Perfect Clear basics

The conditions for a perfect clear, how to think about 4-line PCs and how to read leftover shapes.

September 30, 2026

A perfect clear (PC) happens when a line clear removes every block from the board, leaving it completely empty. It gives a large bonus and, in versus play, a powerful attack, which is why it is a standard opening strategy. This page covers the basics you need to start stacking for perfect clears.

Count the cells

The board is ten cells wide. For a four-line PC you have to fill 10 × 4 = 40 cells. A piece is four cells, so exactly ten pieces must fill the four rows. Two lines are 20 cells (five pieces); three lines are 30 cells (7.5 pieces, so impossible).

Always keep track of whether the remaining empty cells are a multiple of four. A single hole that no piece can fill ends the PC attempt on the spot.

The red single-cell hole cannot be filled by any piece; the four-line PC is already impossible.

The leftover

With 7-bag, the first seven pieces fill 28 cells and leave 12 of the 40. If the first three pieces of the next bag fill those 12 cells, you get a four-line PC. The shape of those 12 cells is called the leftover (or residual).

A good leftover is one that many different piece combinations can fill. You do not know which three pieces the new bag will deliver first, so a leftover that only works with one specific trio has a low success rate.

A 3×4 rectangle on the right can be filled by three vertical I pieces, by I + L + J and by several other combinations.

A 2×4 rectangle looks tidy, but it can only be filled by two copies of the same piece (I·I, O·O, L·L or J·J). A single 7-bag cycle never contains two of the same piece, so it only works across a bag boundary.

Core principles

1. Keep every region a multiple of four

Empty areas separated by walls or by fully filled columns must each contain a multiple of four cells. Fully filled columns are the important separators to watch.

The left region has 6 + 4 + 3 = 13 cells. Not a multiple of four, so this cannot become a PC as it stands.

2. Stack flat and low

Everything has to fit within four rows, so local towers reduce your options. Keep steps to one row and the surface as flat as possible. S and Z pieces sit flat naturally on one-row steps.

3. Plan with the visible pieces

With five previews and hold you can see up to seven pieces. Work out how far the visible pieces get you, and treat the missing piece as a probability based on what the next bag may bring.

Eight cells left. The active T fits nowhere, so hold it, place the next O first (dotted) and finish with the I that follows. Hold makes this possible.

Learn the spin-ins

Some leftover shapes cannot be entered by dropping straight down; the piece has to be rotated in using wall kicks. The most common are T spin-ins and L/J spin-ins. Rotation mechanics are explained in “Wall-kick rotation basics”.

A T spin-in: it will not fall into place, but rotating on the way down puts it on the dotted cells.

How to practise

Start with drills that have few cells left, such as “4-piece leftover, 6 pieces to finish”.
Before placing, count the remaining cells and build a plan with the visible pieces.
After a failure, review which piece order would have worked and where the multiple-of-four rule broke.

The Perfect Clear practice mode shows a success rate that accounts for the visible pieces, the hold piece and the distribution of the pieces still hidden in the bag. The recommended placement is drawn as a dotted outline, and the full solution and hold reasoning are listed. Begin with high-probability boards and follow the solution until the shapes feel familiar.

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