Grind size chart
Which grind for which brewer, from Turkish to cold brew.
Water Hardness Calculator
Convert between ppm, dH, fH, gH and mEq/L, and see whether your tap water is going to make good coffee or destroy your boiler.
water chemistry
Hardnessppm
ppm CaCO₃
120
dH (German)
6.7
fH (French)
12.0
gH (Grains)
7.0
mEq/L
2.40
0 soft60120180250+ hard
Moderately hard. Workable for filter coffee, but you will want to descale the kettle monthly and consider a softener for an espresso machine.
ClassificationModerately hard
Refractometer–free verdictAdequate
Scale risk (espresso)Medium
Descale interval~3 months
The conversion factors
| Unit | Equals | Meaning |
|---|---|---|
| 1 ppm CaCO₃ | 1 mg/L | Milligrams of calcium carbonate per litre. US and lab default. |
| 1 °dH | 17.85 ppm | German degrees. Common on European appliance specs. |
| 1 °fH | 10 ppm | French degrees. Used on most water utility reports in France. |
| 1 gpg | 17.1 ppm | Grains per US gallon. Standard in American softener marketing. |
| 1 mEq/L | 50 ppm | Milliequivalents. Used in water chemistry and SCAA discussions. |
What hardness does to coffee
Hardness is mostly calcium and magnesium. Both bind to flavour compounds during extraction — magnesium pulls out fruity acids, calcium pulls out heavier, bitter notes. Too little and the cup tastes flat and chalky; too much and the cup tastes dull and the machine furs up.
The practical band for brewing is 50–175 ppm. Below 50 the coffee tastes hollow. Above 175 you get scale in the boiler and a muddy cup. Specialty water recipes — SCA, Barista Hustle, Rao — all target roughly 1.5–2× the ideal alkalinity with around 70–80 ppm total hardness.
Scale is the real cost
At 250 ppm, an espresso machine on unfiltered tap water will scale visibly within weeks. Scale insulates the heating element, raises recovery time and eventually kills the boiler. If your water is over 150 ppm, a simple inline softener cartridge is cheaper than a service call.
Test your own water rather than trusting the utility report — hardness varies by street, and the report is often an annual average from a plant on the other side of town.
Frequently asked
What is the ideal water hardness for espresso?
Around 70–100 ppm total hardness with alkalinity near 40 ppm. That is soft enough to avoid scale and hard enough for the water to carry flavour compounds properly.
Is soft water better for coffee?
Only up to a point. Zero-hardness water — distilled or reverse osmosis — makes flat, lifeless coffee because there are no minerals to bind flavour. If you use RO water, remineralise it.
How do I test my water hardness at home?
A drop-count test kit is accurate to about 10 ppm and costs a few dollars. Cheap electronic TDS meters measure conductivity, not hardness, and will mislead you because they also count sodium and chloride.
Coffee ratio chart
Nine brew methods, dose and water in grams. Printable.
Basket size chart
Correct dose for every espresso basket size.
Water sorted? Now the shot.
Use the espresso ratio calculator to get your dose and yield in grams.