Shikaku rules in one sentence: divide the grid into rectangles (or squares) so that every rectangle contains exactly one number and that number equals the number of cells in the rectangle.
The rules of Shikaku
- Cover the whole grid. Every cell belongs to exactly one rectangle. There are no gaps and no overlaps.
- One number per rectangle. Each rectangle contains exactly one of the given numbers.
- Area equals the number. A rectangle containing a 4 covers exactly four cells: 1×4, 4×1 or 2×2.
Squares are rectangles too, so a 9 may be a 3×3 square. A 1 is a single cell on its own. Shapes must be true rectangles — no L-shapes, no T-shapes.
A worked example
Here is a 5×5 Shikaku. The numbers add up to 25, the number of cells. Try to solve it in your head before looking at the solution on the right.
Notice how every coloured rectangle holds one number and has exactly that many cells. There is no other way to split this grid that follows all three rules — every puzzle on PuzzleShikaku is checked by computer to make sure of this.
Valid and invalid shapes
Controls on PuzzleShikaku
| Action | Mouse / touch | Keyboard |
|---|---|---|
| Draw a rectangle | Press and drag from one corner to the opposite corner | Arrow keys to move, Enter to start, move, Enter to finish |
| Erase a rectangle | Tap/click it, right-click, or use the Eraser tool | Delete or Backspace |
| Undo / redo | Undo and Redo buttons | Ctrl+Z / Ctrl+Y |
| Hint | Hint button | H |
| Pause | Pause button | P |
| New puzzle | New puzzle button | N |
Drawing over existing rectangles replaces them, so you rarely need to erase first. Turn on Highlight mistakes if you want instant feedback on rectangles that are not part of the solution.
Your first moves
- Start with the biggest number or a number in a corner — they have the fewest possible shapes.
- Prime numbers (2, 3, 5, 7, 11, 13…) can only be straight 1-wide strips.
- Look at empty corners. Ask which numbers could possibly reach that cell. If only one can, it must.
Every technique is explained step by step, with diagrams, in the Shikaku strategy guide.
What next?
Try a 5×5 puzzle to practise, then move up to 10×10. When you are ready, the Daily Shikaku gives you a new puzzle every day.
Ready to try it?
Start with an easy 5×5 grid — most people solve their first one in under two minutes.