Cut the grid into rectangles so each holds exactly one number, and that number is the rectangle's area
Shikaku is a logic puzzle about dividing a grid into boxes. Numbers are scattered over the squares, and you cut the whole grid into rectangles so that every rectangle holds exactly one number and that number equals the rectangle's area. A 6 has to become a 1×6 or a 2×3 box, a 7 can only be a straight line of seven, and a 1 is a single square. There is no arithmetic beyond that and no guessing: the numbers, the edges of the grid and the boxes you have already drawn are enough to place every box. Ours builds a new grid every time you press New, and a solver checks it has exactly one answer before you see it.
Pick a level: easy is a 6×6 grid with boxes of up to 8 squares, medium is 8×8 with boxes up to 10, hard is 10×10 with boxes up to 12.
Press New puzzle. Each number sits inside the box it belongs to; the number tells you how many squares that box covers.
Drag from one corner of a box to the opposite corner to draw it. Or tap one corner, then tap the opposite corner. Tap the same square twice for a box of one square.
Tap a box you have drawn to erase it. Drawing over existing boxes replaces them.
On a keyboard, move with the arrow keys, press Space on one corner and again on the opposite corner, Backspace to erase the box under the cursor, Escape to cancel a corner and Ctrl+Z to undo.
With Show clashes on, a box that holds no number, two numbers, or a number that does not match its area turns red.
Cover the whole grid with correct boxes and the puzzle ends, with your time saved as a best for that level.
Spatial reasoning and factor sense. Each number limits its box to a few shapes, the factor pairs of the number, and to the positions where that shape fits without swallowing another number. Solving means checking those options against the edges of the grid and against each other, keeping the ones that remain possible in mind, and committing only when a square can belong to just one box. It exercises visual estimation of lengths and areas, quick multiplication facts and the planning habit of working from the most constrained part of the board outward. Another logic game to try next: Hashi (Bridges).
Start with numbers that have only one possible shape and position, often big numbers near a wall or a corner, and numbers whose neighbours box them in.
Prime numbers like 5, 7 and 11 can only be straight lines. If the line does not fit across, it must go down.
Look at squares, not only numbers: an empty square in a corner can usually be reached by just one or two numbers, which tells you which box must cover it.
A box can never contain a second number, so a number sitting between two others limits how far its neighbours' boxes can stretch.
The numbers always add up to the number of squares in the grid, so every square is used exactly once and nothing is left over.
Draw the boxes you are sure of first and leave the uncertain ones; every box drawn removes options from the rest.
Shikaku is a logic puzzle on a grid with numbers on some squares. You divide the grid into rectangles so that each rectangle contains exactly one number, and that number is equal to the rectangle's area, the count of squares it covers.
Shikaku is Japanese for square or four corners. The puzzle is also known in English as Divide by Box or Rectangles.
Yes. A square is a rectangle, so a 4 can be a 2×2 box as well as a 1×4 line, and a 1 is a single square on its own.
Yes. The generator cuts the grid into random boxes and puts each box's area on one of its squares. A solver then tries every box each number could make; if it finds a second way to cover the grid, the number of a box that differs is moved to another square of that box and the check runs again. A puzzle is shown only when exactly one answer is left.
Drag your finger from one corner of the box to the opposite corner, or tap one corner and then the other. Tap a box to erase it, or use Undo.
Grid size and the largest box: easy is 6×6 with boxes of up to 8 squares, medium is 8×8 with up to 10, hard is 10×10 with up to 12. Each level keeps its own best time.
It is free with no sign-up. Your best time per level, the number of puzzles you have solved and the Show clashes setting are saved in this browser only.