can only belong to one remaining clue — follow the chain.
• Solve by constraint, not by reading order. Attack the most-constrained clue on the board, wherever it sits.

• Starter (5×5) — primes and edges are enough.
• Classic (10×10) — the daily size; combine corners and large numbers.
• Hard (15×15) — carve the grid into regions first.
• Expert (20×20) — systematic elimination required.

Every well-formed Shikaku has exactly one solution and is solvable by pure logic. If you feel forced to guess, it means there's a constraint you haven't used yet — step back and re-check the primes, the edges and corners, and any isolated cell that only one clue can reach. That's the whole appeal: no luck, just deduction.

Stuck on a puzzle from elsewhere? Paste it into the solver.

Shikaku (四角に切れ, "divide into squares") was created by Yoshinao Anpuku in 1989 and published by Nikoli — the Tokyo house that made Sudoku famous. In English it also goes by Divide by Squares, Divide by Box, Rectangles and Cell Blocks. In 2026 it reached a whole new audience as the basis for LinkedIn's Patches, so if you arrived from there, the rules above are all you need.