Sudoku has evolved far beyond the classic 9x9 grid. Today there are dozens of recognized variants, each adding unique constraints that change how you think about number placement. This guide compares the 8 most popular types of Sudoku, from the familiar Classic puzzle to the massive Mega 16x16, so you can find the variant that matches your skill level and interests.
Comparison Table
The table below provides a quick reference for every variant. Use it to compare grid sizes, core rules, difficulty levels, and ideal player profiles at a glance.
| Variant | Grid Size | Key Rule | Difficulty | Best For |
|---|---|---|---|---|
| Classic 9x9 | 9 x 9 | Each row, column, and 3x3 box contains 1-9 | Easy - Hard | Everyone; the standard starting point |
| Killer Sudoku | 9 x 9 | Cages with target sums; no repeats within a cage | Medium - Expert | Players who enjoy arithmetic challenges |
| Sandwich Sudoku | 9 x 9 | Clues show the sum of digits between the 1 and 9 in each row/column | Medium - Hard | Logical thinkers who like deduction puzzles |
| Mini Sandwich | 6 x 6 | Sandwich clues on a smaller grid using digits 1-6 | Easy - Medium | Beginners exploring sandwich-style logic |
| Diagonal Sudoku | 9 x 9 | Both main diagonals must also contain 1-9 | Medium | Classic players seeking one extra constraint |
| Little Killer | 9 x 9 | Clues outside the grid show the sum along a diagonal | Hard - Expert | Advanced solvers who like sum-based logic |
| Mini 6x6 | 6 x 6 | Each row, column, and 2x3 box contains 1-6 | Easy | Beginners, kids, and quick sessions |
| Mega 16x16 | 16 x 16 | Each row, column, and 4x4 box contains 1-16 | Expert | Experienced players wanting a marathon puzzle |
Classic 9x9 Sudoku
Classic Sudoku is the foundation of every other variant on this list. The rules are straightforward: fill a 9x9 grid so that every row, every column, and every 3x3 box contains the digits 1 through 9 exactly once. No arithmetic, no extra constraints — just pure logical deduction.
Because of its simplicity, Classic Sudoku scales well across difficulty levels. Easy puzzles provide plenty of given digits for quick solves, while Hard puzzles may require advanced techniques like X-Wings and Swordfish. It is the best place to build the foundational skills you will need for every other variant.
If you are new to Sudoku, start here. Read our complete beginner's guide for rules, strategies, and tips.
Killer Sudoku
Killer Sudoku replaces the pre-filled numbers of Classic Sudoku with dotted-line "cages." Each cage has a target sum, and the digits inside it must add up to that sum without repeating. You still follow the standard row, column, and box constraints, but now you also need arithmetic skills to narrow down candidates.
The key technique in Killer Sudoku is the "Rule of 45," which states that every row, column, and box sums to 45. By subtracting known cage values, you can deduce what remains. Killer puzzles are rated Medium to Expert and are a natural next step for players who have mastered Classic Sudoku.
Learn the full ruleset in our Killer Sudoku rules guide.
Sandwich Sudoku
Sandwich Sudoku uses a standard 9x9 grid with no pre-filled numbers (or very few). Instead, clue numbers appear outside the grid indicating the sum of all digits sandwiched between the 1 and the 9 in that row or column. If a row's clue is 35, you know that the cells between the 1 and 9 in that row must add up to 35.
Solving a Sandwich puzzle requires working out where the 1 and 9 can go first, then using the sandwich sum to constrain the remaining digits. This variant demands a different type of logical reasoning compared to Classic Sudoku, making it feel fresh even for experienced players.
See our Sandwich Sudoku rules guide for detailed strategies.
Mini Sandwich
Mini Sandwich applies the same sandwich-sum concept to a compact 6x6 grid using digits 1 through 6. The "bread" digits are 1 and 6 instead of 1 and 9, and the 2x3 box regions keep the grid manageable.
This variant is an excellent stepping stone. It lets you practice sandwich logic without the complexity of a full 9x9 grid. Puzzles typically take 5 to 10 minutes, making Mini Sandwich ideal for commutes or short breaks.
Diagonal (X) Sudoku
Diagonal Sudoku, sometimes called X-Sudoku, adds one rule to Classic Sudoku: the two main diagonals (from corner to corner) must each contain the digits 1 through 9 without repeats. This single constraint has a surprisingly large impact on solving strategies because the diagonals intersect every box on the grid.
Because each diagonal provides 9 additional unique-digit constraints, Diagonal puzzles often feel slightly easier than an equivalently rated Classic puzzle. However, the diagonal rule also opens up unique techniques that reward players who think about the grid in new ways.
Read our Diagonal Sudoku rules guide for a full breakdown.
Little Killer Sudoku
Little Killer Sudoku places small clue numbers along the edges of the grid with arrows pointing diagonally inward. Each clue gives the sum of all the digits along that diagonal line. Unlike Killer Sudoku cages, digits can repeat on a Little Killer diagonal as long as they do not violate the standard row, column, and box rules.
This variant is one of the hardest 9x9 types because the diagonal sums overlap in complex ways. Solvers need to combine sum logic with careful candidate elimination. Little Killer puzzles are best suited for advanced players who enjoy deep analytical challenges.
Our Little Killer Sudoku guide covers the rules and solving techniques.
Mini 6x6 Sudoku
Mini 6x6 Sudoku shrinks the grid to 6 rows and 6 columns divided into 2x3 boxes, using only digits 1 through 6. The rules are identical to Classic Sudoku, just on a smaller scale. Puzzles can be solved in under 5 minutes, even by beginners.
Mini Sudoku is perfect for children learning logic skills, for adults who want a quick mental exercise, or as a warm-up before tackling harder variants. Despite its simplicity, harder-rated Mini puzzles can still provide a satisfying challenge by offering very few given digits.
Mega 16x16 Sudoku
Mega 16x16 Sudoku is the largest standard variant, featuring a 16x16 grid divided into 4x4 boxes. You place the digits 1 through 16 (or sometimes 0-9 plus A-F in hexadecimal notation) so that each row, column, and box contains every value exactly once.
With 256 cells to fill, Mega puzzles require serious time commitment — often 30 minutes to over an hour. The logic is the same as Classic Sudoku, but keeping track of 16 candidates per cell pushes your working memory and concentration to the limit. This is the marathon of the Sudoku world.
Get started with our Mega 16x16 Sudoku guide.
Which Variant Should You Start With?
Choosing the right starting variant depends on your experience level and what kind of challenge you enjoy. Here is a simple decision flow:
- Never played Sudoku before? Start with Mini 6x6. The smaller grid lets you learn the core rules without feeling overwhelmed. Once you can solve Mini puzzles consistently, move up to Classic 9x9.
- Comfortable with Classic Sudoku? Try Diagonal Sudoku next. It adds only one extra constraint, so the learning curve is gentle while still feeling like a fresh challenge.
- Enjoy math and arithmetic? Go straight to Killer Sudoku or Sandwich Sudoku. Both combine number placement with sum-based reasoning. Killer is more structured; Sandwich is more deductive.
- Want the hardest challenge? Take on Little Killer for a tough 9x9 variant, or Mega 16x16 if you want sheer scale.
- Short on time? Mini Sandwich gives you variant-style logic in a compact format you can finish in minutes.
There is no wrong order. Every variant builds on the same foundational logic, so skills transfer between types. The best approach is to play what interests you and move on when you are ready for a new challenge.
Difficulty Ranking
The following ranking orders all 8 variants from easiest to hardest based on the typical solving experience. Keep in mind that individual puzzle difficulty varies — a hard Classic puzzle can be tougher than an easy Killer puzzle.
- Mini 6x6 — Smallest grid, fewest candidates, fastest solves. The easiest entry point into Sudoku.
- Classic 9x9 (Easy) — The standard starting point with plenty of given digits to work from.
- Mini Sandwich — Introduces sandwich sums on a manageable 6x6 grid. Slightly harder than plain Mini because of the arithmetic layer.
- Diagonal Sudoku — Classic rules plus two diagonal constraints. The extra information can actually make certain puzzles easier to crack.
- Classic 9x9 (Hard) — Fewer givens demand advanced techniques like naked pairs, hidden triples, and X-Wings.
- Sandwich Sudoku — Requires strong deduction skills to locate the 1 and 9 before filling in the rest.
- Killer Sudoku — Arithmetic constraints on top of standard Sudoku rules. Demands both logical and numerical fluency.
- Little Killer — Complex overlapping diagonal sums make this one of the hardest 9x9 variants.
- Mega 16x16 — Same logic as Classic, but 256 cells and 16 candidates per cell push endurance and working memory to the limit.