Sudoku asks you to place the digits 1–9 so no row, column or box repeats; Shikaku asks you to divide a grid into rectangles whose areas match the given numbers. Both have a unique solution reached by logic alone, but Sudoku is about elimination of symbols while Shikaku is about shapes and area.
Side by side
| Shikaku | Sudoku | |
|---|---|---|
| Goal | Divide the grid into rectangles | Fill every cell with a digit |
| Clues | Numbers = rectangle areas | Pre-filled digits |
| Maths | Multiplication and factors | None — digits are just symbols |
| Main skill | Spatial reasoning | Pattern elimination |
| Typical size | 5×5 to 25×25 | 9×9 |
| Published by Nikoli | Since 1989 | Named and popularised from the 1980s |
| Unique solution | Yes (well-made puzzles) | Yes (well-made puzzles) |
In detail
Similarities. Both puzzles are pure logic: no luck, no general knowledge, and a single correct answer. Both reward scanning for forced moves first, and both have advanced techniques built on “if this, then that” reasoning.
Differences. Sudoku’s difficulty comes from long elimination chains across rows, columns and boxes. Shikaku’s comes from geometry: how rectangles block each other, which cells only one number can reach, and how areas add up. Shikaku also scales freely — a 25×25 board is common — while classic Sudoku is fixed at 9×9.
History. Sudoku’s modern form appeared in the US in 1979 as “Number Place” and took its now-famous name from Nikoli in Japan, from where it spread worldwide in the 2000s. Shikaku was first published by Nikoli in 1989. See our history of Shikaku.
Which should you play?
If you love Sudoku and want something fresh that uses the same careful logic in a visual way, Shikaku is an excellent next puzzle. Its rules are even simpler, small grids are quicker, and big grids can be just as deep.
Play Shikaku now
Six sizes, three levels, every puzzle with a unique solution.
Questions
Is Shikaku harder than Sudoku?
Neither is harder in general — both range from very easy to very hard. Small Shikaku grids are often quicker than a typical Sudoku.
Do Shikaku and Sudoku use the same techniques?
They share the logic-only approach and the idea of forced moves, but the specific techniques differ because Shikaku is about shapes rather than digits.