How do you play Shikaku?

Divide the grid into rectangles along its lines. Each rectangle must hold exactly one number, and that number must equal its area, so a 6 sits in a 2 x 3 or 3 x 2 rectangle, or a 1 x 6 strip where the grid allows it. Every square belongs to exactly one rectangle: no gaps and no overlaps. A rectangle over a 2 and a 4 is not allowed even though its area of 6 equals their sum, because it holds two numbers. The board here counts as solved only when every rectangle you placed follows both rules and every square is covered once.

Does every Shikaku puzzle here have exactly one solution?

Yes. Each puzzle starts as a split of the grid into rectangles drawn from its seed, and one square of each rectangle gets that rectangle's area as its number. A solver then lists every rectangle each number could fill and narrows those lists by logic until nothing changes. The puzzle is offered only when that narrowing settles every rectangle on its own, which means there is exactly one solution and nobody has to guess to reach it. A split whose numbers allow a second solution, or that narrowing alone cannot settle within the solver's step limit, is dropped and the next split from the same seed is tried, up to 80. If none pass, the page says so and names the next seed to try.

What does the Hint button do?

It checks your board in order. First it names a rectangle that breaks a rule and says which rule. Next it points to squares covered by more than one rectangle. Then it names a rectangle that follows the rules on its own but is not part of the only solution. When everything on the board is right, it names a number that has only one rectangle left that fits the open squares, or a square that only one number can still reach. If neither exists, it shows one rectangle of the solution. It outlines the rectangle or squares on the grid and never places anything for you, and each hint adds one to the hint count beside your progress.

Can I print a Shikaku puzzle?

Yes. Print sends a sheet with the numbered grid, headed with its size and seed, and the rules underneath. Tick the box to add the answer on a second page, where heavy lines mark the edges of each rectangle. Squares print at 20 mm on grids up to 7 x 7 and shrink to 15 mm on a 10 x 10, so every grid fits within 150 mm. Copy puts the same grid on the clipboard as text, with each of your rectangles shown as a letter.

What is the seed, and can I play the same puzzle again?

The seed is a whole number from 1 to 999999. The generator draws its random numbers from a fixed formula seeded by the grid size and the seed, so the same pair gives the same puzzle on any device. The size and seed of the puzzle on the board are shown above it and in the Seed box. To open a puzzle again, choose its size, type its seed and press Play seed. New puzzle picks a random seed at the chosen size.

Is my progress saved?

Yes, in this browser only. The puzzle on the board, your rectangles and its hint count are kept, along with up to 9 earlier puzzles you left with a rectangle on the board or a hint used, so a reload or a later visit opens where you left off. Resume reopens an unfinished puzzle with its rectangles, and Play again reopens a solved one on an empty grid. Undo reaches back through up to 400 moves made since the puzzle was opened in this visit. Nothing is uploaded, and the Start over button at the top of the page forgets all of it. If the browser refuses storage, the header above the progress says the puzzle is not being saved, and it still plays.

Shikaku

Split a numbered grid into rectangles so that each one holds exactly one number equal to its area. Every puzzle here is generated on this page from its own split of the grid, from 5 x 5 to 10 x 10, and offered only after a solver has found exactly one solution and reached it without guessing. Drag from one corner to the opposite corner, tap one corner and then the other, or use the arrow keys and Space; a row of buttons under the grid makes the same moves at phone size. A rectangle turns red the moment it breaks a rule, a square covered twice turns red too, and the status line under the progress says why. Hint points to a rectangle that has to go, or to the next rectangle or square you can work out. Your progress and recent puzzles stay in this browser, the same size and seed make the same puzzle on any device, and any puzzle prints, with its answer on a second page if you want it.

puzzleno puzzle yet

Setting up the board

Your saved puzzle, or a new one, appears here in a moment.

progresssaved once you play

placed: none yet
covered: none yet
selecting: no corner marked
clues left: none yet
hints: none yet
keys: arrows move, Space marks a corner, Delete removes

ruleone number in each rectangle, equal to its area; every cell covered once

Setting up the board.

Grid

Seed

Rectangles

none yet

Covered

none yet

Solutions

none yet

Print the answer on a second page

Drag from one corner of a rectangle to the opposite corner, or tap one corner and then the other. With no corner marked, a tap on a rectangle removes it. On a keyboard, the arrow keys move, Space marks the first corner and Space again at the opposite corner places the rectangle, Escape clears a marked corner, Delete removes the rectangle under the cursor, and Ctrl+Z or Cmd+Z undoes. The buttons under the grid do the same moves at a size that suits a phone. A rectangle turns red when it breaks a rule, and a square covered twice turns red too. Hint names a broken rectangle or an overlap first, then a rectangle that is not part of the only solution, then the next rectangle or square you can work out. The size and seed on the board make the same puzzle again anywhere, and your progress stays in this browser.

Your recent puzzles

No earlier puzzles yet. Each puzzle you leave with a rectangle on the board or a hint used is kept here with its seed and your rectangles, up to 9, so you can go back to it.

How the rules are checked

A 2 x 3 rectanglearound exactly one clue
valid only if that clue is 6, its area
Two rectangles overlap, one cell uncoveredevery clue used
not complete: 1 cell covered twice and 1 cell not covered, both marked
A 2 x 3 rectangle over clues 2 and 4area 6 = 2 + 4
invalid: a rectangle holds exactly one clue

Accuracy. Every puzzle is generated here from an original split of the grid into rectangles, never copied from a puzzle book, and is offered only after a solver confirms its numbers have exactly one solution, reachable without guessing. A board counts as complete only when each rectangle holds exactly one number equal to its area and every cell is covered exactly once. There is no difficulty rating, because none is measured.

Common questions

How do you play Shikaku?: Divide the grid into rectangles along its lines. Each rectangle must hold exactly one number, and that number must equal its area, so a 6 sits in a 2 x 3 or 3 x 2 rectangle, or a 1 x 6 strip where the grid allows it. Every square belongs to exactly one rectangle: no gaps and no overlaps. A rectangle over a 2 and a 4 is not allowed even though its area of 6 equals their sum, because it holds two numbers. The board here counts as solved only when every rectangle you placed follows both rules and every square is covered once.
Does every Shikaku puzzle here have exactly one solution?: Yes. Each puzzle starts as a split of the grid into rectangles drawn from its seed, and one square of each rectangle gets that rectangle's area as its number. A solver then lists every rectangle each number could fill and narrows those lists by logic until nothing changes. The puzzle is offered only when that narrowing settles every rectangle on its own, which means there is exactly one solution and nobody has to guess to reach it. A split whose numbers allow a second solution, or that narrowing alone cannot settle within the solver's step limit, is dropped and the next split from the same seed is tried, up to 80. If none pass, the page says so and names the next seed to try.
How do I draw a rectangle on a phone or with a keyboard?: With a finger or a mouse, drag from one corner square to the opposite corner, or tap one corner and then the other. With no corner marked, tapping a rectangle that is already on the board removes it. On a keyboard, the arrow keys move around the grid, Space marks the first corner, and Space again at the opposite corner places the rectangle; Escape clears a marked corner, Delete or Backspace removes the rectangle under the cursor, and Ctrl+Z or Cmd+Z undoes. On large grids the squares can be smaller than a fingertip on a phone, so the row of buttons under the grid moves the cursor, marks corners and removes rectangles at a size that is easy to tap.
What does the Hint button do?: It checks your board in order. First it names a rectangle that breaks a rule and says which rule. Next it points to squares covered by more than one rectangle. Then it names a rectangle that follows the rules on its own but is not part of the only solution. When everything on the board is right, it names a number that has only one rectangle left that fits the open squares, or a square that only one number can still reach. If neither exists, it shows one rectangle of the solution. It outlines the rectangle or squares on the grid and never places anything for you, and each hint adds one to the hint count beside your progress.
Can I print a Shikaku puzzle?: Yes. Print sends a sheet with the numbered grid, headed with its size and seed, and the rules underneath. Tick the box to add the answer on a second page, where heavy lines mark the edges of each rectangle. Squares print at 20 mm on grids up to 7 x 7 and shrink to 15 mm on a 10 x 10, so every grid fits within 150 mm. Copy puts the same grid on the clipboard as text, with each of your rectangles shown as a letter.
What is the seed, and can I play the same puzzle again?: The seed is a whole number from 1 to 999999. The generator draws its random numbers from a fixed formula seeded by the grid size and the seed, so the same pair gives the same puzzle on any device. The size and seed of the puzzle on the board are shown above it and in the Seed box. To open a puzzle again, choose its size, type its seed and press Play seed. New puzzle picks a random seed at the chosen size.
Is my progress saved?: Yes, in this browser only. The puzzle on the board, your rectangles and its hint count are kept, along with up to 9 earlier puzzles you left with a rectangle on the board or a hint used, so a reload or a later visit opens where you left off. Resume reopens an unfinished puzzle with its rectangles, and Play again reopens a solved one on an empty grid. Undo reaches back through up to 400 moves made since the puzzle was opened in this visit. Nothing is uploaded, and the Start over button at the top of the page forgets all of it. If the browser refuses storage, the header above the progress says the puzzle is not being saved, and it still plays.

Every puzzle is generated here from an original split of the grid into rectangles, never copied from a puzzle book, and is offered only after a solver confirms its numbers have exactly one solution, reachable without guessing. A board counts as complete only when each rectangle holds exactly one number equal to its area and every cell is covered exactly once. There is no difficulty rating, because none is measured.