Here's the tutorial for the square patchwork coaster. :)
As with the triangle ones, you can make these any size you like but make sure to cut your fabrics into 5 identical squares.
For my project, my squares are 6x6 inches. Fold the patchwork pieces lengthwise into rectangles, Place the rectangles' folded sides to the centre of the back square (dark green fabric) and the raw edges to the outer perimeter.
Seam allowance is 1/4 inch (about 0.5cm). After sewing securely aound the perimeter, turn the coaster inside out and iron flat.
Hope you will give this and the triangle patchwork coasters a try!
Happy Sewing! :)