Plumbing Calculator
Water Hardness Converter
Use our free water hardness converter to quickly translate between Grains per Gallon (GPG), Parts per Million (PPM), and mg/L. This is an essential step when sizing a water softener or testing your water supply.
Table of Contents
Hardness Value
Conversions
Equivalent water hardness levels
GPG
0
PPM (mg/L)
0
mmol/L
0
Hardness Classification: Hard
Water Hardness Conversions
Grains per Gallon (GPG) = mg/L ÷ 17.1
Parts per Million (PPM) = mg/L
mg/L = GPG × 17.1
mg/L = Milligrams per Liter, exactly equivalent to Parts per Million (PPM).
GPG = Grains per Gallon, standard measurement used for sizing water softeners.
17.1 = The exact conversion factor between GPG and mg/L (or PPM).
Water Hardness Scale
| Classification | mg/L or PPM | Grains/Gallon (GPG) |
|---|---|---|
| Soft | 0 - 60 | 0 - 3.5 |
| Moderately Hard | 61 - 120 | 3.5 - 7.0 |
| Hard | 121 - 180 | 7.0 - 10.5 |
| Very Hard | Over 180 | Over 10.5 |