2 millimeters: Largest size a grain of sand can be (above that it’s gravel)

0.125 millimeters: Smallest size sand can be (below that it’s silt)

3: Numbered of featured “Sand Grains of the Month” at The Virtual Sandbox Museum of World Sands

10x: Magnification recommended for viewing sand

Source: The Virtual Sandbox Museum of World Sands at www.jaster.20m.com