Square face shape
A visible turn at the jaw and similar widths.
How to recognize the outline
Look at the forehead, outer cheeks and jaw corners in a front-facing reflection. The square sketch keeps substantial width into the lower face. A recognizable turn beside the chin is often easier to see than any difference in overall length.
Square or triangle?
Start at the temples and trace downward. On a square outline the sides keep roughly similar width. On a triangle they open out toward the jaw. Hair covering the temples makes that comparison harder, so tuck it aside first. See the triangle sketch.
What to check when trying glasses
Try a fine curved rim beside a straight brow. Keep the outside edges equally wide. The curve crosses the angles you traced, while a straighter line repeats their direction.
A haircut trial in the mirror
Compare a straight front edge that finishes near the jaw with a swept piece that ends below it. You can pin the same section at two lengths before deciding whether to ask for a cut.
Compare your outline in the free face shape finder or ask friends to choose between two of your looks.