What is Shikaku?
Shikaku is a Japanese logic puzzle about rectangles. You get a grid scattered with numbers, and you split the whole grid into rectangles so that every rectangle holds exactly one number - and that number is its size. It takes seconds to learn and can take a lot longer to master.
You might also know it as Rectangles, Divide by Box, Divide by Squares or Shikaku ni Kire - "divide into squares" in Japanese. It was made popular by Nikoli, the Japanese puzzle publisher also behind the name Sudoku. Plotwork is a Shikaku game: the same rules, with daily puzzles, speedruns, races against friends and worldwide tables.
The rules
- Fill the grid with rectangles. Every square is used, and no two rectangles overlap.
- Each rectangle holds exactly one number. Not none, not two.
- The number is the rectangle's area - how many squares it covers. A 6 could be 1 × 6, 2 × 3, 3 × 2 or 6 × 1.
- Squares count too. A 4 can be a 2 × 2 square as well as a line of four.
That's all. A good Shikaku puzzle has exactly one answer, and you never need to guess: every rectangle can be worked out from the ones around it.
How to solve Shikaku: tips that work
1. Start with the numbers that have only one choice
Look for numbers squeezed into a corner or a narrow gap. A 3 against a wall with a number on each side can often only go one way. Place those first - each one you fix takes choices away from its neighbours.
2. Big numbers first, especially near the edges
A 12 or a 16 needs a lot of room. There are usually only a couple of places it fits without swallowing another number, and the edge of the board rules out half of them.
3. Prime numbers make lines
A 2, 3, 5, 7, 11 or 13 can't be a rectangle more than one square wide - it has to be a straight line. That makes primes quick to pin down.
4. Find the squares only one number can reach
Pick an empty square and ask which numbers could possibly stretch to cover it. If only one can, that square belongs to that number's rectangle - which often tells you its shape.
5. Count what's left
The numbers always add up to the number of squares on the board. When a region is nearly closed off, add up the numbers inside it: if they already match the space, nothing from outside can come in.
6. In Plotwork: the "?"
Some Plotwork puzzles hide a number behind a ?. It still has one real size - you just have to work it out from the space the other rectangles leave. Treat it like the last piece of a jigsaw.
Why Shikaku is good for you
Like Sudoku, Shikaku is pure logic - no maths beyond multiplying small numbers, no language, no luck. It trains the same things: spotting patterns, holding several possibilities in your head, and ruling them out one by one. It's also quick. A small Shikaku takes under a minute; a big one makes a good coffee break.
Play Shikaku every day with Plotwork
Plotwork turns Shikaku into a game you'll want to come back to:
- A daily puzzle - one big board, the same for everyone, every day. Play it free in your browser.
- Speedruns - boards get bigger as the clock gets tighter.
- Zen mode - no clock, 32 boards from tiny to giant, some in unusual shapes.
- Races - the same board, at the same moment, against friends or strangers.
- Leagues and seasons - worldwide tables that start again every 3 hours, every day and every week.