Coffee grind size in microns — what each brew method actually wants
For years I thought 'fine' meant fine and 'coarse' meant coarse. Then I saw a particle-size distribution chart of my own grinder output and it changed how I brew.
Grind size is the single biggest variable in coffee that home brewers ignore. Water only has so long to pull soluble compounds out of a bean; the surface area you give it decides how much comes out. Too coarse and you get sour, thin, underdeveloped. Too fine and you get bitter, chalky, over-extracted. Both mistakes look identical if you only judge by the grinder dial.
The measurable quantity is the median particle diameter in micrometres — usually written µm, sometimes just 'microns'. A µm is one thousandth of a millimetre. Bakers who used to think in kg and cups had a similar moment when they discovered grams; this is that moment for coffee.
The rough ranges I use
Turkish: 40–100 µm. Genuinely powder. If you can feel individual grains between your fingers, it is too coarse.
Espresso: 200–300 µm. Feels like fine table salt. This is where a good burr grinder starts to matter, because a variance of 50 µm changes shot time by seconds.
Moka pot: 300–400 µm. Slightly coarser than espresso. Blade grinders can just about make this work if you shake the grinder while pulsing.
Pour-over (V60, Chemex): 500–700 µm. Feels like fine sand. Chemex sits at the top of the range because the paper is thicker and drains slower.
French press / cold brew: 800–1000 µm. Like coarse sea salt. Anything finer and the mesh does not hold it back — silty cup.
Why the numbers are so uneven
Grinders don't produce one size — they produce a distribution. A 'good' grinder outputs a tight bell curve around the target. A cheap one outputs a bimodal mess: some boulders and a pile of fines. The fines over-extract while the boulders under-extract, and you taste both at once. This is why the same recipe transports poorly across grinders even at 'the same setting'.
The µm number to chase is not the median — it is the standard deviation. A good hand grinder like a Kingrinder K6 does ~150 µm SD at pour-over settings. A basic blade grinder does 400+. Both label their output as 'medium'.
A cheap calibration trick
Sprinkle a small pile of your grind on a sheet of white paper next to a ruler that has a millimetre scale. Photograph it under bright light with your phone. Zoom in. Ten grains laid end-to-end that fill 6 mm means your median is ~600 µm — pour-over range. It is not a lab measurement, but it beats 'the dial says medium'.
Try the converters mentioned in this article
FAQ
Do burr grinders really matter that much?+
Yes, and mostly because of distribution width, not median accuracy. A tight distribution tastes cleaner even if the median is a hair off target.
Why does espresso need to be finer for lighter roasts?+
Lighter beans are denser and less soluble. Finer grind and higher temperature compensate for the harder-to-extract chemistry.
This article was written by The Turbo Unit Converter engineering desk (Applied metrology & engineering units) and last reviewed on 2026-07-20 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.