We graded 4,000 sudokus: how often each technique is needed

The short answer

• Singles do almost everything. Of 161,712 steps, 76.8% were naked singles and 21% hidden singles. Every other technique together: 2.2%.
• Medium means a naked pair, most of the time. 74.4% of medium puzzles needed a naked pair, 24.6% needed pointing and 4.9% a box-line move.
• Hard means a hidden pair, and sometimes an X-wing. 76.1% of hard puzzles needed a hidden pair and 25% an X-wing.
• Expert puzzles beat the techniques on purpose. In all 1,000, logic filled 36.1% of the empty squares on average before it ran out.
• The levels hold. 3,999 of 4,000 puzzles graded at the level they were made for; one hard puzzle came out medium.

Read across a row to see how a technique climbs with the level. Hidden singles are needed in 2.7% of easy puzzles but every medium and hard one, because an easy grid nearly always has a square with only one number left somewhere, and our solver takes that first.

Singles do almost all the work

A sudoku is filled one square at a time, and each square is placed by a single: either the square has one number left (a naked single) or a number has one square left in a row, column or box (a hidden single). The bigger techniques never place a number themselves. They rule candidates out until a single appears. So even in the hardest puzzle, almost every step is a single, and the clever move is needed once or twice.

A hard puzzle took 52.8 steps on average, and one that needed a hidden pair used it 1.2 times. That's why a hard sudoku feels easy for long stretches and then stops dead: you're looking for one hidden pair or one X-wing, and the rest follows.

What each level needs

Easy

Singles only, by design: 97.3% of easy puzzles never needed more than a naked single, and the other 2.7% needed a hidden single at some point. They start with 40 or 41 numbers and take about 41 steps.

Medium

The hardest step was a naked pair in 70.9% of medium puzzles, pointing in 24.2% and box-line in 4.9%. They start with 32 to 37 numbers (32.4 on average).

Hard

The hardest step was a hidden pair in 74.9% of hard puzzles and an X-wing in 25%. Along the way 26.1% also used a naked pair and 16.1% pointing. They start with 27 to 31 numbers.

Expert

Every expert puzzle is one our solver can't finish, so somewhere it needs a guess or a technique beyond the X-wing. They start with 24 to 28 numbers. Before stalling, 41.6% of them still needed something beyond singles.

Expert: where logic runs out

Half the expert puzzles let logic fill 36% or more of the empty squares before it stalls. The best got 80% of the way; one stalled before a single number could be placed.

When logic stalls, people test a square: pick one with two candidates, try one of them, and see whether it leads to a clash. Our solver tells you when you've reached that point, and can show you the rest of the answer.

How we did it

The puzzles. Suvi makes each day's sudoku from that day's date, so everyone gets the same puzzle. We ran the same code with the same seeds for 1,000 days in a row, from October 15, 2026 (the first day of the archive) to July 10, 2029, at each of the four levels: 4,000 puzzles. No puzzle was picked or left out. Days still to come are in the sample too; none of their grids is shown here.

The solver. Every puzzle was graded by our own solver, the one in the sudoku solver and behind the game's Hint button. It knows these techniques, easiest first: naked single, hidden single, naked pair, pointing, box-line, hidden pair, X-wing. At every step it uses the easiest one that leads to a number being placed, and only climbs to a harder one when the easier ones find nothing.

What "needed" and "hardest" mean. A technique was needed if the solver used it at least once on its way through the puzzle. A puzzle's hardest technique is the highest rung it had to climb at any step, and that is what sets its level on Suvi: singles only is easy; a naked pair, pointing or box-line is medium; a hidden pair or X-wing is hard; stalling is expert.

A check. We counted each puzzle twice, once with the step-by-step solver above and once with the grader that sets the daily's level. They agreed on the hardest technique for 4,000 of 4,000 puzzles and on the number of steps for 4,000.

What this doesn't tell you

• It's our solver's route, not yours. It always looks for a naked single before a hidden single, so it counts more naked singles than a person might, who often spots the hidden single first. Your own route through a puzzle can use different techniques at different moments.
• These are Suvi's puzzles. Our generator aims each level at a set of techniques and a range of starting numbers, so the levels differ by design. Puzzles from a newspaper or a book are graded differently, and the numbers here don't describe them.
• The ladder stops at the X-wing. Some expert puzzles would fall to a bigger technique (a swordfish, a chain) without any guessing. Our solver doesn't know those, so it calls them all expert.
• Starting numbers follow the level. Expert puzzles start with fewer numbers than easy ones, but that's because our generator aims at a range for each level; the count alone doesn't make a puzzle hard.

Try it yourself

• Sudoku solver: paste any puzzle and watch each step, with the technique named and explained.
• Today's Sudoku, at all four levels: start with medium to meet your first naked pair, or try hard for a hidden pair.
• Sudoku techniques: our guide to every technique above, with worked examples.
• Killer Sudoku, when you want a different kind of logic.

Written by Brasslight Games from our own data · Updated November 1, 2026 · The numbers come from forge/sudoku-stats.mjs, run on 4,000 puzzles.