.80ct is definitely not small, but the size is definitely related to how big your ladies hands are. Do you know her ring size??? A .80ct ring will look huge on a size 4 finger, but it will look comparatively small on a size 9 finger. If she has a large finger, you may want to consider a ring with a halo or side stones in order to get better finger coverage. Also, where are you looking to purchase the ring from, and what is your budget? You may be able to get a better value from an online source rather than a brick and morter store, and thus, could afford a larger stone, if stone sizeis what you are concerned about...
I think it's a great size and I love the design. It's similar to mine and I'm very happy with it. The profile of the ring is very pretty.
I agree with tuffy, .80 is definitely not small. My diamond is a .76 and it's about 5.2mm since it's a square and not a round. My ring size is 6.25 (just to get over the knuckle, I'm probably closer to a 5.5 or 5.75 without the huge knuckles) and the .76 looks perfect on my hand.
Definitely listen to what the people here have to say about buying online! You can save a bunch of money and maybe with that money upgrade a bit
I agreed with the others. It all depends on how big or small your girlfriends fingers that will be the deciding factor. Is this diamond you are looking at GIA certified? I know when my fiance was looking for mine engagement ring, EGL and AGS seems a lot cheaper than GIA unless its a H & A. I would def. say you need to look online first and compare it to your local jewelers. I know for my center stone, our local jewelers wanted 8-10K more than what my fiance paid online. Also if you are in the chicago area, check our Jewelry's Row. They have a ton of diamonds available and they prices are very competitive. Have you thought about buying a ungraded diamond? if you want to go up in size that's something you may want to consider too...?
Good lucky. Make sure you come back and post pictures of the ring you have chosen.