The normal Sudoku rules still apply. The trick is working out where the 1 and 9 go, because once you know the crusts, you know exactly which cells the clue is about.
Sandwich Sudoku rules in 30 seconds
- 1Every row, column and 3×3 box contains 1–9 exactly once.
- 2A clue beside a row or column is the sum of the digits between its 1 and its 9.
- 3The 1 and the 9 themselves are never counted.
- 4It doesn't matter whether the 1 or the 9 comes first.
See it on a board
Watch: how to play Sandwich Sudoku
Still not sure? Some puzzles click faster when you see them solved. This 10-minute video from Steven Scott shows Sandwich Sudoku in action.
Reading a clue
If part of a row reads 1 → 3 → 7 → 9, the filling is 3 + 7 = 10, so the row's clue is 10. The order of the crusts doesn't matter: 9 → 4 → 6 → 1 is also a sandwich of 10.
A row or column without a clue has no sandwich restriction, but it still has to follow the normal rules.
The extreme clues
- 0 means nothing is between them, so the 1 and 9 sit side by side.
- 35 is the biggest possible: 2+3+4+5+6+7+8 = 35, so the 1 and 9 are at the two ends of the line.
- Small clues force a short filling. The 1 can never be inside a sandwich, so a clue of 2 is a lone 2, a clue of 3 is a lone 3, and a clue of 5 is a lone 5 or 2 + 3.
Worked example: the remaining sum
- 1A row's clue is 18, and the 1 and 9 are three cells apart, so the filling is three cells.
- 2Two of those cells are already 5 and 6.
- 318 − 5 − 6 = 7, so the last filling cell must be 7.
Sandwich Sudoku tips and strategies
Place the crusts first
Look for 1s and 9s. Once both are known in a line, the filling is fixed and the clue becomes a simple sum.
Use the 35 ceiling
The seven digits other than 1 and 9 always total 35. A big clue means most of the line is filling; a small one means the crusts are close together.
Count the space
How many cells fit between the crusts limits which combinations can reach the clue.
Subtract known filling
Take away digits already known inside the sandwich and solve for what's left.
Common mistakes to avoid
- Adding the 1 or the 9 into the sum.
- Counting cells outside the crusts.
- Assuming the 1 has to come before the 9.
Play Sandwich Sudoku in 10+ Number Puzzles
- Clues sit outside every row and column they apply to.
- Use Notes to test where the 1 and 9 can go before committing.
- Auto Notes fills candidates from the Sudoku rules and the sandwich clues.
- You have 3 lives. A wrong digit costs one.
- Five difficulty levels, each a ladder of stages from Easy to Genius.
- Go online for free: ranked 1v1 duels, rooms where you race, co-op or play in teams, and tournaments.
- 27 more puzzle types in the same app, and online play never costs coins.
Sandwich Sudoku FAQ
What does a 0 clue mean in Sandwich Sudoku?
There are no digits between the 1 and the 9, so they sit next to each other in that row or column.
What is the largest possible sandwich clue?
35, when the 1 and 9 are at opposite ends of the line and all seven other digits are inside.
Are the 1 and 9 included in the sandwich sum?
No. Only the digits strictly between them count.
