Is Shikaku Like Sudoku? Why It's a Rectangle Puzzle, Not a Number Puzzle
Shikaku guide · 6 min read
It is a natural assumption. Shikaku has a grid, it has numbers, it is a Japanese logic puzzle from the same publisher as Sudoku, so surely it plays like Sudoku? The answer is a clear and slightly surprising no. Despite the numbered grid, Shikaku is barely related to Sudoku in how you actually solve it. In Sudoku you fill cells with digits; in Shikaku you never write a number at all, you draw rectangles. Understanding that difference is the key to "getting" Shikaku, and it is why the puzzle feels so refreshing to Sudoku fans looking for something new. Here is how Shikaku and Sudoku really compare. Want to feel the difference? Play a Shikaku puzzle and see.
The short answer
No, Shikaku is not a type of Sudoku. They are both grid-based logic puzzles popularised by Nikoli, and both have a single solution reached by pure deduction, so they share a certain spirit. But the actual mechanic could hardly be more different. The defining difference: in Sudoku the numbers are the answer you produce, while in Shikaku the numbers are fixed clues you are given, and your job is to draw rectangles around them.
What you actually do is completely different
This is the heart of it.
In Sudoku, you start with a grid that is mostly empty, and you write digits into cells so that every row, column, and 3×3 box contains the numbers 1 to 9 exactly once. The whole activity is placing numbers. The finished puzzle is full of the digits you added.
In Shikaku, the numbers are already printed and never change. You do not add a single digit. Instead, you divide the grid into rectangles by drawing boundary lines, so that each rectangle surrounds exactly one of those numbers, and the number equals the rectangle's area. The finished puzzle is the same set of numbers, now wrapped in the rectangles you drew. You are not filling, you are partitioning.
That single reversal, placing numbers versus drawing regions, makes the two puzzles feel worlds apart even though they look like cousins on the shelf.
No rows, columns, or boxes
Sudoku is built entirely on its three constraints: each digit once per row, once per column, once per 3×3 box. That "no repeats per line" rule is the soul of Sudoku.
Shikaku has none of it. There is no rule about rows, columns, or boxes at all. A "3" can appear several times across a row, and that is perfectly fine. Shikaku's only real rules are that the rectangles tile the whole grid without overlapping, and that each rectangle's area matches its single number. It is a tiling puzzle, not a number-placement puzzle, and the absence of Sudoku's line rules is one of the clearest signs they are different games.
Side by side
| Sudoku | Shikaku | |
|---|---|---|
| What you do | Write digits into cells | Draw rectangles around given numbers |
| The numbers are | The answer you produce | Fixed clues (each equals a rectangle's area) |
| Core rule | Each digit once per row, column, box | Divide the grid into rectangles, area = number |
| Row/column rule? | Yes | None |
| The maths | None (digits are just symbols) | Factoring and area (every clue is a factor pair) |
| Feel | Number placement | Grid division / tiling |
There is even a mathematical difference. In Sudoku the digits are really just nine symbols; you could play with colours instead. In Shikaku the numbers genuinely mean something, because each one is an area you have to factor into a width and a height. That makes Shikaku quietly a maths puzzle in a way Sudoku is not, as we explore in Shikaku for math.
So why do people compare them?
The comparison is natural for three reasons: both are grid puzzles with numbers, both come from Nikoli, and both are solved by pure logic with a guaranteed single solution. If you enjoy the deductive, no-guessing satisfaction of Sudoku, you will almost certainly enjoy Shikaku, which is exactly why Sudoku fans are often pointed toward it.
But "appeals to the same people" is not the same as "plays the same way." Once you have drawn a few rectangles, the difference is obvious: you stop thinking about which digit goes in a cell and start thinking about which shape fits a number. It is the same logical pleasure, reached by an entirely different route.
The verdict
Shikaku is a number-grid logic puzzle, a cousin of Sudoku in the family tree, but it is not a Sudoku or a Sudoku variant. It swaps number-placement for grid-division, drops the row-and-column rules entirely, and adds a genuine factoring element. If Sudoku has started to feel repetitive, that difference is precisely why Shikaku feels like a breath of fresh air: familiar enough to pick up instantly, different enough to surprise you.
The best way to appreciate it is to draw a few rectangles yourself. Play a Shikaku puzzle now, or learn the rules and feel how different it is from filling in a Sudoku.
Frequently asked questions
Is Shikaku like Sudoku?
Not really. Both are grid-based logic puzzles from Nikoli with a single solution, so they share a spirit, but they play completely differently. In Sudoku you write digits into cells under row, column, and box rules. In Shikaku you draw rectangles around fixed numbers so each rectangle's area equals its number. You place numbers in Sudoku; you divide the grid in Shikaku.
Is Shikaku a type of Sudoku?
No. Shikaku is not a Sudoku or a Sudoku variant. It has no row, column, or box rules, and you never place numbers, you partition the grid into rectangles. It only resembles Sudoku in that both are numbered grid puzzles solved by logic.
What is the difference between Shikaku and Sudoku?
In Sudoku you fill empty cells with digits 1 to 9 so each appears once per row, column, and 3×3 box. In Shikaku the numbers are given clues, and you divide the grid into non-overlapping rectangles so each rectangle contains one number equal to its area. Sudoku is number placement; Shikaku is grid division, with a built-in factoring element.
Should I play Shikaku if I like Sudoku?
Yes. Although the mechanic is different, Shikaku offers the same deductive, no-guessing satisfaction that Sudoku fans enjoy, with a fresh twist: you draw rectangles and factor numbers instead of placing digits. It is a natural next puzzle for anyone who wants Sudoku's logic in a new form.