Flat stacking and managing steps
How to stack flat with no holes and steps of one row at most: where S and Z go, where to keep your well, and what to put first when you are unsure.
Techniques such as T-spins and perfect-clear stacking all assume that you can stack cleanly. The foundation of clean stacking is flat stacking: keep the surface of the board as flat as you can and stack without making holes. This page narrows flat stacking down to two things to watch: steps and holes.
A flat board can take any piece
You cannot choose which piece comes next. So a strong board is one where there is somewhere to put the piece, whichever one arrives. The flatter the surface, the more places you have to choose from.
Keep steps to one row
A difference in height along the surface is called a step. Many pieces fit neatly against a one-row step. At two rows fewer pieces fit, and a gap three or more rows deep can only be filled by the I piece.
| Surface | Pieces that fit without making a hole |
|---|---|
| Flat | O, I, T, L, J |
| One-row step | S, Z, T, L, J |
| Gap 1 wide, 2 deep | L, J (vertical), I |
| Gap 1 wide, 3 or more deep | I only |
S and Z need a one-row step
It may come as a surprise, but some pieces struggle on a perfectly flat board: S and Z. Lay either of them flat on level ground and there is always an empty cell under one side.
So the ideal is not “perfectly flat” but an almost flat board with one or two one-row steps. Stack with the intention of always keeping a spot somewhere for the next S or Z. When there is no step, hold the S or Z for later, build a step with another piece, and then place it.
Do not make holes
An empty cell covered by a block above it is called a hole. A row with a hole cannot be cleared until the blocks above it are cleared. Think of each hole as costing you one or two extra rows of work.
Before placing, get into the habit of checking whether any empty cell would be left under the piece. The ghost piece (the preview of where the piece will land) shows you the shape after placement. If a hole is unavoidable, choose the placement that makes only one hole, as close to the edge as possible.
One well only, at the edge
When you are going for Quads, leave exactly one well open for the I piece. The left or right edge is the best place for it. At the edge, the other nine columns work as one continuous flat surface. A well in the middle splits the surface into a left and a right half and makes the steps harder to manage. How to build one is explained step by step in “Stacking for Quads: leave one well open and clear with an I”.
Always keep it to one well. With two, one of them stays open until two I pieces have arrived. Note that when you are going for a perfect clear you leave no well at all and fit every piece inside four rows.
Priorities when you are unsure where to place
- Choose a spot that makes no hole.
- Choose a spot that keeps every step under two rows.
- Place low rather than high.
- Choose a placement that leaves a step for S and Z.
When no spot satisfies all four, think about using hold to place a different piece first. If that does not work either, give priority to the lower-numbered rule.