Gravel/ˈɡrævəl/ is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel is categorized by the Udden-Wentworth scale into granular gravel (2 to 4mm or 0.079 to 0.157in) and pebble gravel (4 to 64mm or 0.2 to 2.5in). One cubic metre of gravel typically weighs about 1,800 kg (or a cubic yard weighs about 3,000 pounds).