GRAINS PER GALLON (GPG)
\ɡɹˈe͡ɪnz pɜː ɡˈalən d͡ʒˌiːpˌiːd͡ʒˈiː], \ɡɹˈeɪnz pɜː ɡˈalən dʒˌiːpˌiːdʒˈiː], \ɡ_ɹ_ˈeɪ_n_z p_ɜː ɡ_ˈa_l_ə_n__ dʒ_ˌiː_p_ˌiː_dʒ_ˈiː]\
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Water hardness as a measured unit. 1 grain (64.8 milligrams) of calcium carbonate dissolved in 1 US gallon of water equals one GPG. It figures out to be 14.3 parts per million (PPM) or 1 part in 70,000 parts of water. Known also as Clark degree. Also refer to hard water.
By Henry Campbell Black
