Hardness
Convert ppm to grains per gallon
Water reports often list hardness in ppm. Softeners are rated in grains per gallon.
Your water
Start fromppm
Hardness5.8 gpgModerately hard
The math
- 100 ppm ÷ 17.1 = 5.8 grains per gallon
- USGS category: moderately hard (61 to 120 ppm)
The formula
grains per gallon = ppm (mg/L as calcium carbonate) ÷ 17.1USGS hardness scale
| Category | ppm |
|---|---|
| Soft | 0 to 60 |
| Moderately hard | 61 to 120 |
| Hard | 121 to 180 |
| Very hard | Over 180 |
Hardness is only one measure. Check your disinfectant too.