Smile/grin/beam from ear to ear
Definition 1 of 1
Pro Tip 1/3Strong Happiness
Use it to express intense joy, delight, or satisfaction in casual situations. 
He couldn't stop smiling from ear to ear on his wedding day.
Pro Tip 2/3Not Literal
The phrase is a figure of speech and doesn't mean someone's smile literally extends to their ears. 
After the concert, she was beaming from ear to ear.
Pro Tip 3/3Positive Context
It's used in joyful scenarios. Avoid in sad or neutral contexts. 
After hearing the good news, he grinned from ear to ear.