Cardi B's Engagement Ring from Offset is Worth Over Half Million Dollars (Details, pics)

Cardi B is definitely walking around with a fortune on her left hand ... because Offset definitely didn't skimp when he put a ring on it.

The Migos rapper dropped $550k on Cardi's engagement ring, which took a month and a half to make ... According to the owner of NYC's Pristine Jewelers. It came together just in time for Offset's live onstage proposal, but means he really must have been sweating during their brief breakup.

Cardi's shiny 8-carat stone's surrounded by 2 half-carat pear diamonds and 2 carats worth of pink and white stones. The ring's totally custom made in the raindrop shape Offset wanted.

It also worked out perfectly -- it was gathered that the ring was through with by the day of the Philly Powerhouse concert and he went to pick it up just hours before he proposed on stage.

As we reported ... Offset could get a big chunk of his ring money back -- he and Cardi B are wanted for a TV wedding special that could land the couple over a million dollar.