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Sudoku FAQ

What is sudoku?

Sudoku is a logic puzzle, standardly consisting of a nine by nine (9x9) grid of individual square cells. Each row, column, and three by three of the grid contains the numbers one to nine once. A true sudoku grid has one unique solution, and can be solved without guesswork. Sudoku puzzles may be any size, however, and for instance 6 x 6 are not uncommon particularly with some sudoku variants. In addition they can get really big, for instance 25 x 25 is occasionally seen in publication. Apparently someone has even created a 100 x 100 sudoku, which with it's 10,000 individual cells would be a daunting challenge for a human solver!

What does sudoku mean?

The name Sudoku is apparently an abbreviation for Suji wa dokushinsha ni kagiru. Clear? Well, we're told that means "numeral(s) limited to a single person". This probably refers to the fact that only one of each digit can appear in a row, column or box.

Sudoku or su doku?

There doesn't seem to be a definitive 'correct' name, however virtually everywhere seems to use 'sudoku', hence we have here at Saidwhat too. The exception is The Times newspaper in the UK, which uses 'su doku'. It is also called 'number place' in some publications.

How do you play sudoku?

You are provided with an incomplete grid, and must deduce what number from 1 - 9 goes where in each row, column and 3 x 3 box (in the standard 9 x 9 puzzle) until you have completed the puzzle to form a valid sudoku grid. In 6 x 6 sudoku you have 3 x 2 boxes, and so on.

What makes one puzzle more difficult or easier than another?

In general, puzzles where you are given less starting numbers are harder than those where there are several, as you need to put more effort in to get started and there is often only one avenue you can pursue at a time (one possible number to find). Also, with easier puzzles you can work out a number straightforwardly as there is only one candidate, whilst with harder puzzles you may have to perform more complex logic - for a fuller explanation, look at the Strategy Page.

Where can I play sudoku?

You can play thousands of sudoku puzzles with our online sudoku player.

How many variants of sudoku are there and what are they?

It is very hard to give a definitive list of types of sudoku puzzles, as new types are always being invented and many come under several names. Here I give a list of the types of sudoku puzzle I know about in alphabetical order; if you know of any others please send them to me. The majority of these puzzles are followed by a link to a (free) sample of that sudoku variant puzzle that you can play on our puzzle website, or elsewhere, online right now.

16 x 16 SUDOKU

This is sudoku but on a larger grid than usual. The 16 x 16 grid contains 256 cells, compared to the 81 of normal sudoku. The boxes are now 4x4 in size, containing 16 cells, rather than 3x3. The puzzles may use numbers of quite often a combination of numbers and letters. These puzzles take a lot longer to solve than 9x9 sudoku. You can play them in 16x16 Sudoku Magazine.

25 x 25 SUDOKU This is the biggest variant of sudoku that is standardly seen in publication. The puzzle is massive, with a total of 625 cells per puzzle! The aim is to place the numbers from 1 - 25, or a combination of 25 letters and numbers, in each row, column and this time each 5x5 box. With 25 different values in each of the 75 regions in this puzzle to keep track of, then this puzzle can take several days for someone to solve. For those up for the challenge there is 25 x25 Sudoku Magazine to tackle.


Arrow sudoku is a rare sudoku variant that is infrequently published. The grid contains 1 - 9 once in each row, column and box as per normal sudoku, but the grid also contains arrows that have a circle at the end of the tail. The cells along the body of the arrow sum to the circled cell. Thus if the body of the arrow passes through two cells then the circled cell contains the sum of those two cells. It is easier to describe this puzzle by showing what the grid looks like, here is an example of a Arrow Sudoku grid, note how distinctive it is compared to many other sudoku puzzle types. Notice how in that example you can instantly place the '9' in the bottom row in a couple of seconds without any thought other than observing the pattern of the arrows. Can you see how?


Calcudoku is a variation on killer sudoku which is itself a sudoku variation. Just like in killer sudoku the grid is divided into lots of small regions, but whereas in killer these are always sum regions, in calcudoku they may require subtraction, division or multiplication instead. They are also usually marked with thick lines rather than dotted cages, there are no 'box' regions and finally repetition is allowed within these regions as long as it does not break the rule that a number may only appear once in each row / column. Because subtraction and division are non-commutative operations, it is prescribed that all numbers in a region are subtracted from the largest number in that region, or the largest number is divided by the other numbers in the region for a division region. Some puzzles printed in popular newspapers only allow these regions to only contain two cells, for which there does not appear to be a logical reason. You can play Calcudoku online at the Puzzle Club and if you prefer to print and play, look at Calcudoku Magazine.


This variant is different more in display than functional terms, displaying as it does the puzzle in a circle format. There are many types and variations available, with differing number of regions and constraints. Many drop the box constraint and simply have spokes and circles to represent the row and column regions. Other constraints are sometimes applied, you may have played variants of this puzzle with eight or nine cells per region, for instance spider sudoku often has nine and re-introduces the box constraint.
Circle Sudoku >>>


This is in a sense the opposite of the non-consecutive sudoku: certain cells are marked as being consecutive, traditionally with a slim white bar between the consecutive adjacent cells. This tells the solver that those numbers are consecutive; thus if a cell contains '7' then the consecutively marked adjacent cell contains only 6 or 8. Thus consecutive cells convey a lot of information. This property means that these puzzles can be created with very few givens. If you like this puzzle, take a look at Consecutive Sudoku Magazine.


A name for any type of sudoku puzzle that adds extra regions on the standard row, column and box constraints. Thus sudoku X, slash sudoku and offset sudoku are all types of extra regions sudoku. Another common extra regions sudoku puzzle adds four more 9 x 9 boxes into the mix.
Extra Regions Sudoku >>>

We can also create custom sudoku puzzles, for instance for your company marketing or advertising campaign, containing your company initials as extra regions in the sudoku puzzle. Here is an example using 'P' and 'C' as extra regions for Puzzle Club.
Marketing Sudoku >>>


This sudoku variant is hutosiki but with the box constraint added back in. Inequalities are used to determine the relations between different cells. There are also variants where the inequalities are placed between cells that are diagonally next to each other, not just horizontally or vertically.


Greek Latin sudoku is an extension of the usual sudoku puzzle in that, in addition to having numbers occurring once in each region, there is also a letter that occurs once per region. Thus in a small grid such as 4 x 4 each row and column contains 1 - 4 and A - D exactly once. In addition, each combination of letter and number (A1 through to D4 in the 4x4 puzzle) appears once. Here is an example Greek Latin Sudoku under the name of ABC Doku.


This is very close to sudoku, but is not considered by everyone as a sudoku variant but rather a separate puzzle as it does drop the box constraint and adds a new method. Hutosiki, also called futoshiki, is usually on a 5 x 5, 6 x 6 or 7 x 7 grid, and adds inequality signs to the puzzle. Certain cells are marked as greater or less than one or more of their neighbours, and you must use these constraints to help solve the puzzle. If you like futoshiki, take a look at Futoshiki Magazine.
5x5 Futoshiki Puzzle
7x7 futoshiki puzzle


This is a variant that is usually played on a grid compared of hexagonal cells to create a visually interesting puzzle. The gimmick with isosudoku is the introduction of partial regions running along the diagonals from left to right across the grid, all of which contain less than the usual nine cells per region apart from the major diagonal running from the first cell to the last cell in the puzzle. The partial logic can introduce some interesting solve rules that may or may not be required to solve the puzzle. You can see a IsoSudoku here. In addition, you can download 50 PDFs of this puzzle in Isosudoku magazine.


Known variously as Jigsaw Sudoku, Irregular Sudoku, and even ZiguZagu in some places! This sudoku variant has the same number of regions as vanilla sudoku, but the box regions are squished. Rather than being the regular 3 x 3 boxes they may take any shape at all, and hence they fit together like jigsaw pieces to form the complete puzzle, hence it is often called jigsaw sudoku. This is a fun variant, and easier played online where you can clearly use colour to demarcate the different regions.
Jigsaw Sudoku Puzzle >>>


Killer Sudoku is a significant variant on vanilla sudoku. It has no givens at all to start you off (apart from some kids killer sudoku to make them easier). The row, column and box constraints remain, but the grid is divided into individual regions. You are told what those regions sum up to, and must use that to deduce where each number goes. As such addition is required, and the puzzle is often considered a cross between sudoku and kakuro. You may also need killer sudoku called add-oku, addoku, or even add doku, depending where you look.
Killer Sudoku puzzle >>>


This is killer sudoku with the X regions from sudoku X added, as such there is even more to consider when trying to solve this puzzle. It is a variant that is not usually seen in mainstream publications such as newspapers and magazines, but it common in sudoku variant magazines.
Killer Sudoku X puzzle >>>


This variant allows the creation of valid sudoku puzzles with very few given cells, due to the significant constraint that adjacent cells cannot contain consecutive values. This is often used for circular sudoku puzzles or puzzles displayed in that manner, particularly when the constraint applies to the edges top, bottom, left and right of the puzzle too.
Non consecutive sudoku | 12 givens sudoku puzzle


There are a couple of varieties of this puzzle. In one variant, you know whether every square is odd or even - this puzzle is fairly rare and very few givens are needed to the implications of this major constraint.

Another version of the puzzle lets you know whether a certain number of cells are all odd or all even, and you must deduce which it is and then solve the puzzle accordingly. The special cells are usually marked in a different colour.
Play odd even sudoku


Offset Sudoku is a special type of Extra Regions sudoku. In fact is has an extra 9 regions added to the mix. Not only does each row, column and box have to contain 1 - 9 uniquely, but the order within each box must too. In other words, the first cell in each box must be 1 - 9, and so on for the second, third, fourth... ninth 9 x 9 box.
Offset Sudoku Puzzle >>>


Samurai sudoku involves the merger of two or more sudoku grids. A common version has five sudokus overlapping in the shape of an X. A good samurai will require you to use the numbers in the overlapping regions to help solve the puzzle, though they can be formed by merging puzzles created in isolation that have a region in common (for instance boxes 1 / 9 or 3 / 7). Some compilers consider this method to be cheating! Furthermore, samurai sudoku are sometimes mixed, so for instance one puzzle within the overall grid will be a jigsaw sudoku, another a sudoku X and so on.
Samurai Sudoku >>> | Buy Samurai Sudoku or alternatively you can download Samurai Sudoku Magazine containing 50 puzzles.


This is a type of samurai sudoku that has a much more tightly overlapping set of grids than orthodox samurai puzzles. Rather than having one region overlap, these puzzles share a large number of regions between them. Thus one of the grids is fully embedded in the regions of the other four puzzles, given the grid its shape. This is also known in some places as flower sudoku.
Samurai Star Sudoku >>>


Slash Sudoku is literally half way between Sudoku and Sudoku X, as it contains one extra region - one of the main diagonals. Therefore it is a hybrid of these two puzzles. I've not seen it published anywhere else other than here. The reason I made it is simple - when I first wrote my Sudoku X creator it was quite slow, so I saved the puzzles that were half-way to being valid (e.g. had one unique diagonal!).
Slash Sudoku puzzle >>>


Sudoku + is a variant puzzle that has numbers around the outside of the grid, at the start/end of each (or at least many) rows and columns. These numbers indicate the sum total of the three cells nearest to the number in that row/column. As such it can be seen as a partial killer sudoku puzzle. Here is an example of a Sudoku + puzzle. Other variations of this are sometimes seen with for instance subtraction or multiplication required instead of addition: these are "Sudoku -" and "Sudoku X" respectively.


The most common sudoku variant, and a special case of extra regions sudoku. Here there are two extra regions, the main diagonals, which give the puzzle the distinctive X-shape. Because of these two extra regions, you need state less givens in order to still create a puzzle with one valid solution that can be reached without guesswork.
Sudoku X puzzle >>> or alternatively Sudoku X Magazine.


The skyscraper sudoku is an interesting variant of sudoku and is a hybrid with the skyscraper puzzle. In this game, you must work out where to place 1 - 9 under normal sudoku rules, with the addition of the fact that at the start and end of each row and column is a number, which states how many blocks can be seen in that direction. This is based on the numerical value of the numbers, thus nothing can be seen over a 9 and everything can be seen over a 1. There are many interesting rules and deductions that can be made on the basis of the sky scraper regions.


Toroidal Sudoku is one of the least common sudoku variants. It is like an even more extreme version of jigsaw sudoku. In toroidal sudoku, the regions can wrap around the top, bottom, left and right of the puzzle, just like your Pacman character going off the edge of the screen and coming back on the other side!

This puzzle is much easier played online where colour is used to show the regions; with thick black and white borders on paper half the battle is working out which cell belongs to each region!
Toroidal Sudoku Puzzle >>>
Toroidal Sudoku X Puzzle


This is not a true variant, in that the puzzle is functionally equivalent to standard sudoku. However the numbers are substituted with letters, usually A - I. There are other various like quiz sudoku, QuizDoku and so on, where certain cells are shaded and must form a word. Some of these puzzles require you to work out the word to get to a valid solution for the puzzle.


As the name suggests, this is sudoku but on a grid that mimics three dimension. There can be a range of shapes, such as cubes, with regions 'going around corners', as it were, depending on the shape of the regions and the shape of the 3D object being simulated on paper.

Play Thousands of Puzzles in our Puzzle Club >>> or if you wish to publish, then you can also Buy puzzles

First published: May 2005. Last update: February 2010