Demi Lovato's Engagement Ring Worth at Least $2.5 Million, Over 10 Carats

If Demi Lovato's engagement ring looked expensive, that's only because it's worth more than $2 million, and comes with some razzle-dazzle too ... TMZ has learned.

Sources with knowledge tell us ... Demi's ring would cost the average Joe off the street anywhere between $2.5 million and $5 million -- and that's due to the fact that it's a very special cut from a very well-regarded celebrity jeweler in Hollywood ... Peter Marco.

We're told Demi's diamond is an emerald cut that was hand set in platinum, and flanked on all sides by smaller (only relatively) trapezoid-shaped diamonds designs. All told, our sources say the rock comes in at well over 10 carats ... maybe even as much 20!!! No one's spilling the exact weight.

We're told Demi's fiance, Max Ehrich, spent a lot of time to make sure the design was unique -- namely, he really wanted the elongated stone for Demi. We're told he and Marco went back and forth with different side stones and angles until the ring was just right.

Their engagement came after just a few months of dating ... albeit quarantine-dating. Demi and Max first got together in March, and they've been quarantining/vacationing all over Cali since then.

After Max put a ring on it ... Demi said, "I knew I loved you the moment I met you," adding, "I’m ecstatic to start a family and life with you. I love you forever my baby. My partner. Here’s to our future!!!!"