What is a grind index? BrewMark's 0–100 grind scale explained

Why can't you copy a dial number from one grinder to another?

Because dial numbers are a manufacturer's own labels, not a unit of size. Röststätte puts it directly: "there is no fixed standard between the manufacturers of coffee grinders," and "a '4' on a coffee grinder does not mean that the same grind will be achieved with another grinder."

Honest Coffee Guide makes the same point, noting that settings come as numbers, decimals, clicks, degrees and letters. The two Baratza Encore models show how far apart they can be, even on the same 40-step dial. Baratza's Encore manual suggests 15 for a Hario V60. The Encore ESP manual suggests 25.

The ESP is built differently on purpose. Its manual explains that settings 1–20 make small changes for espresso, while 21–40 make "relatively larger changes" for filter. The Encore vs Encore ESP comparison shows both dials on the shared scale.

How does BrewMark build the 0–100 scale?

It fixes five reference points and fits each grinder's dial to them. The anchors are the same for every grinder.

When a grinder has no recorded moka or French press anchor, BrewMark fills it in by straight-line interpolation between its neighbors. The moka point is placed 15/40 of the way from espresso to filter, and the French press point halfway from filter to coarse.

Converting works in two steps. Your grinder's setting is turned into an index number, then that index is turned into the other grinder's setting. The result is rounded to one decimal place and kept inside the target grinder's minimum and maximum.

Why does BrewMark use curves for some grinders and straight lines for others?

Conical burr grinders get a smooth curve, and flat burr or unlabeled grinders get straight lines between anchors. The curve is a monotone cubic spline, a method called Fritsch–Carlson interpolation.

"Monotone" is the important part. The curve bends smoothly through each anchor but never overshoots, so a finer index always gives a finer or equal setting. For the reverse direction, setting to index, BrewMark solves the curve numerically.

A flat burr grinder, such as the Fellow Ode Gen 2 in BrewMark's catalog, is mapped with straight segments between its anchors instead.

What does a conversion look like?

In BrewMark's catalog, the Baratza Encore has its filter anchor at 20, so setting 20 reads as index 40. The Comandante C40 MK4 has its filter anchor at 26 clicks, so the same index lands on 26 clicks. Comandante's own FAQ suggests 18–35 clicks for pour-over.

Between anchors the curve does the work. Encore setting 15 reads as index 27.5, which BrewMark converts to about 20 clicks on the C40 MK4.

Is grind index 40 the right setting for my V60?

Not exactly. Index 40 is BrewMark's filter-medium reference point, not a recipe. Recipes start near it and then move finer or coarser for the brewer, dose and taste.

BrewMark's recipe adaptation shifts the index before converting it, for example for the filter paper you use or your taste preferences. The adjusted index is then translated to your dial.

How accurate is the grind index?

It is as accurate as each grinder's anchors, and BrewMark says which ones have been checked. On each grinder page, anchors checked against a published per-method chart are marked verified. The rest are marked unverified, and some anchors are interpolated from a family pattern rather than read off a chart.

The index also has limits by design. It maps nominal dial positions, so it cannot see a grinder whose zero point has drifted. It does not describe burr quality or the spread of particle sizes. Two grinders at the same index can still taste different, so use the converted setting as a starting point and adjust by taste.