Why Medium Sudoku Suddenly Feels Harder

In our app, Medium Sudoku needs a move Easy never does: a digit with only one place left. What changes, when it happens on a real puzzle, and how to find it.

Updated 2026-11-06

What changes from Easy to Medium

In our app, a puzzle's level is set by the hardest step it needs. Easy puzzles never need more than a square with one digit left. Medium puzzles need the hidden single: for 100.0% of them it is the hardest step. They also start with fewer digits, 36 instead of 51, so there is more to work out.

You feel it on the clock. The median Easy game our players win without a hint takes about 3 minutes; on Medium, about 7.

What each Sudoku difficulty level asks of you →

The moment it happens

This is the first Medium puzzle from our printable Sudoku, with 36 digits given. Filling in every square that has only one digit left adds 14 digits, shown in blue, and then there are none left. The marked square could still hold 2 digits, so looking at it alone does not help. Looking at one digit does:

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Medium, sheet 1, puzzle 1: no square has only one digit left, and the marked square is the next move.

Row 1, column 1: 9. 9 has only one place left in its box.

How to find a hidden single

Pick a digit, for example 1.
Look at one box. Every row and column that already holds that digit rules out its squares in the box.
If only one empty square is left, the digit goes there.
Do the same with rows and columns, then move on to the next digit.
Each digit you place can open new moves, so go round the digits again.

Hidden Single →Medium Sudoku →

Tips for Medium

Scan by digit, not by square: that is the switch Medium asks for.
Start with a digit that is already placed many times: it has the fewest copies left to place.
You do not need notes yet. Every Medium puzzle in our app can be finished with these two kinds of single.
When Medium feels easy, Hard adds moves that rule out candidates, and that is where notes start to help.

Stuck on a Hard or Expert Sudoku? The Technique You Need Next →

Practice

Every Find the Mistake puzzle on this site has exactly one wrong digit, and you can play each board right on its page.

Play the puzzles →