Measure a 27-inch square on a piece of heavy weight cardboard. Use the pencil to clearly mark the measurements.
Use the box cutter to cut along the marked lines, cutting out the square.
Use the ruler or tape measure to divide the square into three equal segments. Each will be 9 inches wide. Draw the two lines with the pencil.
Measure the center section of cardboard, marking it with the pencil 13.5 inches across the width of the middle third.
Use the box cutter to cut half way up each of the lines that divides the cardboard into thirds. Do not cut past the half-way mark on the middle section.
Fold the two outer sections inward to create a vertical "hinge" effect.
Fold the middle section upward on the line marked across its center. This creates a horizontal "hinge" effect.
Lie the board flat with its "hinged" flaps facing upward.
Center a shirt front side down on the cardboard. Smooth the arms out across the width of the board.
Fold the left flap in, then back out. This will fold the sleeve to the back side of the shirt.
Fold the right flap in, then back out. This will fold the sleeve to the back side of the shirt.
Fold the lower half of the middle section up, then back down. This folds up the bottom portion of the shirt and completes the folding process. Remove the shirt and store.