GPG to PPM Converter
Convert between grains per gallon (GPG) and parts per million (PPM) instantly. Get your water hardness classification.
Enter a value above to see the conversion.
The Conversion Formula
1 GPG = 17.1 PPM
GPG to PPM:
PPM = GPG × 17.1
PPM to GPG:
GPG = PPM ÷ 17.1
Understanding the Units
Grains per Gallon (GPG)
The traditional US unit for water hardness. One grain equals approximately 64.8 milligrams of calcium carbonate per gallon of water. Water treatment professionals and water softener manufacturers typically use GPG.
Parts per Million (PPM)
The metric equivalent, also expressed as milligrams per liter (mg/L). Scientific reports and international standards often use PPM. Municipal water quality reports may use either unit.
Both units measure the same thing: the concentration of dissolved calcium and magnesium minerals in water. Use whichever unit your test kit or water report provides.