Sandwich Sudoku Explained — Rules, Combinations and Strategy
Sandwich sudoku takes the 9×9 grid you already know and moves half the clues outside it. Beside each row and each column sits a single number: the sum of the digits that lie strictly between the 1 and the 9 in that line. A 0 means the 1 and the 9 are neighbours. A 35 means the whole run 2-3-4-5-6-7-8 is sandwiched between them. Everything else — every row, column and 3×3 box holding 1–9 exactly once — is unchanged. If you have been searching for sandwich sudoku explained without the usual wall of jargon, this page is the plain version: one daily grid seeded by date so everyone gets the same puzzle, unlimited Easy, Medium and Hard boards, a strategy section, and a complete sandwich sudoku combinations reference so you never have to guess a total again.
Sandwich Sudoku Rules
- Standard sudoku: each row, column and 3×3 box contains 1–9 exactly once.
- Outside clues: the small numbers in the tray above each column and left of each row are that line's sandwich total.
- The sandwich: in any line, find the cell holding the 1 and the cell holding the 9. Add up every digit strictly between them — that sum must equal the outside clue. The 1 and the 9 themselves are never counted.
- Zero is a real clue: a total of 0 means the 1 and the 9 sit in adjacent cells, which is often the most useful clue on the board.
- Unique solution: every board here is verified with a solver to have exactly one solution under sudoku rules plus all eighteen outside clues.
Worked example: if a row reads … 1 · 5 · 3 · 7 · 9 …, the digits strictly between the 1 and the 9 are 5, 3 and 7, so that row's outside clue is 15. Nothing else in the row counts toward the total.
Sandwich Sudoku Combinations Reference
The digits between the 1 and the 9 are always a subset of {2,3,4,5,6,7,8}, so a sandwich total can only run from 0 to 35. That sounds restrictive, but each total still has many possible subsets — and knowing which ones is the entire technique. Look up any total below, or read the full table.
🥪 Sandwich sudoku combination lookup
Full sandwich sudoku combinations table (all totals 0–35)
| Total | Possible digit sets between 1 and 9 | Cells needed |
|---|
Three totals are worth memorising outright. 0 forces the 1 and 9 to be adjacent. 35 forces every one of 2–8 between them, so nothing else in that line can be anything but the 1 and the 9. And the extremes 4 (just the digit 4) and 31 (just the digit 4 missing — i.e. 2,3,5,6,7,8) pin down the anchors instantly.
How to Solve Sandwich Sudoku — Five Steps
- Find the 1 and the 9 everywhere. These two digits are the anchors of every clue, and because each digit appears once per row, column and box, placing a 1 or a 9 immediately informs every line it touches. Solving for anchors first is the single biggest speed-up in the variant.
- Use the extreme totals. Any 0 tells you the 1 and 9 are adjacent, so those two cells are {1,9} in some order. Any 35 tells you the seven inner cells are exactly 2–8, which usually gives you a run of naked singles.
- Count the cells. If a total can only be made with a subset of two digits, then exactly three cells are between the anchors, so the 1 and 9 are four cells apart. Use the combination table to translate total → number of cells → anchor positions.
- Cross-reference rows against columns. A 9 placed in row 3 fixes the column clues that row shares. Sandwich puzzles cascade once the anchors are known, so work row/column pairs rather than grinding one direction.
- Combine overlaps with normal sudoku logic. Once the anchor positions are locked, the puzzle is a fairly ordinary 9×9 with more givens than usual. Naked and hidden singles, pointing and claiming all still apply exactly as in classic sudoku.
Difficulty Levels
- Easy: around 34 givens and generous outside clues. Ten to twenty minutes once the anchor habit clicks.
- Medium: around 28 givens, the daily default. Needs the combination table and careful candidate work.
- Hard: around 24 givens. Long anchor chains, minimal redundancy, and plenty of pencil marks.
Daily Puzzle, Streaks and the Leaderboard
The Daily grid is built by generating a complete valid grid, deriving its eighteen sandwich clues from that grid, then removing givens and verifying that exactly one solution survives — all in your browser, in about two milliseconds. Because the generator is seeded by the date, every player on the same date receives the same givens and the same outside clues, so comparing solve times actually means something. Finish today's board and your time joins the shared daily leaderboard Top 50.
After that, the Unlimited button gives you endless fresh verified puzzles at any difficulty. For other flavours of the same grid, try Killer Sudoku with cages and sums, Jigsaw Sudoku with irregular regions, Mini Sudoku for 5×5, 6×6 and 8×8 boards, or check a stubborn position with the Sudoku solver. The number games and logic puzzles hubs list everything else on the site.
Why Sandwich Sudoku Is So Satisfying
Most sudoku variants add a new constraint. Sandwich sudoku removes information from inside the grid and puts it outside, which means the clues are global rather than local — one outside number constrains seven cells you cannot see yet. That makes the first ten minutes feel like detective work and the last ten feel like a waterfall of placements. There is no arithmetic beyond addition, no guessing, and no hidden data: just rows, columns, boxes, and eighteen sums. Play it free, on any device, with no account.