Shikaku (also called Rectangles or Divide by Squares) is a logic puzzle played on a rectangular grid. Some cells contain numbers. The goal is to divide the entire grid into non-overlapping rectangles (or squares) so that each rectangle contains exactly one number, and that number equals the area of the rectangle.

How do you solve a Shikaku puzzle?

Start with numbers that have only one possible rectangle shape and placement (e.g. a '2' in a corner can only form a 1×2 rectangle in one direction). Then look for numbers whose possible rectangles are constrained by already-placed rectangles or grid edges. Work through eliminating impossible placements until every cell belongs to exactly one rectangle.

What grid sizes are available?

Five sizes: 5×5, 7×7, 9×9, 11×11, and 14×14. Smaller grids are quick and beginner-friendly, while larger grids require more complex spatial reasoning.

What difficulty levels are there?

Three levels: Easy (many small rectangles, straightforward placements), Medium (a mix of small and larger rectangles with more ambiguity), and Hard (larger rectangles and fewer constraints requiring advanced elimination). All puzzles have exactly one solution.

Can rectangles be squares?

Yes. A square is a special case of a rectangle. A cell containing the number 4 could be covered by a 1×4, 4×1, or 2×2 rectangle, for example.

Play Shikaku Online

Divide the grid into rectangles. Each rectangle contains exactly one number equal to its area. Five grid sizes and three difficulty levels — all puzzles have a unique solution.

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Click & drag to draw a rectangle

What Is Shikaku?

Shikaku (四角, literally “four corners”) is a logic puzzle invented by Nikoli, the Japanese publisher famous for popularising Sudoku. It first appeared in 1989 under the name “Divide by Squares” and is also known as Rectangles in English-language puzzle books.

The puzzle is played on a rectangular grid where some cells contain numbers. Your task is to partition the entire grid into non-overlapping rectangles (or squares) such that each rectangle contains exactly one number, and that number equals the rectangle’s area. Every cell must belong to exactly one rectangle.

Rules of Shikaku

Cover every cell: The entire grid must be divided into rectangles with no gaps and no overlaps.
One number per rectangle: Each rectangle must contain exactly one of the given numbers.
Number equals area: The number inside a rectangle must equal the rectangle’s total number of cells (width × height).
Rectangles only: All regions must be rectangular (including squares). No L-shapes, T-shapes, or irregular polygons.

How to Solve Shikaku — Strategy Tips

1. Start With Forced Placements

Look for numbers that can only form one possible rectangle. A 1 always covers just its own cell. A 2 in a corner can only extend in one of two directions. Prime numbers like 3, 5, or 7 can only form 1×N or N×1 rectangles, which greatly limits their placement.

2. Use Edge and Corner Constraints

Rectangles near the edges of the grid have fewer possible orientations. If a number is on the border, any rectangle containing it must fit within the available space. Corner numbers are the most constrained and are often the best starting points.

3. Factor the Number

A number like 6 could be 1×6, 6×1, 2×3, or 3×2. Think about which factorisation fits the available space. Numbers with many factors (like 12 or 16) offer more possibilities and are usually harder to place — solve the constrained numbers first.

4. Fill Remaining Gaps

As you place rectangles, watch for cells that become isolated in small regions. If a region of empty cells can only be covered by one rectangle configuration, that placement is forced. This “fill the gap” technique often chains into solving large areas quickly.

5. Check for Contradictions

If all possible rectangles for a number would overlap with an already-placed rectangle or leave unreachable cells, something is wrong. Backtrack and reconsider your earlier placements.

Grid Sizes

5×5: Tiny, tutorial-level. Ideal for learning the rules. Most puzzles solve in under a minute.
7×7: Small but satisfying. Requires a few careful deductions. Good for quick games.
9×9: Medium. Multiple rectangle sizes interact, and you need to plan ahead.
11×11: Large. Significant spatial reasoning required. Expect 10–20 minutes on harder difficulties.
14×14: Expert. Dense puzzles with many overlapping possibilities. A real challenge even for experienced solvers.

Difficulty Levels

Easy: Mostly small rectangles (areas 1–4). Many forced placements are immediately visible.
Medium: A mix of small and medium rectangles (areas up to 6–8). Requires counting, factoring, and some elimination.
Hard: Includes large rectangles (areas up to 10+). Fewer obvious starting moves; advanced elimination and gap-filling needed.

Shikaku vs Similar Puzzles

vs Sudoku: Both are grid-based logic puzzles, but Sudoku fills numbers into cells while Shikaku partitions the grid into regions.
vs Nonograms: Nonograms shade cells to reveal a picture; Shikaku draws rectangles. Both use row/column reasoning.
vs Nurikabe: Nurikabe also partitions the grid, but into irregular “islands” and a connected “sea.” Shikaku requires all regions to be rectangular.
vs Kakuro: Kakuro is an arithmetic crossword. Shikaku is spatial — the challenge is geometry rather than addition.

Frequently Asked Questions

A logic puzzle where you divide a grid into rectangles. Each rectangle contains exactly one number, and that number equals the rectangle’s area. Every cell must be covered with no overlaps.

Start with the most constrained numbers — 1s, primes, and numbers in corners or along edges. Factor each number to determine possible rectangle shapes, then eliminate shapes blocked by other rectangles or grid boundaries. Fill gaps as they appear.

Yes. A square is a valid rectangle. For example, a 4 could be covered by a 2×2 square, a 1×4, or a 4×1 rectangle.

Yes. Every puzzle generated here is verified to have exactly one valid solution using a backtracking solver before it is presented.

The number in a cell tells you the area (number of cells) of the rectangle that covers it. A 6 means the rectangle is 6 cells in total — it could be 1×6, 6×1, 2×3, or 3×2.

More Logic Puzzles

Enjoy Shikaku? Try these other free puzzles:

Nurikabe

Shade cells to form a connected sea around numbered islands.

Nonograms

Reveal pixel art by filling cells from row & column clues.