How to Play Shikaku

A complete guide to rules, controls, and solving techniques.

The Goal

Divide the entire grid into non-overlapping rectangles. Each rectangle must contain exactly one clue number, and the rectangle's area must equal that number.

That's the whole game. Simple to state, but the puzzles can require deep logical thinking to solve — especially at higher difficulties where multiple constraints interact.

The Rules in Detail

Rule 1: Cover every cell

Every cell in the grid must belong to exactly one rectangle when the puzzle is solved. No cells left over, no cells in two rectangles at once.

Rule 2: One clue per rectangle

Each rectangle contains exactly one number (the clue). If a rectangle would contain zero or two clues, it's invalid.

Rule 3: Area must match the clue

If a clue says 6, the rectangle it belongs to must have an area of exactly 6 cells. That could be a 1×6, 6×1, 2×3, or 3×2 rectangle — all are valid as long as the area is 6.

Rule 4: Only rectangles (no L-shapes)

Shikaku only allows axis-aligned rectangles. You cannot place an L-shaped region, a diagonal line, or any other irregular shape.

A Simple Example

This 4×4 puzzle has one valid solution. Compare the starting clues with the completed rectangle layout:

Starting puzzle

Unique solution

Working through it:

The two 2 clues in the upper-right cannot extend vertically because that would put both clues in one rectangle. Each must extend horizontally across its row.
The top-left 4 then fills the remaining 2×2 space in the upper-left.
The lower-left 2 extends vertically through the two remaining cells in its column.
The 6 covers the final 2×3 area. All 16 cells are covered, with exactly one matching clue in every rectangle.

Every Shikaku puzzle generated on this site has a unique solution — there is always exactly one correct arrangement.

Controls

Mouse / Touch

Drag across the grid to draw a rectangle. While dragging, a dashed outline shows your current selection.
A green outline means the placement is valid (one clue inside, area matches, no overlap).
A red outline means the placement is invalid.
Release to place the rectangle (green only; red placements are rejected).
Click an existing rectangle to select it. A selected rectangle shows a highlight border.
With a rectangle selected, click the Delete button in the toolbar (or press Delete) to remove it.
On larger boards, use −, +, or Fit to adjust the board size.
On touchscreens, use two fingers to pinch-zoom and pan. One finger or a stylus continues to draw rectangles.

Prefer tapping? Open Preferences and choose Tap two corners. Tap one corner, then its opposite corner. For large boards, use the zoom controls and Move board to pan without drawing.

Keyboard

Key	Action
`Arrows`	Move around the board or extend a rectangle
`Enter` / `Space`	Start or place a rectangle; select an existing rectangle
`Ctrl`/`Cmd`+`Z`	Undo the last placement or deletion
`Ctrl`+`Y`	Redo
`Delete` / `Backspace`	Remove the selected rectangle
`Escape`	Cancel current drag / deselect

The Toolbar

Below the grid, the action bar provides:

Undo / Redo — Step backward and forward through your move history. There's no penalty for undoing.
Delete — Remove the currently selected rectangle.
More → Restart puzzle — Clear all your placed rectangles and start the current puzzle over.
Hint — Get a hint that suggests or reveals part of the solution. Each hint is counted and shown in your stats.
More → Achievements — View your earned achievements and progress.
More → How to play — Quick reference for rules and controls (you're reading the full version now).

The Hint System

If you're stuck, choose Hint for a nudge, then Explain for guidance. When a rectangle is proven, Reveal rectangle lets you place it. Hints are tracked and displayed in your completion stats, so you can aim for hint-free solves as a personal challenge.

Hints do not unlock automatically — you choose when to use them. There's no limit, so use as many as you need while learning.

Difficulty Levels

Difficulty	Grid Size	Scale of Play
Easy	5–7 squares wide	Small boards for learning and quick sessions
Medium	7–9 squares wide	More space to explore rectangle shapes
Hard	9–12 squares wide	Larger boards with more possibilities to track
Extreme	12–14 squares wide	A substantial board for a longer session
Expert 3 free samples	15–17 squares wide	Large grids with deep interdependencies
Insane Unlock	18–20 squares wide	Very large; requires tracking many possibilities simultaneously
Nightmare Unlock	21–24 squares wide	The largest boards in the collection

Solving Strategies

See the full Shikaku Strategy Guide for in-depth techniques. The short version:

Start with small clues. A clue of "1" is always a 1×1 square. A clue of "2" can only be 1×2 or 2×1. Resolve these first.
Work the corners and edges. Clues near corners have far fewer valid rectangle orientations, making them the easiest to pin down.
Eliminate by area. If a clue is 12 and the only rectangles that fit are 3×4 and 4×3, you know which cells must be inside that rectangle regardless of orientation — the intersection of both options is committed.
Look for cells with only one possible owner. If only one clue's candidates cover a particular cell, that clue must own it.

Completion and Stats

When you correctly place rectangles covering every cell of the grid, the puzzle is solved. A completion screen shows:

Your solve time
Move count (each rectangle placed or removed counts as one move)
Hints used
Whether you set a personal best time for that puzzle

Best times are saved locally in your browser and persist across sessions.

Progress and Session Restore

Your current puzzle progress is saved automatically as you play. If you close the tab or browser and return later, your progress is restored — no account or login needed. All data stays in your browser's local storage.