Dry gallon measure of approximately the same size, though the dry gallon is a bit bigger. 1 dry gallon ≈ 1.163 647 fluid gallons Its implicit value in the US system was originally one eighth of the Winchester bushel, which was a cylindrical measure of 18.5 inches in diameter and 8 inches in depth. That made the dry gallon a non-terminating number of cubic inches, an irrational number whose value with the first six digits after the decimal point was 268.802521 ( cubic inches ≈ ). The bushel was later defined to be exactly 2150.42 cubic inches, making the dry gallon exactly
Grains per gallon Grains per gallon The grain per gallon (gpg) is a unit of water hardness defined as 1 grain (64.8 milligrams) of calcium carbonate dissolved in 1 US gallon of water (3.785412 L). It translates into 1 part in about 58,000 parts of water or 17.1 parts per million (ppm). Also called Clark degree (in terms of an imperial gallon). Calcium and magnesium ions present as sulfates, chlorides, carbonates and bicarbonates cause water to be hard. Water chemists measure water impurities in parts per million (ppm). For understandability, hardness ordinarily is expressed in grains of hardness per gallon of water (gpg).