Shikaku frequently asked questions

Shikaku is a Japanese logic puzzle published by Nikoli in which you divide a grid into rectangles and squares. Each rectangle must contain exactly one number, and that number equals the rectangle’s area in cells. A correct puzzle has exactly one solution and can be solved by logic alone, without guessing.

Press on a cell and drag to another cell to draw a rectangle between them. A live label shows the size, and the outline turns green when the shape fits a number. Tap any rectangle to erase it, or use the Eraser, Undo and Redo buttons. On a keyboard, move with the arrow keys and press Enter to start and finish a rectangle.

Shikaku (四角) is Japanese for “square” or “four corners”. The full Nikoli name, Shikaku ni Kire (四角に切れ), roughly means “divide by squares” or “cut into rectangles”. In English the puzzle is also called Rectangles, Divide by Squares or Divide by Box.

Yes. Every puzzle is built by our generator and then checked by an exhaustive solver that proves there is exactly one valid way to split the grid. If a candidate puzzle has two solutions, it is rejected or reworked before you ever see it.

Small grids like 5×5 take a minute or two and are ideal for learning. Medium 10×10 and 15×15 puzzles need overlap reasoning, and our hard 20×20 and 25×25 puzzles can take an hour. Easy puzzles on this site are guaranteed to be solvable with only basic deductions.

Yes. Every size, the daily, weekly and monthly challenges, the printable sheets and the online Shikaku solver are free to use, with no account needed. Your progress and statistics are saved in your own browser.

Shikaku was invented by Yoshinao Anpuku, a mathematics student at Kyoto University, and first published by the Japanese puzzle publisher Nikoli in 1989.

Yes. Squares are rectangles, so a 4 can be a 2×2 square, a 9 can be 3×3, and so on.

A 1 is a rectangle of a single cell. It is already solved — on PuzzleShikaku you can tap it to place its 1×1 rectangle.

Yes. Because the rectangles cover every cell exactly once, the numbers in any valid Shikaku always sum to the total number of cells, for example 100 on a 10×10 grid.

No. Every puzzle here has a unique solution that can be reached by deduction. On the hardest puzzles you may reason “if this, then a contradiction”, but that is logic, not luck.

Sudoku asks you to place digits so that rows, columns and boxes contain no repeats. Shikaku asks you to divide a grid into rectangles whose areas match the given numbers. Both come from Nikoli and both have unique, logic-only solutions.

Yes. Deciding whether a general Shikaku grid has a solution has been shown to be NP-complete, which is why large grids can be challenging even for computers without good heuristics.

Yes. Use the Print button on any puzzle, or visit the printable page to build a sheet of up to 12 puzzles in any size and level, with an answer key.

Yes. The free Shikaku solver lets you type the numbers into a grid of any size up to 30×30; it shows the solution and tells you whether it is unique.

Yes. Your rectangles, time and hints are saved in your browser automatically, so you can close the tab and continue later. Statistics and the daily streak are stored locally too.

Yes. Draw rectangles with your finger, tap to erase, and the layout adapts to small screens. It also works with a keyboard and screen reader labels.

Our solver grades each puzzle. Easy puzzles can be solved using only forced options and reachable cells; Medium requires overlap reasoning; Hard needs longer chains of reasoning.

Shikaku exercises logical reasoning, spatial thinking, planning and concentration, and many people find it relaxing. Like other puzzles, it is a fun mental workout rather than a medical treatment.