Round vs Square Face: Look at the Jaw, Then the Whole Outline
A round face has a gently curved lower outline, while a square face has more noticeable jaw corners and a broader, more angular lower face. Both can look relatively wide compared with their length. That is why width alone is a poor way to tell them apart: compare the shape of the jaw and how its width relates to the forehead and cheeks.
Look for corners, not just broad cheeks
With your hair away from your face, follow the outline from the side of the cheek down toward the chin. Does it continue in a soft curve, or does it make a more distinct turn at the jaw?
Then check the upper face. A broad forehead paired with a broad, angular jaw supports a square description. A softer lower curve, with width concentrated around the cheeks, supports a round description. Keep those clues together; a single wide area does not describe the entire outline.
Why the hairstyle advice overlaps
Round and square faces are often given similar advice when the goal is to make the face appear longer: keep some forehead visible, avoid excessive fullness beside the cheeks, and consider lengths that extend below the chin.
A shared haircut recommendation does not make round and square the same face shape.
It means the recommendation is addressing a feature they can share: apparent width. Once you consider the jaw corners, the details of the cut can diverge.
Similar length, different ends
Keeping length and softening corners are separate jobs for a haircut.
For a round outline, a blunt edge can be considered when the aim is to introduce a more definite line. For a square outline, softer ends and curved framing can be considered when the aim is to make the jaw angles less prominent. These are styling options, not compulsory rules.
This also explains an apparent conflict around blunt cuts. A clean lower edge is not the same feature as thick, straight-across bangs. Nor does it specify where the cut ends. A bob that stops at the chin and carries considerable fullness beside the cheeks can emphasize width, even if a more defined edge is the effect you wanted.
The practical inference is to assess the edge, its height, and the fullness beside it separately. “Blunt” alone does not tell you how the whole haircut will frame your face.
A square jaw can be the feature you keep
Advice to soften a square face assumes that softer-looking angles are your goal. You may prefer to show them. An exposed jaw and a short cut can be a deliberate choice when that is the feature you enjoy.
The decision is whether to echo the jaw or soften its outline, not whether a square face needs fixing.
For your final comparison, keep two observations separate: whether the lower outline curves or turns at the jaw, and whether you want your hair to emphasize that shape. The first helps distinguish round from square. The second determines what you do with the distinction.