180 ppm water hardness — 10.09 °dH, 10.52 gpg
180 ppm is the same water as 10.09 °dH in Germany, 18 °fH in France, 12.63 °e in England, 10.52 gpg in the United States and 1.798 mmol/L in the lab. On this chart’s scale it counts as hard.
- ppm (mg/L CaCO₃)
- 180 ppm
- German degree
- 10.09 °dH
- French degree
- 18 °fH
- English degree (Clark)
- 12.63 °e
- grains per US gallon
- 10.52 gpg
- millimoles per litre
- 1.798 mmol/L
Where soft ends and hard begins depends on the standard
The conversions are fixed; the grades are a choice. This chart draws its lines at the widely quoted 60, 120 and 180 ppm — meaning they are our approximation. The German detergent law, WRMG, draws its own at 1.5 and 2.5 mmol/L, that is 150.1 and 250.2 ppm, or 8.4 and 14 °dH. A 150 ppm water is therefore "hard" on this chart and "soft" under that law — the water did not change, the ruler did. Near a boundary, do not settle the question here: read the standard your appliance or your country actually uses.
- Grade on this charthard
- German WRMG grademedium
- Twice as hard360 ppm
- Half as hard90 ppm
- WRMG8.41 °dH · 14.02 °dH
Nearby cells
hard
Worth knowing
- ppm (mg/L CaCO₃) is the base, and every other unit is a fixed multiple of it.
- °dH is ppm ÷ 17.85, gpg is ppm ÷ 17.12, °fH is ppm ÷ 10, °e is ppm ÷ 14.25 and mmol/L is ppm ÷ 100.09.
- °dH and °fH both read "one degree per 10 mg/L", yet differ 1.78-fold because one counts CaO and the other CaCO₃.
- Grade boundaries differ between standards — the 60, 120 and 180 ppm on this chart are our chosen approximation.
Frequently asked questions
Q. How many °dH is 180 ppm?
10.09 °dH — ppm divided by 17.85. The same water reads 18 °fH in France, 12.63 °e in England, 10.52 gpg in the United States and 1.798 mmol/L as a molar concentration.
Q. Is 180 ppm soft or hard?
On this chart’s scale it is hard. Under the German WRMG, though, it is medium — that standard draws its lines elsewhere. Close to a boundary, go by whatever standard your appliance uses.
Q. What if the water were twice as hard?
It would be 360 ppm and every one of the six units would double exactly. Conversion is nothing but multiplication, so half of it, 90 ppm, halves every figure, and at 0 ppm every unit reads zero.