White Clear Round Brilliant Loose Cubic Zirconia, size and quality choice

White Clear Round Brilliant Cut Cubic Zirconia 

AAA - Good quality
AAAAA - Excellent quality, 
AAAAAA - Highest quality, sparkles the most, used for gold Jewellery

Height
Each cz has a height that is 62% of the width of the stone.  This is so that the patter of the pavilion reflects back out of the face of the stone to give it sparkle.

Please note, the stones are measured from edge to edge (diameter), so small sizes such as 1mm will be tiny, please make sure you choose the correct size.  When unpacking these small sizes, they can bounce around and get easily lost.  They are packed in a grip sealed bag wrapped in two layers of tissue, it is best to unpack these on a tray and unfold the paper slowly to stop any bouncing out and getting lost.

For Sizing 
If you need to know the size of a setting, then the only way to be sure is to put a stone in place to see if it fits the setting.  For the 1 of each size listing, this goes through every size starting from 0.7mm up to 2mm, 16 different sizes.  If you get the unlabeled stones, you will have to put the stones in order from smallest to biggest, this needs magnification to see the difference in size.  If replacing non precious synthetic stones like glass or cz, then it is likely the stone you need will be a multiple of 0.5, eg 1mm, 1.5mm or 2mm, but not always.  If you are replacing diamonds or other precious gemstones, then the sizes are often odd sizes, like 1.2mm or 1.9mm.

The 3 options for sizing are:

Every size in 6A quality up to 2mm in steps of 0.1mm (16 stones) Labelled or unlabeled
3A stones for common sizes 1mm - 4mm in steps of 0.5 (7 stones)

Quality

All stones are 8.5 mohs, will keep their colour and will not fade over time.  The quality is a measurement of how good the finished stone looks, how well it returns light and how accurately it is cut, the AAAAA and AAAAAA stones are cut from the highest quality material to make sure they sparkle as much as possible.  The AAAAA and AAAAAA stones are diamond simulants, these are used in gold jewellery in shop windows to simulate real diamonds, when viewed under a hearts and arrows viewer they show a hearts and arrows pattern which shows they are perfectly cut.

The A rating of CZ is not an official standard of measurement, so it is possible that AAA stones from one supplier will be better than AAAAAA from another.  I have been selling cz for 15 years and buy from gem cutters who grade their cz stones accurately.  AAA used to be the highest quality diamond simulants, so should not look bad today.