What is Suko?
Suko is a number-placement logic puzzle. In the classic 3x3 Suko puzzle, you place the numbers 1 to 9 so that each number appears once.
This online Suko game keeps the classic rules and adds larger 4x4 and 5x5 grids. The larger grids use the numbers 1 to 16 or 1 to 25 once each, which creates a deeper strategy puzzle without changing the basic idea.
- Use every number in the range exactly once.
- Match each 2x2 box sum shown between four cells.
- Match the total for every colour group.
- Starter numbers cannot be changed.
- Use logic from sums, colours and remaining numbers before guessing.
How to play Suko
Click or tap an empty square, then choose a number from the number bank. A number can only be used once, so every placement changes what remains available.
The small total markers sit at the corners between four cells. Each marker gives the sum of the surrounding 2x2 square. The colour panel gives the sum of all cells with that colour.
- Start with a 2x2 sum that already has one or two numbers placed.
- Compare overlapping 2x2 sums to find the difference between two cells.
- Use the colour totals to check whether a group needs low, middle or high numbers.
- Keep the number bank visible so you can see what has already been used.
- Use Check when you want feedback without revealing the whole puzzle.
Suko grid sizes and difficulties
The 3x3 board is the classic Suko size and is the best place to learn the rules. A 4x4 Suko puzzle adds more overlapping sums, and a 5x5 puzzle gives you a larger number bank with more long-range deduction.
Difficulty changes how many starter numbers appear. Easy Suko puzzles give you more fixed entries, medium puzzles leave more open space, and hard puzzles ask you to combine box sums with colour sums before the first move is obvious.
- 3x3: classic Suko with numbers 1 to 9.
- 4x4: a wider Suko strategy puzzle with numbers 1 to 16.
- 5x5: a larger challenge with numbers 1 to 25.
- Easy: friendlier openings and more anchors.
- Hard: fewer anchors and more deduction from totals.
Suko strategy tips
Look at overlapping totals. If two neighbouring 2x2 boxes share two cells, the difference between their totals tells you the difference between the two cells that do not overlap.
Colour totals are strongest when a colour group has only one or two empty cells left. Add the placed numbers in that colour, subtract from the colour total, and compare the result with the remaining number bank.
- Use subtraction rather than trial and error.
- Watch for colours that force mostly high or mostly low numbers.
- Compare adjacent box sums before filling isolated cells.
- Do not spend a large number unless a sum really needs it.
- Recheck used numbers after every confident placement.
How to solve Suko step by step
A Suko grid hides a single arrangement of the numbers, and the fastest way in is to combine the two kinds of clue rather than guess. Every cell holds a different number — 1 to 9 on a 3x3 board, 1 to 16 on a 4x4 and 1 to 25 on a 5x5 — so you always know exactly which numbers are still unplaced. Start with whichever clue is most constrained.
Colour sums are often the best opening. Find a colour group with only one or two empty cells, add the numbers already placed in it, and subtract from the colour total: the remainder must come from the numbers still in the bank. Then switch to the box totals, where two overlapping 2x2 squares usually share most of their cells, so the difference between their totals pins down a single cell.
- Remember the full number set: 1-9 (3x3), 1-16 (4x4) or 1-25 (5x5).
- Attack the colour group with the fewest empty cells first.
- Subtract the placed numbers from a colour total to see what is left.
- Compare two overlapping box totals to isolate the cell they do not share.
- Only test a candidate once the direct clues run dry.
The box totals and the centre-cell trick (3x3)
On the classic 3x3 board the four box totals overlap in a neat pattern, and seeing it gives you free deductions. The centre cell sits inside all four 2x2 squares, each edge cell sits in two, and each corner cell sits in only one. So if you add the four box totals together, the result counts the centre four times, every edge twice and every corner once.
Because the nine cells always total 45, that weighting lets arithmetic do the work. The four box totals added up, minus 45, equals the four edge cells plus three times the centre — often enough to pin the centre number on its own. The centre is the most valuable cell to solve early, because it feeds into every one of the four box clues.
Suko vs Sujiko: what's the difference?
Suko is often confused with Sujiko, and the two really are close relatives. Both fill a 3x3 grid with the numbers 1 to 9, and both use the circular box totals that give the sum of each surrounding 2x2 square. If you enjoy one, you will recognise the other instantly.
The difference is the colour clues. Sujiko gives you only the four box totals, so every deduction comes from those sums. Suko adds coloured groups of cells, each with its own target total, creating a second, independent layer of logic. That extra information makes Suko richer and lets it scale up to the larger 4x4 and 5x5 boards offered here.
Why play Suko online?
Playing Suko online makes the number bank, checking, hints and fresh puzzle generation immediate. You can switch from a quick 3x3 Suko puzzle to a harder 5x5 grid without printing or setting up a board.
This page is built as one evergreen Suko guide and game page, so players can learn the rules, practise strategy and start a new free Suko puzzle in the same place.