Play Shikaku Online Free

Nikoli introduced Shikaku in 1989. Its Japanese name refers to dividing by squares, though valid regions may be any axis-aligned rectangles. Each printed number gives the exact area of one rectangle, and the finished partition covers every cell without overlap. The puzzle strengthens factor recognition, spatial planning, and exact-cover reasoning because a clue such as 12 may form 1 by 12, 2 by 6, or 3 by 4 shapes where space permits. Draw a forced rectangle first and partition a Shikaku grid in your browser.

1. Inspect each clue and list factor pairs for its value. A 6 can produce a 1 by 6, 2 by 3, 3 by 2, or 6 by 1 rectangle, although grid edges and nearby clues remove many placements.
2. For each clue, imagine every rectangle of the correct area that contains its cell. Reject any candidate that leaves the board, contains another clue, or crosses a region you have already fixed.
3. Draw a rectangle when only one candidate remains. Its border claims all enclosed cells, and no later rectangle may enter them. Reevaluate neighboring clues against the newly reduced space.
4. Check uncovered cells as well as clues. If an empty cell can belong to only one clue's remaining rectangle, that rectangle must expand to include it. This reverse view often breaks a stall.
5. Finish when nonoverlapping rectangles cover the whole grid. Verify that each contains exactly one clue and that its width multiplied by height equals that clue. No cell may remain outside a border.

• Every region must form one rectangle with horizontal and vertical sides. L-shapes, stepped borders, and disconnected groups never qualify.
• Each rectangle contains exactly one printed number. A shape containing two clues fails even when its area matches one of them.
• A rectangle's area in cells must equal its clue. Multiply width by height; do not count border segments or physical line length.
• Rectangles cannot overlap, and together they must cover every grid cell. Borders may touch, but no cell can belong to two regions.
• The printed clue may sit anywhere inside its rectangle. It does not need to occupy the center, a corner, or any symmetric position.

• Start with prime clues near restrictive edges. A prime area allows only 1 by n or n by 1 shapes. Corners and neighboring clues often eliminate one orientation immediately.
• Mark the intersection of all candidates for a clue. Even when you cannot draw its complete rectangle, cells shared by every candidate definitely belong to it and can block other candidates.
• Watch for stranded cells. Before fixing a rectangle, inspect the pockets it would leave. If an uncovered pocket contains no clue or has too few cells for its clue's smallest feasible rectangle, reject that placement.
• Use area accounting in enclosed spaces. If a section bounded by solved rectangles contains clues totaling exactly its number of cells, those clues cannot extend outside. Conversely, a total that is too small requires at least one region to cross the tentative boundary.
• Search from cells as well as numbers. An edge cell may lie within the reach of only one clue after other regions narrow the board. That ownership can force a rectangle farther than clue-centered analysis alone reveals.

• Aquarium: Aquarium supplies irregular regions and asks you to choose their water levels. Shikaku asks you to discover rectangular regions from area clues. Both reward careful reading of boundaries and cell ownership.
• Dominosa: Dominosa partitions a number grid into fixed 1 by 2 pieces, while Shikaku uses rectangles of many sizes. Both act as exact-cover puzzles in which every cell belongs to one region.

• The objective stays visible. Every border adds a recognizable piece to the final partition, and players can verify its area immediately.
• Factor pairs turn arithmetic into geometry. The same clue behaves differently near a corner, beside another number, or inside a narrow unsolved channel.
• Several reasoning directions remain available. Players can study clue candidates, uncovered cells, enclosed areas, or stranded pockets, which keeps a difficult grid moving without random trial.

Play Shikaku online for free and draw rectangular borders directly on the grid. The interface keeps clue positions visible and makes resizing or removing a tentative region quick. Begin with small clues and edge restrictions, then use the solved borders to narrow larger factor pairs. Easy boards teach area matching in minutes, while harder boards demand exact coverage planning across wider open spaces.

Shikaku has appeared in Nikoli publications since 1989, yet its central rule remains compact: one clue, one rectangle, exact area. List factor pairs, remove placements that hit other clues, and protect every cell from becoming stranded. The best deductions often come from the space around a number rather than the number itself. Start a grid above, draw the rectangle with one legal placement, and let its border organize the rest of the partition.

• Shikaku rules (Nikoli)