Coffee Calculators
Water Hardness & Alkalinity Calculator
https://www.coffeesizing.com/calculators/water-hardness-alkalinity/
Estimate only — not a cupping score, a water lab or a roast profile. Confirm on a test brew.
Water Hardness & Alkalinity Calculator
GH is calcium plus magnesium; KH is alkalinity, mostly bicarbonate. Coffee charts bounce between ppm as CaCO₃ and German degrees (°dH). One °dH is about 17.8 ppm. The GH:KH ratio is a quick sanity check — very high KH with low GH is a different cup than the reverse.
Inputs
Results
- GH
- 4.49°dH
- KH
- 2.25°dH
- GH:KH ratio
- 2.00
Recommended gear
Water filter pitcher
If GH is café-scale high, filter or RO then rebuild with a recipe. Measuring without a plan just documents the scale.
Typical range: $20–$50
Descaling powder
Hard GH still crusts boilers. Know the °dH, then set a descaling interval from shots and volume.
Typical range: $10–$25
Espresso machine
Scale kills heating elements. Match water to the machine’s warranty GH, not only to flavour charts.
Typical range: $400–$2,500
Calculation method
German degrees are ppm as CaCO₃ divided by 17.8. 80 ppm GH is about 4.5 °dH; 40 ppm KH is about 2.2 °dH. The ratio is GH ppm over KH ppm (2.00 at the defaults). Kits that already speak °dH do not need this page — recipes that speak ppm do.
Exact formula
ghDegrees = ghPpm / 17.8. khDegrees = khPpm / 17.8. ratio = ghPpm / khPpm (0 if KH is 0). Limits: Test-strip accuracy, calcium vs magnesium split and non-carbonate hardness omitted; ppm is as CaCO₃.
Flavour vs machine
Soft, low-KH water can taste bright and still be kind to a boiler. Very hard GH tastes dull and bills you in heating elements. Pick a lane.
Frequently asked questions
ppm CaCO₃ vs ppm Ca?
Coffee recipes almost always mean CaCO₃ equivalent. A lab ppm as calcium ion is a different number. Do not mix them.
Is 2:1 GH:KH ideal?
It is a common specialty starting shape, not a law. Some espresso waters run closer to 1:1. Taste and scale risk both matter.
US grains?
One grain per gallon is 17.1 ppm, almost a German degree. Close, not identical. Convert from ppm if you can.
More in this topic
All tools in this topicWater chemistry
Barista Water Recipe Calculator
Build brewing water from target GH and KH as ppm CaCO₃. Get Epsom salt and baking soda in milligrams and grams for a chosen volume.
Water chemistry
Coffee Buffer & Acidity Calculator
Compare water KH to brew TDS for a simple buffer index and whether acidity is likely muted. Alkalinity fights acids; it does not erase roast.
Water chemistry
Descaling Frequency Calculator
Estimate days and shots until a descale from water hardness, daily shots and boiler volume. A maintenance schedule, not a plumber.
Water chemistry
Water Bypass Calculator
Add bypass water to a brewed batch to hit a lower target TDS. Beverage mass goes up; extraction yield of the grounds stays where it was.