Hardness numbers you can act on
gpg, ppm, and what to do after you test—before you buy a system. Clear metrics without the sales pitch.
Read & act
Where to go from this hub
Core Water guide plus the two tools that use the number. Not a buried archive list.
Hardness units at a glance
Same facts as the core guide—kept here so you can convert gpg/ppm without leaving the hub.
gpg vs ppm
Grains per gallon (gpg) is the usual unit for sizing softeners. Parts per million (ppm) shows up on many kits and reports. Convert once—then size.
- 1 gpg ≈ 17.1 ppm (mg/L as CaCO₃)
- ppm ÷ 17.1 ≈ gpg
Hardness ranges
Ranges are common homeowner rules of thumb—not a medical or lab certificate.
Testing at home
Drop kits and strips both exist. Pick a kit you’ll actually use—then write down gpg before you shop.
How numbers drive gear
Three steps from a test result to a system decision.
Beyond the grains
Calcium and magnesium don’t just sit in the glass—they leave scale on fixtures and in heaters. That’s the homeowner version of the chemistry, without a lab pitch.
Published water guides
Live articles in this hub—appear here when draft is false.
Leave Water when you’re ready
Numbers are one hub. Systems, essentials, and problems are the next doors.