The Crystals/Stones we sell are not calibrated. Chip Stones are what remains after the tumbling process of larger rough stones. The size/measurement of these stones is approximate, and falls within a size range. Since orders are filled using random scoops, you will receive larger and smaller stones, than the stated measurements. These stones are intended for crafting purposes, and we don't guarantee that you will receive any specific stone size, for use with any other purpose.