Water Hardness Calculator
Convert your water hardness between ppm (mg/L) and grains per gallon (gpg), and see how hard your water is — then get the right softener.
How water hardness is measured
1 grain per gallon (gpg) = 17.1 ppm (mg/L). Most US homes fall between 3 and 20 gpg. Above 7 gpg you'll see scale, spotting and dry skin — a softener pays for itself in appliance life.
Required: download your full results & recommendation as a PDF to save and share.
Frequently asked questions
How do I convert ppm to grains per gallon?
Divide ppm by 17.1. For example, 171 ppm = 10 gpg. Our calculator does it instantly both ways.
What is considered hard water?
Above about 7 gpg (120 ppm) is hard, and above 10.5 gpg (180 ppm) is very hard. At those levels a water softener is strongly recommended.
How do I find my water hardness?
Check your municipal water report, use a test strip, or send a well sample to a lab. Then enter the number here to convert and classify it.