The fastest way to get better at Sudoku is to look in the right order: start with the digits that are already common, scan a band of three boxes at a time, and go back to where you last placed a digit. When you need notes, write fewer of them. We tested these tips on all 150 of our levels, 50 at each difficulty, and the numbers below come from those tests.
These build on how to solve Sudoku. If you haven’t played before, start with the rules.
Solving tips
1. Start with the most common digit
A digit that’s already on the grid many times has the fewest places left, so it’s the most likely to have only one. At the start of a puzzle, find the digit given most often and scan every box for it first.
| Level | Most common digit has an only place | Least common digit has one |
|---|---|---|
| Easy | 94% of levels | 48% |
| Medium | 78% | 10% |
| Hard | 70% | 4% |
On a Hard puzzle, scanning for the rarest digit first almost never finds anything. Scanning for the commonest finds a move more than two times in three.
2. Scan two boxes out of three
The boxes come in three bands of three across, and three stacks of three down. Pick a digit and a band. If the digit is in two of the band’s boxes, those two are in different rows, so the third box’s digit must be in the row that’s left. Often that row has only one empty cell in the box.
This is the quickest form of finding the only place: you check three boxes at once, and you only need to look along rows. Do the same down each stack, looking along columns.
3. Go after the nearly full lines
A row, column or box with one gap left is a free digit. One with two gaps is nearly as good: you know the two digits it’s missing, and one of the two cells usually already sees one of them in its column or box. So look for the busiest lines and boxes as well as the commonest digits.
4. Finish off a digit
When seven or eight of a digit are already placed, the last one or two have nowhere much to go. Each missing one sits in the one row and column that don’t have it yet. In the game, the small number under each digit on the pad tells you how many are left to place.
5. Look where you just placed
Every digit you place changes its row, its column and its box, and that’s where it opens up new moves. On our Easy and Medium levels, three in four of the moves a placement opens are in its own row, column or box, and more than nine in ten are in its band or stack. Before scanning the whole grid again, check those.
6. Write fewer notes: Snyder notation
When the scanning dries up, you don’t have to fill in every note. A lighter method, known as Snyder notation, is to pencil a digit into a box only when it has exactly two places there.
On our Hard levels, at the point where scanning stops working, full notes come to about 127 marks on average. Snyder notation needs about 32, so roughly a quarter of the writing. And it still shows the patterns that matter most. A pair of marks in the same row or column of a box is pointing. Two digits marked in the same two cells of a box are a hidden pair.
7. Switch to full notes when you need them
Snyder notation can’t show a naked pair, and it doesn’t tell you when a cell is down to one digit. If you’re stuck with Snyder marks, fill in full notes, then start with the cells that have only two digits.
Tips for playing on PeerPuzzles
8. Tap a digit to see all its copies
Select a cell holding a digit and every copy of that digit on the grid lights up, along with the row, column and box of the selected cell. It turns tip 2 into a glance: tap a 6, and the boxes without one stand out at once.
9. Know what red means
A digit you enter turns red if it repeats a digit in its row, column or box. Red means the grid breaks a rule right now. It doesn’t work the other way round, though: a wrong digit that doesn’t repeat anything yet stays blue like any other. Only placing digits you’ve proved keeps the grid right.
10. Use the faster controls
- Keys 1–9 place digits; the arrow keys move around the grid.
- N turns notes on and off. When you place a digit, the game rubs it out of the notes in its row, column and box for you.
- U, or Ctrl/Cmd + Z, undoes a move. Backspace or 0 clears a cell.
- Entering the same digit again removes it.