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Hardness Converter (dGH / dKH / ppm)

Convert between degrees of hardness and ppm for general hardness (GH) or carbonate hardness (KH).

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Your reading

GH and KH measure different things

General hardness (GH) reflects dissolved calcium and magnesium; carbonate hardness (KH) reflects buffering capacity against pH swings -- a test kit result in one doesn't tell you the other.

How this calculator works

Water hardness is commonly reported in two different units: degrees (°GH or °KH, the German degree scale) or ppm/mg per liter as calcium carbonate (CaCO3). The conversion factor is fixed: 1 degree equals 17.848 ppm, regardless of whether you're converting general hardness or carbonate hardness -- the degree-to-ppm math is the same, only what's being measured differs.

Where this number comes from

The 17.848 ppm-per-degree conversion is the standard German hardness degree (°dH) definition used throughout the aquarium hobby and water-testing industry.

Frequently asked questions

What's the difference between GH and KH?

GH (general hardness) measures dissolved calcium and magnesium, important for livestock and plant health. KH (carbonate hardness) measures buffering capacity -- how resistant your water is to pH swings. They're related but test for different things.

Why do some test kits report degrees and others ppm?

It varies by manufacturer and region -- German-style degrees (°dH) are common in the aquarium hobby, while some test kits report directly in ppm. This converter translates between them.

Is a higher GH always better?

Not necessarily -- the right GH depends on what you're keeping. Many South American soft-water fish and plants prefer low GH, while African rift lake cichlids typically want high GH.

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