Outside Sudoku
37
61
98
67
39
41
79
31
64
83
75
94
26
18
35
37
52
48
6
5
2
2
8
3
9
4
7
2
8
5
6
7
3
1
5
8
1
8
3
5
7
9
6
2
2
4
8
1
2
5
9
4
7
1
5
9
47
16
85
18
37
62
81
34
26
68
74
31
21
45
97
42
86
31
How to play Outside Sudoku
Standard Sudoku rules apply. Each digit shown outside the grid must appear within the first three cells of that row or column (the nearest 3x3 box). Blue clues on the left/right refer to the first/last three cells of that row; blue clues on the top/bottom refer to the first/last three cells of that column.
Full guide →
Digits outside the grid must appear in the first three cells of that row or column
Easy
Outside Sudoku Easy
Medium
Outside Sudoku Medium
Hard
Outside Sudoku Hard
Expert
Outside Sudoku Expert
What is Outside Sudoku?
Outside Sudoku places digits in the margins of the grid. Each outside digit must appear in one of the first three cells (the nearest box) of the row or column it points to. No standard given digits are provided inside the grid — all clues come from the margins. This creates an unusual form of Sudoku where the initial constraints come from outside the grid entirely.
At a Glance
| Constraint type | Outside Clues |
| Typical givens | 28–36 given + 4×9 outside clues |
| Difficulty rating | ★★★☆☆ 3/5 |
| Avg. solve time — Easy | 8 min |
| Avg. solve time — Medium | 18 min |
| Avg. solve time — Hard | 36 min |
| Avg. solve time — Expert | 65 min |
How to Solve Outside Sudoku
| Technique | What it does | Level |
|---|---|---|
| Clue-Zone Mapping | Each outside digit must appear in the nearest 3 cells of its row or column. Map all outside clues to their zones immediately. | Beginner |
| Cross-Side Reasoning | If left clue digit X must be in cols 1–3, and right clue digit X is in the same row, that row already places X — the other side confirms its column. | Intermediate |
| Box-Side Interaction | An outside clue for a row interacts with the box containing cols 1–3. If the row's box is heavily constrained, the outside digit's position may be forced. | Intermediate |
| Digit Elimination from Clues | When a clue digit is placed in the zone, eliminate it from the rest of the zone row/col using standard Sudoku logic. | Intermediate |
| Dual-Side Chains | Combine left and right clues for the same row: both digits restrict the same three columns from opposite ends, leaving the middle box fully determined. | Advanced |
Average Solve Times
Easy
8 min
Medium
18 min
Hard
36 min
Expert
65 min
Frequently Asked Questions
What is Outside Sudoku?
Outside Sudoku is a variant where digits appear outside the grid's borders, one or more per row and per column. Each outside digit must appear somewhere within the first three cells of the row or column it points into (the nearest three to that outside clue). Standard Sudoku rules apply throughout.
How far into the grid do outside clues reach?
Each outside clue constrains only the first three cells of its row or column — the three cells nearest to where the clue is placed. A clue on the left side of row 5 means that digit must be in column 1, 2, or 3 of row 5. A clue on the top of column 4 means that digit must be in row 1, 2, or 3 of column 4.
Can an outside digit appear in any of the three cells?
Yes — the clue only guarantees the digit is somewhere in those first three cells, not which one. When multiple outside clues constrain the same three-cell window, their interactions can pin specific cells very precisely. Cross-referencing horizontal and vertical outside clues is the primary solving technique.
Is Outside Sudoku hard to learn?
The rule is simple but the deductions require careful accounting of which digits must appear in which windows. Easy puzzles are accessible for Sudoku players of all levels. Harder puzzles demand systematic tracking of all outside constraints simultaneously across every border.
What is the best first move in Outside Sudoku?
Find rows or columns where outside clues constrain all three cells in the first window. If three different clues each point to the same window, those three cells are fully determined in terms of which digits they contain (though not necessarily in which order). This is the fastest path to early placements.
How long does Outside Sudoku take to solve?
Easy puzzles take 8–18 minutes. Medium puzzles run 18–35 minutes. Hard puzzles average 35–65 minutes and expert puzzles can exceed 90 minutes. The key variable is how many outside clues are provided and how tightly they constrain each three-cell window.