Shikaku: rules and rectangle-solving techniques
In Shikaku, every clue gives the area of a rectangle that must contain that clue — and no other. The whole grid has to be covered with no gaps or overlaps. This guide shows you how to narrow down possible rectangles and solve by deduction before trying a puzzle from the Shikaku library.
Goal of the game
Divide the entire grid into rectangles. Each clue gives the area of the rectangle that must contain it.
Rules
- Every cell belongs to exactly one rectangle: no gaps and no overlaps.
- Rectangle edges follow the grid lines. A square is allowed; an L-shape is not.
- Each rectangle contains exactly one clue, and its area — width × height — must equal that clue.
- The clue can appear anywhere inside its rectangle. A clue of 1 must form a one-cell rectangle.
How to reason from a clue
- For a clue of 6, start by listing the possible dimensions: 1×6, 6×1, 2×3 and 3×2.
- Rule out rectangles that leave the grid, contain another clue or overlap an area already fixed.
- If only one placement remains possible in the available space, that rectangle is forced.
- Do not look only at dimensions: the exact position of the rectangle is often what decides the move.
Useful first deductions
- Start with clues of 1 and clues that have only one possible rectangle.
- For each clue, systematically eliminate placements that leave the grid, include another clue or overlap a confirmed rectangle.
- If an uncovered cell can belong to only one remaining rectangle placement, that rectangle becomes highly constrained. Shared cells across several candidates can also rule out neighbouring placements.
Common mistakes
- Treating the clue as a perimeter or side length: it represents an area.
- Accepting an L-shape or a rectangle containing more than one clue.
- Assuming the clue must sit in a corner of its rectangle.
- Focusing only near the clues and forgetting to check how distant cells can be covered.
Controls
To play, draw a rectangle between two opposite corners, or select those corners one after the other. A clue of 1 can be confirmed with a single tap.
Escape cancels a selection in progress. A new rectangle can replace rectangles it overlaps. Undo reverts the latest change, and Clear all resets the grid after confirmation. Pause, Resume and Check remain available. Hints and revealing the solution count as assistance.
Difficulty
Easy, Medium and Hard are intended to be solved by logical deduction. As difficulty increases, you often need to compare several possible rectangle placements before eliminating them. Expert may require longer chains of reasoning or controlled assumptions.
FAQ
- Is this guide free?
- This guide and its interactive tutorial are free. Explore the rules here, then browse the game library.
- How do I know whether a rectangle is possible?
- Check three things: its area must match the clue, it cannot contain another clue, and it cannot overlap a rectangle that is already confirmed.
- What should I do if I cannot see a move?
- Go back through each clue and eliminate impossible placements. A cell that can be covered by only one remaining option often reveals the next deduction.