What is a Shikaku solver?
A Shikaku solver is an online tool that completes a Shikaku rectangle puzzle from its numbered area clues. Shikaku, also called Divide by Squares or Divide by Rectangles, asks you to partition the whole grid into rectangles.
Each rectangle must contain exactly one number, and that number must equal the rectangle's area. This page is built for searches such as Shikaku solver, Shikaku puzzle solver, online Shikaku solver, free Shikaku solver, Shikaku helper, Shikaku answers, Shikaku hints, Shikaku strategy and how to solve Shikaku.
- Solve a Shikaku puzzle from a book, app, newspaper or printable sheet.
- Enter the numbered area clues directly on the grid.
- Check whether a Shikaku puzzle has no solution, one solution or multiple solutions.
- Reveal one logical rectangle without showing the entire answer.
How to use this Shikaku solver
Choose a grid size, then click Create grid. Click a cell and type the clue number printed in your puzzle. Backspace or Delete clears the selected clue.
Press Solve to complete the rectangle division. Press Check if you only want to know whether the clue set is valid. Press Next move for a single highlighted rectangle, then Apply move if you want to add it to the board.
- Use the grid exactly as the puzzle is printed.
- Leave blank cells empty.
- The sum of all clue numbers must equal the total number of cells.
- Start with the examples if you want to see the input format.
- Clear rectangles keeps your clues and removes only the solved regions.
Shikaku rules used by the solver
The solver follows the standard Shikaku rules. The full grid must be divided into non-overlapping rectangles, and every cell must belong to exactly one rectangle.
Every rectangle contains one clue only. A clue of 12 could be 1x12, 2x6, 3x4, 4x3, 6x2 or 12x1 if the shape fits inside the board and does not include another clue.
- Each rectangle contains exactly one numbered clue.
- The rectangle area equals the clue number.
- Rectangles may be long, wide or square.
- Rectangles cannot overlap.
- A solved Shikaku grid has no empty cells and no gaps.
Next move logic and Shikaku strategy
The Next move button starts with the most natural Shikaku deduction: a clue whose possible rectangles have been reduced to one. Corners, edges, small numbers and prime numbers often create these forced rectangles.
If no single clue is locally forced, the helper searches valid completions and looks for a rectangle that every solution agrees on. That gives a useful Shikaku hint while still revealing only one move.
- List the factor pairs for each clue.
- Remove rectangles that would cover another clue.
- Use edges and corners to reduce possible placements.
- Watch whether a rectangle would leave an uncovered space with no clue.
- When all solutions share one rectangle, that rectangle is forced.
Why a Shikaku puzzle can be impossible or ambiguous
A Shikaku puzzle is impossible when the clue areas do not match the grid area, a clue has no rectangle that can fit, or every possible rectangle arrangement leaves an overlap or a gap.
A puzzle is ambiguous when more than one rectangle partition satisfies the same clues. Published Shikaku puzzles normally aim for one unique solution so each step can be justified by logic rather than guessing.