Quick and Easy Buying Guide
Carat weight: 1 carat = 200 milligrams = 6.5 mm diameter. Doubling weight doesn't double diameter.
Diamond clarity: FL/IF/VVS/VS = super expensive, near perfect. SI = best value if you can check a photo for obvious inclusions (defects).
Color: D-G = colorless, expensive, only if you have money to burn. H-J = best value. Can go lower in gold metal settings than white metal.
Cut: Better cut ratings let more light into a diamond, making it sparkle more. Very important property, don't skimp here.
Set a budget and minimum cut (Premium). Go J color for gold and I/H for white metals. Go searching for SI1/SI2 clarity diamonds at James Allen. Pick a diamond with small/no inclusions. Choose a ring setting and buy it risk-free (60-day returns).
1.63 Carat Princess Shape Diamond Sizes on Hand
This article includes a handy illustration that gives you the apparent size of a 1.63 carat weight princess shape diamond, when it's actually on a typical woman's hand. A princess shape diamond with a carat weight of 1.63 is usually about 7.1 mm long on the side; this can of course vary depending on cut.
If you've got a ring in your possession and you know the size, you can compare it to the US size six ring pictured - this will assist you in getting a concrete idea of the diamond size shown in the photo.
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The dimensions of a female hand can vary hugely - being in public is evidence enough - so this picture can only provide the apparent diamond size for a typical size ring.
Think about the ratio between the width and length of a finger - this ratio can play an important role in how large and appropriate a diamond appears when it's slipped in a ring onto the hand. If you're a male trying to work out the right diamond size to get your partner, don't forget that the diamond will usually look much bigger on the hands of a woman, which are typically smaller.