Water Hardness Converter
Convert laboratory hardness readings from parts per million (ppm) into grains per gallon (gpg) for quick comparison with plumbing guidelines and water softener manuals. The calculation divides ppm by 17.118, the accepted conversion factor for calcium carbonate.
For water quality guidance only; confirm results with professional testing.
Examples
- A municipal report showing 140 ppm equals 8.18 gpg (moderately hard).
- Well water at 320 ppm converts to 18.69 gpg (very hard).
- Softened water tested at 40 ppm corresponds to 2.34 gpg (soft).
FAQ
What is water hardness?
It measures dissolved minerals like calcium and magnesium, expressed as calcium carbonate.
How do I convert ppm to gpg?
Divide the ppm value by 17.118.
Does a higher gpg mean harder water?
Yes, larger gpg values indicate harder water.
Can this calculator handle very high values?
Yes, but residential water usually stays below 30 gpg.
Why do some labs report hardness in mg/L?
Milligrams per liter is numerically equal to ppm for water samples, so you can enter mg/L values directly into the converter.
Additional Information
- 1 grain per gallon equals 17.118 ppm as calcium carbonate.
- Soft water is generally below 3 gpg, 3–7 gpg is moderately hard, 7–10 gpg is hard, and anything above 10 gpg is very hard.
- Tracking hardness helps choose the right softener setting, prevent scale, and extend appliance life.
- If you need to convert gpg back to ppm, multiply by 17.118.