Skip to main content

Independent, evidence-based water education · Reviewed for 2026

Quality & Testing · Tool

Water Hardness Calculator

Convert a water hardness reading between mg/L, grains per gallon and German degrees — and see which standard hardness band it falls into.

4.8 (231) Free & private — runs in your browser

Classification follows widely used guidelines. Hardness itself is not a health risk — it mainly affects taste, appliances and lather.

Educational estimates only — not medical, engineering or professional advice.

Water hardness is measured in several different units depending on the country and the test kit used. The number on a test strip often means little until you know which unit it uses and how the result classifies.

Enter your reading, choose its unit, and this calculator converts to all three common scales and tells you whether your water is soft, moderately hard, hard or very hard.

How to use this tool

Three units are supported:

  • mg/L (ppm as CaCO₃) — the most common laboratory unit in the UK, EU and many other regions.
  • Grains per gallon (gpg) — widely used in North America, particularly on water-softener packaging.
  • German degrees (°dH) — common in central Europe.

The classification thresholds (soft, moderately hard, hard, very hard) follow broadly accepted guidelines expressed in mg/L.

A little background

Hard water contains higher concentrations of dissolved calcium and magnesium minerals. It can leave scale on kettles and pipes and reduces soap lather, but it is not a health risk — some evidence suggests it may even provide a small dietary mineral contribution.

If you are reading about hardness and filtration options, our hard water vs soft water guide separates the facts from the myths.

Tool FAQ

Hard water is not considered a health risk. The WHO notes no convincing evidence of harm from consuming hard water, and some studies suggest a modest cardiovascular benefit from the calcium and magnesium it contains.

Parts per million (ppm) in a hardness context means the same as mg/L when the reference substance is calcium carbonate (CaCO₃). The terms are used interchangeably.

Common approaches include ion-exchange water softeners (which replace calcium and magnesium with sodium), and some filter types. Boiling removes temporary hardness caused by bicarbonates but not permanent hardness.

This varies enormously by region. Water in areas with chalk or limestone geology tends to be hard (above 150 mg/L), while water from upland reservoirs is often soft (below 60 mg/L).

Yes, noticeably so for many people. Hard water often has a slightly mineral or fresh taste, while very soft water can taste flat or slightly sweet. Personal preference varies.
4.8 / 5Based on 231 reader ratings
Was this helpful? Rate it: