Laying out an 8×8 board
Eight is an awkward number. Here is the arithmetic of what fits beside what, why a 3 and a 4 in the same row leaves a hole, and how to keep a seam you can always close.
Eight is a slightly awkward width, and most of what makes a block puzzle board go bad is arithmetic that eight does not quite cooperate with. This page is about that arithmetic — what fits beside what, what is left over, and how to arrange things so the leftovers are usable.
Everything here assumes the standard rules: a square grid, rows and columns both clear when completely occupied, and nothing moves or settles after a clear. Cleared cells simply become empty and the rest of the board stays exactly where it was.
One thing to say plainly before the arithmetic starts. 8×8 is the convention this genre settled on, and it is the board most block puzzles you meet are built on — that is what this page works through. Blockwood itself is not square: its board is nine cells across and twelve deep, shaped for a phone held upright. Every habit below transfers, but two of the numbers change, and the last section before the checklist redoes them.
What actually fits across eight cells
Start with the largest thing in the game, the three-by-three square. Across a row of eight you can lay two of them side by side and have two columns spare. Three of them do not fit — that needs nine. So the honest capacity of the board, in terms of the biggest piece, is two three-by-three regions plus a two-wide strip, or one three-by-three plus a five-wide strip.
That is a useful mental image because it tells you how much slack you have. If you have let both potential three-by-three regions get contaminated with stray occupied cells, the biggest piece in the game has nowhere to go, and the board still looks perfectly healthy to a casual glance.
Run the same arithmetic downwards and it is the same number, because the board is square. Two three-by-three regions stacked vertically, two rows spare. A three-by-three plus a two-by-three rectangle in a column band uses six of the eight rows.
Parity, or why 3 plus 4 leaves a hole
Here is the trap that catches everyone. You have an empty row of eight. You place a three-long bar at the left end and a four-long bar next to it. That is seven cells. One cell remains at the right end, and to clear the row you now need exactly a single block, or a piece whose bottom edge is exactly one cell wide landing in exactly that column.
Single cells do come up — the smallest bar is one cell, and the rainbow piece is always a single — but you cannot count on one arriving before you need to spend that row on something else. Meanwhile the hole sits there keeping a whole row hostage.
The arithmetic worth memorising is which combinations sum cleanly to eight. Two fours. A five and a three. A four, a two and a two. Three, three, two. A three-by-three square’s three columns plus a five-long bar. When you are one piece from completing a row, count the gap before you place: if the gap you will leave is one cell wide and you have no single-cell piece in hand, consider putting the piece somewhere else entirely.
The same applies to the two-cell case. Leaving a gap of exactly two is far healthier than leaving one and one in different places, because two-long bars are common and two adjacent cells accept several pieces.
The nursery: reserve a corner and keep re-opening it
Pick one corner and treat the three-by-three region tucked into it as reserved space — a nursery. The rule is simple: nothing goes there unless placing it also clears a line immediately.
The point is not to keep it pristine forever. It will get used, and that is fine. The point is that you always know where your recovery space is, and that you re-open it deliberately rather than hoping. Re-opening means aiming a clear at it: if the nursery sits in the top-left, then completing the top row and the leftmost column both cut through it, and either one restores a chunk of it in a single move.
A corner is the best location for this precisely because corner space is otherwise the least flexible space on the board. You are giving a job to the cells that would have been hardest to use well anyway.
Seams: keep a line you can always close
A seam is a row or a column that is nearly complete and whose remaining gap is a shape you can reliably fill — two adjacent cells, or three, or a gap you know a bar will handle. It is your emergency exit. When a hand arrives and none of the placements look good, a live seam means at least one of the three pieces can be cashed in for a clear instead of being dumped somewhere damaging.
Try to keep one horizontal seam and one vertical seam alive at all times. Deliberately keep the gaps in them contiguous rather than scattered: a column missing cells in rows 2 and 3 is a seam, while a column missing cells in rows 2 and 6 is two separate problems.
Since a row and a column that are both one piece from completing can sometimes be closed by the same placement at their crossing cell, seams that intersect are worth setting up on purpose. When a placement completes a row and a column together, the crossing cell only settles once, and the score for clearing two lines at the same time is far more than twice the score for one.
Space that touches a wall versus space that touches four directions
Two empty regions of the same size are not equally valuable. An empty three-by-two block sitting in the middle of the board can be entered by a piece arriving from any side, and it lies across rows and columns that are all still live. The same three-by-two block jammed against the right edge can only be approached from three sides, and the rightmost column it occupies is a column you now have to complete from that edge inward.
So when you are choosing what to sacrifice, sacrifice the wall-adjacent space and keep the interior. The general shape of a well-managed board is a filled frame with an open core — the opposite of what most people build, because most people fill the middle first and end up with an empty border one cell wide, which accepts almost nothing but bars.
The same arithmetic on a 9×12 board
Blockwood widens the row from eight cells to nine and stretches the column from eight to twelve, and both changes are felt on the first hand. Nine divides by three, so three three-by-three regions lie across a row exactly, with nothing left over — the width stops fighting the largest piece in the game. Twelve divides by three and by four, so a column band takes four three-by-three regions cleanly. The stubborn two-column remainder that eight forces on you is simply not there.
The parity trap survives the move, with different sums. Combinations that close a row of nine exactly: three threes; a five and a four; a four, a three and a two; three, three, two and one. The trap is the same shape as before — a three and a five leave one cell, and so do two fours — so the habit does not change: count the remainder before you place, and prefer to leave a gap of two over a gap of one.
What genuinely changes is the price of a column. A row costs nine cells and a column costs twelve, a third more, so on this board the horizontal clear is the cheap one and the vertical clear is the opportunity you take when the board offers it rather than the one you plan around. Keep a seam alive in both directions if you can; if you can only keep one, keep the horizontal one.
A layout checklist
- Is there still a three-by-three region anywhere, in any orientation? If not, the largest piece in the game is currently unplaceable.
- Am I about to leave a one-cell gap in an otherwise finished row? Count before placing.
- Is my nursery corner intact, or do I have a clear lined up that cuts through it?
- Do I have one row and one column that are each within one convenient piece of completing?
- Is my empty space contiguous, or has it become a scatter of separate pockets?
- Am I filling the middle when an edge would have taken the same piece?
None of this requires counting cells precisely under pressure, because there is no pressure — nothing falls and no clock runs. The arithmetic is available to you for as long as you want it.
Frequently asked questions
How many 3×3 squares fit on an 8×8 board?
Two side by side, with two columns left over, or two stacked vertically with two rows left over. Three do not fit in a line because that would need nine cells. Knowing that number tells you how much slack you actually have for the largest piece in the game.
Why does filling a row with a 3 and a 4 cause problems?
Because three plus four is seven, and the row is eight wide, so you leave a gap exactly one cell across. That row can then only be completed by a single-cell piece or by a piece whose edge lines up exactly, and you may wait a long time for one. Count the remainder before you place.
Which corner should I reserve?
It genuinely does not matter which one, only that you pick one and stay consistent. Consistency is the value: you always know where your recovery space is, and you know which row and which column to aim a clear at in order to re-open it.
Is it better to keep the board flat or to keep it contiguous?
Contiguous. Flatness matters in games where pieces fall from above, but here nothing falls and nothing compacts after a clear, so height is meaningless. What matters is whether your empty cells form one connected region that could accept a large piece.
Is Blockwood an 8×8 board?
No. 8×8 is the genre convention, but Blockwood’s board is nine cells across and twelve deep, so it fills an upright phone screen. The arithmetic on this page transfers with two changes: nine divides by three, so three 3×3 regions fit across a row exactly, and a column costs twelve cells against a row’s nine, which makes rows the cheaper clear.
Try it on a real board
Blockwood is a wood block puzzle on a nine-wide, twelve-tall board, with nothing falling and no dealt dead ends — every hand is checked against the board you actually have before it reaches you. Endless mode, timed mode, hand-built levels and a daily challenge. Free, offline, no ads and no account.