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BrewMarkBREWMARK

Owners’ readings

Measure Your Grind Size From a Photo

Photograph a pinch of grounds on white paper next to a coin. This page finds each particle, sizes it against the coin and gives D10, D50 and D90 in microns. It all runs in your browser: the photo never leaves your device.

Your grinder and setting

Take the photo

  1. Grind a few grams at the setting above.
  2. Sprinkle a pinch thinly over a sheet of plain white paper, so the particles sit apart and do not touch. A few hundred particles is enough; more is better as long as they stay separate.
  3. Put a coin flat on the paper beside the grounds, not on top of them.
  4. Photograph straight down, in bright even light without hard shadows, close enough that the paper fills the frame. Daylight from a window works well; avoid the flash.

The photo is analysed in this browser. It is never uploaded.

Mark the coin

Add a photo above and it will appear here.

Needs at least 200 separate particles. Method: the BrewMark Protocol, measurement.md.

Why measure

A grinder's dial numbers mean nothing outside that grinder. Particle size in microns does: 800 µm is 800 µm on any machine. BrewMark's grind index places grinders against each other from makers' charts and comparison today. Readings from owners, at known settings, are how that can move onto measured sizes.

Each submitted reading is held as pending and reviewed before it counts. One reading is a data point, not a verdict: burrs wear, units vary, and a photo has limits. Several owners measuring the same grinder is what makes a number worth using.

What a photo can and cannot see

Fines are undercounted
A particle needs a few pixels to be seen. Anything finer than about two pixels across is missed, so the finest end of the distribution reads low. The tool says where that floor is for your photo.
Touching particles merge
Two grounds that touch look like one bigger one. Long chains and outsized blobs are left out, but a pair that touches can slip through. Spread the grounds thinly.
Light and shadow matter
Hard shadows add to a particle’s size and glare takes away from it. Bright, even, indirect light gives the cleanest edges.
A photo is flat
Size comes from each particle’s outline seen from above, as the diameter of a circle of the same area. A flat flake can read larger than it would through a sieve.

Results are given by volume, the way laser diffraction and sieves report, so they can sit beside readings made those ways. A photo with fewer than 200 separate particles gets no reading.