How to Convert Water Hardness in mg/L to GPG

Water may contain dissolved minerals that harden it.
••• Jupiterimages/Comstock/Getty Images

The quantity of dissolved calcium and magnesium polyvalent cations dissolved in a sample of water determine its hardness. Cations enter the water as it percolates through calcareous rocks such as limestone. Dissolved cations alter the properties of water, changing the way it reacts with other chemicals, including detergents and soaps. Hard water contains high levels of cation, compared with soft water, which contains low levels. Concentrations of cations in water are expressed in grains per gallon (GPG), or in milligrams per liter (mg/L).

    Establish the hardness value for the water in mg/L. Enter the value into a calculator and then check that you have entered the value accurately.

    Divide the value by 17.2, the conversion factor to convert from mg/L to GPG. The conversion factor is accurate to one decimal place, so round the result to one decimal place too. The result is the water hardness expressed in grains per gallon, or GPG.

    Check for errors. Multiply your answer by 17.1. If the result is neither equal to nor very close to the original value in mg/L, there was an error in your calculations. Repeat the conversion process.


    • To convert from GPG to mg/L, multiply by 17.1

      Milligrams per liter is the same as parts per million. There are 1 million milligrams in 1 kilogram, the mass of 1 liter of water.

Related Articles

How to Convert PPM to Grains in Water Hardness
Brine Vs. Conductivity
How to Find the Number of Representative Particles...
How to Convert Fluid Ounces of Water to Weight
How to Convert UG/mL to PPM
How to Convert MG to MEQ
How to Calculate the Mass of a Solid
How to Calculate Percent Solids by Weight
How to Calculate Concentration From Density
How to Convert Milligrams to Fluid Ounces
How to Convert PPM to MCG
How to Convert Tds to Conductivity
How to Calculate Solubilities
How to Dissolve Magnesium Chloride
What Color Would a Tester PH Paper Turn if Is Dipped...
Physical Properties of Urea
How to Change 1/4 to a Decimal Form
How to Find a Z Score