Whole Home Water GuideWater treatment tool
Water Hardness Converter
Convert a water hardness reading between grains per gallon and ppm, then read the standard soft to very hard classification band.
Screening estimate only.Confirm results with a certified water test and a water treatment professional before you buy or size equipment.
Screening result
Fine Print and Sources
Screening estimate only. These tools use only the values you enter and simple planning math. A certified water test and a water treatment professional are authoritative for final sizing, salt settings, and purchase decisions.
This converter uses the standard 1 grain per gallon equals 17.1 ppm as calcium carbonate relationship. The soft to very hard bands follow the widely used water hardness classification.
- USGS Water Science School, hardness of water: gives the water hardness classification bands used here in milligrams per liter as calcium carbonate.
- Water Quality Association, scale and hardness: describes grains per gallon as the common hardness unit, where 1 grain per gallon equals 17.1 ppm.