[grin|smile] from ear to ear

(of a person) to look extremely happy and satisfied

The idiom "grin from ear to ear" or "smile from ear to ear" suggests a broad and joyful smile that stretches across a person's face, from one ear to the other. The origin of this phrase is quite literal, as it describes the physical appearance of a very wide and happy smile, which naturally extends to the ears.

When Jane received the news of her promotion, she was grinning from ear to ear all day long.
As the couple exchanged their wedding vows, they smiled from ear to ear, radiating their happiness.
After winning the championship, the athlete was grinning from ear to ear during the awards ceremony.
Seeing her childhood friend after many years, Sarah was smiling from ear to ear, overwhelmed with joy and nostalgia.
The children couldn't hide their excitement on Christmas morning, as they smiled from ear to ear while opening their gifts.