How to play Shikaku

You are dividing a grid into rectangles. There are only three rules, but each placement changes what is possible around it.

1. Every rectangle has exactly one number. Empty rectangles and rectangles containing two clues are not allowed.
2. The number equals the rectangle’s area. A 6 needs six cells, for example three columns by two rows. The clue can sit anywhere inside its rectangle.
3. Cover the entire grid without overlaps. Rectangles meet at edges. A cell cannot belong to two of them.

Area, not side length

3 across × 2 down = 6 cells

A 4 could form a 1 × 4 strip, a 2 × 2 square, or a 4 × 1 strip. A square is a valid rectangle. An L-shape covering four cells is not. A 1 takes just its own cell.

A small worked example

Start with the 4 in the top-left corner. A horizontal strip would cross the 2 in row 1. A vertical strip would cross the 3 in column 1. Only its 2 × 2 square fits. You have found a forced move without guessing.

Now consider the 2 at row 1, column 3. Going down would include the next 2, and going left would overlap the 4. It must extend right. The other 2 in row 2 then fills the two cells directly below it.

The 3 in row 3, column 1 cannot be vertical on this 4-row board. It fills the first three cells of row 3. The bottom-row 3 covers the first three cells of row 4; the remaining 2 stands vertically at the right edge.

Playing on Shikaku Grove

Tap a cell to mark the first corner, then tap the opposite corner. You can also drag from corner to corner. A legal move fills the rectangle. Drawing a new rectangle for the same clue replaces its old one if it does not overlap another region.

Undo takes back a move. Erase switches to removal mode: select a filled region to clear it, then switch Erase off to draw again. Explain a step shows a reason you can check on the board; you choose whether to place its suggested rectangle.

Keyboard controls: use the arrows to move, Enter or Space to choose corners, Escape to cancel a selection, and Delete or Backspace to remove a rectangle. Your progress is saved locally when storage is available. The timer pauses when the page is hidden.