The U.S. Department of Agriculture and the Soil Science Society of America define gravel as particles from in size, while the German scale (Atterburg) defines gravel as particles from in size. The U.S. Army Corps of Engineers defines gravel as particles under in size that are retained by a number 4 mesh, which has a mesh spacing of . ISO 14688 for soil engineering grades gravels as fine, medium, and coarse with ranges 2 mm to 6.3 mm to 20 mm to 63 mm.
The U.S. Department of Agriculture and the Soil Science Society of America define gravel as particles from in size, while the German scale (Atterburg) defines gravel as particles from in size The U.S. Army Corps of Engineers defines gravel as particles under in size that are retained by a number 4 mesh, which has a mesh spacing of . ISO 14688 for soil engineering grades gravels as fine medium, and coarse with ranges 2 mm to 6.3 mm to 20 mm to 63 mm.