mm to mm. in the united states, sand is commonly divided into five sub-categories based on size: very fine sand ( ⁄ – ⁄ mm diameter), fine sand ( ⁄ mm – ⁄ mm), medium sand ( ⁄ mm – ⁄ mm), coarse sand ( ⁄ mm – mm), and very coarse sand ( mm – mm). these sizes are based on the krumbein phi scale...