A common basis of reporting water analysis in the United States and Canada. One grain per U.S. gallon equals 17.1 milligrams per liter or 17.1 ppm. One grain per Imperial gallon equals 14.3 milligrams per liter or 14.3 ppm. One grain is 1/7000 pounds or 0.0647 grams.

An expression of concentration, usually the 'hardness of water'. One grain per gallon is equivalent to 17.1 parts per million.

A common basis for reporting water analyses in the US and Canada. One grain per US gallon equals 17.12 milligrams per liter (mg/L) or parts per million (ppm).

A common basis for reporting water analyses in the United States and Canada; one grain per U.S. gallon equals 17.12 milligrams per liter (mg/1) or parts per million (ppm). One grain per British (Imperial) gallon equals 14.3 milligrams per liter or parts per million.