Water Hardness Converter & PPM to dH Calculator (UK Tool)

Water Hardness Converter – Convert PPM, dH, °TH, Clarke & gpg (UK Calculator)

Convert water hardness between every unit used in the UK and Europe. Enter a value in PPM (mg/L as CaCO₃), English °Clarke, German °dH, French °TH, US grains per gallon (gpg) or mmol/L, and this tool returns all the others instantly. UK water companies usually report hardness in mg/L (ppm) or °Clarke, while appliance manuals and test kits often use German °dH — so a quick conversion makes it easy to compare your reading against any guide. Below the converter you’ll find a full reference table and the hardness classification bands used in the UK.

Water hardness

Hardness converter

Enter a hardness reading in any unit — we’ll convert it instantly.

Total hardness needs both: ppm CaCO₃ = 2.497 × Ca + 4.118 × Mg

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UK hardness scale

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