Conical vs flat burr grinders: right on average, a poor guide to your grinder

Every page that ranks for this question tells the same story. Conical burrs make two sizes of particle, and that gives you body; flat burrs make one size, and that gives you clarity. Conical runs slower, cooler and quieter and keeps less coffee inside; flat runs faster, hotter and louder and hoards it. So: flat for light roasts and pour-over, conical for dark roasts and milk.

I read twenty-odd of those pages. None of them shows a measurement. When I went looking for the measurements, the largest set I could find — 24 espresso grinders measured in a Swiss university lab, plus a blind tasting of the best nine by four professional tasters — says something less tidy. The rule holds on average. It tells you very little about any one grinder you might buy. In that blind final, a conical grinder came first. The other conical came last.

Below: what was actually measured, the two different questions the rule mixes up, the heat, noise and retention figures from a ten-grinder test, what the companies that make both kinds of burr say about the difference, and a table of common grinders by burr shape.

Affiliate links. Some links below go to Amazon. If you buy through one I earn a commission at no extra cost to you, and it never changes which product gets named or what the measurements say. Full disclosure.

Seven claims, checked

Here is the rule as the ranking pages give it, set against the numbers:

The last row is about the market, not the physics, and the noise row holds up. The rest is where the story comes apart — and the first row is the one everything else hangs on.

Every burr grinder makes fines

“Unimodal” is the word doing the damage. Taken literally, it means a grind with one peak — every particle close to one size. No burr grinder that has been measured does that, flat or conical. The peer-reviewed paper on how temperature changes the grind used a flat-burr Mahlkönig EK43, and once its particles are weighted by surface area, in the paper’s words, “the data appears distinctly bimodal”: a fines peak and a main peak. When Jonathan Gagné fitted the distributions from 24 espresso grinders, every one of them had a fines peak, and its position moved by no more than about 8 µm from grinder to grinder.

So the real question is never whether a grinder makes fines. It is how many, at a given size. That is what the one large dataset measures. Kaffeemacher, a Swiss and German coffee company that runs cafés and barista courses, put 24 espresso grinders through the same coffee; Marco Wellinger at the Zurich University of Applied Sciences measured about 300 samples on a Camsizer X2, an instrument that photographs particles as they fall; and Gagné, an astrophysicist who writes about coffee physics, analysed them. It is not peer-reviewed. It is public, with its method shown, and it is the only one of its size I found.

Gagné compared every grinder at the same median particle size, 340 µm, on two measures: how much of the grind was fines under 100 µm, and how far the coarse particles spread into boulders. His finding on burr shape is one sentence, and every word of it matters:

“Conical burrs appear on average less unimodal and less uniform, although there is a large overlap meaning that one can easily find a specific flat burr that is less unimodal and less uniform than a specific conical burr.”

On average, in other words, the rule is right. For choosing a grinder, the overlap is the part that counts. Ten of the 24 grinders were conical, and the four cheapest in the whole series — the €80–150 group — were all conical. In Gagné’s chart, one of those four, Tchibo’s own-brand grinder with a built-in scale, sits among the three most uniform grinders of the 24, next to two commercial flat-burr machines. Another of the four, a Graef, is the least uniform of all. Same shape, same price band, opposite ends of the chart.

The data has limits: one coffee, one unit of each grinder, and — Gagné’s own caveat — no way to know whether each grinder’s burrs were well aligned, which could move both measures. The same analysis also found that larger flat burrs were not systematically more uniform and that rotation speed showed no clear pattern, which I went through in the piece on grind size and flavour.

Same grind size, or same shot?

Here is where the rule quietly swaps one question for another.

“Conicals make more fines” is true at the same grind size — Gagné’s fixed 340 µm median. But nobody brews at a fixed median. You grind until the shot runs in the time you want, and Gagné’s other finding is that doing so is mostly an adjustment of fines: “when we dial in espresso, we are dialling in the amount fines more so than we are dialling in the average size of coarse particles.” A grinder that makes few fines builds little resistance, so you grind it finer to compensate — and finer means more fines. He found the effect overshoots: grinders that make fewer fines “actually require us to reach a slightly larger amount of fines per gram of coffee in our puck to be dialled in.”

The clearest demonstration I found is Kaffeemacher’s 2025 comparison of ten single-dose grinders at €500–1,000. Nine have flat burrs. The Niche Zero is, in the testers’ words, “the only grinder in this comparison built around conical burrs.” Each was dialled in for the same espresso recipe, and a sample of each espresso grind was measured:

The puck from the conical grinder held the fewest fines in the field, by a wide margin, and it was ground the coarsest. That is not a contradiction of the 24-grinder average — it is the other question. Ask about the grinder, and the conicals lean towards fines. Ask about the puck in your portafilter, and in this field the conical’s had the fewest.

Then look at how the testers described the cups. The Niche Zero’s was “velvety, creamy, body-forward.” Two flat-burr grinders, the DF83V and the Profitec, sat on the body side too — “high body and punch,” “dense, sensuous” — and they had the most fines. The two Timemores, with the narrowest peaks, were “extreme clarity.” So body turned up at both ends of the fines scale, and nobody has published why. Gagné says as much: the finding makes it “harder to understand why the perceived body is lower” in shots from low-fines burrs, since those pucks likely hold more fines per gram, not fewer.

“Conical, therefore more fines, therefore body” is a chain with a link missing, and no one has measured the missing link.

The blind final

The same 24-grinder series ended with a tasting. The best nine from the six price groups went into a final, judged blind by four experienced tasters Kaffeemacher invited — Q Graders among them, and a two-time Swiss barista champion who has judged at the World Barista Championship. Each grinder got 20 minutes and its own recipe, set by the baristas, and two espressos over two days: Apas, a natural Brazil they describe as nutty, chocolatey and forgiving, and Doña Margarita, a lighter, more complex natural from Nicaragua. The published points:

Look at the Forté’s row first. It won the darker coffee and came last on the lighter one — the roast the rule says a flat burr should flatter. The conical Niche Zero won that lighter coffee by almost seven points and the whole final by more than eight. And the only other conical in the final, the Sage Smart Grinder Pro, finished last overall. One conical first, one conical last: the shape did not sort them.

This is one team, four tasters, two coffees and published totals whose scoring scale the page does not explain. It is not peer-reviewed, and it is not the last word. It is the only blind tasting of this size I found, and it gives the rule nothing to stand on.

The two other tastings I found point the same way, more quietly. America’s Test Kitchen sieved and tasted ten grinders with coffee professionals from Counter Culture and George Howell, and wrote: “In our taste test, we didn’t find discernible differences between coffee made with grounds from a conical burr grinder and that from a flat burr grinder.” (All of its top picks were conical; its winner was one of Baratza’s.) And a hobbyist who pulled 29 pairs of shots from a Niche Zero and a flat-burr grinder across 15 roasts found no taste difference that was statistically significant — his flat burrs, he noted himself, were not aligned, and he was the only taster.

What I could not find is a peer-reviewed study that puts conical and flat burrs head to head. I searched the scholarly literature for one; the nearest was a 2026 preprint that used one grinder of each shape to test a way of summarising particle sizes, not to compare the shapes. On the question the whole search is asking, the published science is silent.

Heat, noise and what stays inside

The same ten-grinder comparison measured the three things the rule is most confident about. Noise was taken 20 cm from the grinder during a continuous 250 g grind; temperature in the grounds after five 18 g doses 20 seconds apart; retention by weighing what is left per dose.

Noise is the claim that survives. The conical was the quietest — by 2.0 dB over the nearest flat-burr grinder, while the loudest and quietest flats were 16.7 dB apart. That is a gap between flat-burr grinders eight times the size of the gap between the shapes. If quiet matters to you, the number to look for is the grinder’s, not its burr shape.

Heat does not survive. The conical came fourth-coolest of ten; the coolest grinder in the test had flat burrs and ran 5 °C cooler than it. And the testers’ own verdict on the whole spread was that it “is completely uncritical and stays within a very narrow range. No flavor impact is to be expected from it.” For scale, the SCA’s grinder standard allows a filter grinder to warm the coffee by up to 10 °C. Warm burrs do change a grind — cold beans grind finer and narrower, which is one of the two things that move your grind without touching the dial — but at home, a few doses a day, the burr shape is not what decides it.

Retention survives only as a statement about grind paths. The two grinders that kept the least coffee in this field, 0.1 g per dose, were the flat-burr Timemores, and the testers put it down to “the vertical burr arrangement, a direct grinding path.” Gravity helps whatever is mounted so that coffee falls through it; Mahlkönig says it mounts the flat burrs of its EK43 vertically for exactly that reason. And conical grinders can hoard too: Kaffeemacher weighed 4 to 5 g, with higher peaks, in a Graef CM800. The SCA’s own grinder standard allows 1.5 g of a 30 g dose on average, and the test is simple enough to run on your own grinder with a scale that reads 0.1 g.

Rotation speed is the grain of truth under the heat and noise claims. Conical burrs do spin slower on average — Gagné’s data shows it, and Mazzer, which makes both, says so. But across the 24 grinders, rpm “does not correlate clearly” with how many fines or boulders a grinder makes. The one within-grinder observation I found comes from the testers: on a variable-speed grinder, they saw a narrower main peak at 500 rpm than at 1,600. That is a report from one grinder, not a published study — and in the ten-grinder field, every grinder with a speed dial had flat burrs.

Static, the other thing flat burrs are blamed for, has one peer-reviewed study behind it, and it used a single flat-burr grinder: the charge depended on the roast, the grind setting and, above all, the moisture left inside the beans, and burr shape was never compared. In the ten-grinder field, static was a problem on some flat-burr grinders and not on others.

What the companies that make both say

Mazzer, in Italy, has made grinders since 1948 and designs both conical and flat burrs in its own factory. Its answer to “what is the main difference?” is worth reading for what it leaves out:

“Whilst the conical burrs rotate at a lower speed than the flat burrs, they can achieve higher productivity levels than those of flat burrs with the same diameter. Due to the low grinding speed, the conical appliances ensure greater acoustic comfort. Furthermore, conical burrs wear much more slowly than flat burrs … Appliances with flat burrs offer greater reactivity to the adjustment change, due to the more compact grinding chamber.”

Speed, output, noise, wear and how quickly a change of setting shows up. Not fines, not clarity, not body. The one company I found that makes both kinds in its own factory does not claim the difference the internet is sure of.

Its wear figure is real, and irrelevant at home. Mazzer’s indicative service lives run from 300 kg to 1,800 kg for its flat burr sets, depending on model and coating, and 600–1,000 kg for its conicals. At 20 g of coffee a day, 300 kg is 41 years.

The other makers of both shapes blur the rule from the inside. Baratza describes its conical burrs as producing “balanced and delightfully sweet cups,” its steel flat burrs as “high-clarity” — and its 54 mm ceramic flat burrs as the choice “for anyone who love a full-bodied cup of coffee,” with “rounded, syrupy textures.” Two flat burr sets from one company, sold as opposites. A German maker of hand grinders sells its conical burr as “engineered for clarity.” Fellow sells its flat-burr Ode for brewing and states plainly that it “is not suitable for espresso,” while its espresso grinder, the Opus 2, is conical. Niche makes a conical grinder, the Zero, and a flat one, the Duo — which it designed around two burr sets, one for espresso and one for filter.

The makers of flat burrs only are the ones who state the rule as fact. Mahlkönig’s home grinder page says flat burrs “achieve a significantly higher proportion of particles with the same shape and size than conical burr grinders.” Turin contrasts “conical burr grinders that produce micro fines at espresso settings” with the “consistent, uniform grind” of its own flat-burr grinder. Neither shows a measurement, and the ten-grinder table above has flat-burr pucks carrying more fines than the conical’s.

What all of this points at is the burr set, not the shape: tooth geometry, the pre-breaker, coating, alignment, speed, the path to the exit. Gagné’s conclusion from the 24-grinder data was the same — “burr teeth geometry and coating appear much more important as driving factors” than size — and it is why two grinders of the same shape can land at opposite ends of a chart.

Buying for espresso

The rule’s espresso version — conical for body, flat for clarity — is the one the blind final argued with hardest, so set the shape aside and look at what the measurements did separate:

• Adjustment. Espresso lives in the last few microns. America’s Test Kitchen’s rule of thumb for an espresso grinder was “at least 40 settings and lots of finer options”; Kaffeemacher’s testers rate grinders on whether they return exactly to a setting after a big change. Stepless or finely stepped, and repeatable, matters more than cone or disc.
• The style you want. In the ten-grinder field, the flat burrs with the narrowest peaks gave “extreme clarity” and a puck the testers called fragile, prone to a slow build and then a sudden rush — a job for careful distribution and for watching for channeling. The conical was the forgiving, body-forward one; two flats were body-forward too. Choose a style from a grinder’s published results, not from its burr shape.
• What it keeps. If you single-dose, weigh it. The best and worst in the field were both flat.

And when a flat-burr maker writes that “dedicated espresso grinders almost universally feature flat burrs,” it leaves out a lot. Mazzer’s Robur S, a café espresso grinder, runs 71 mm conical burrs; Weber Workshops’ HG-2 hand grinder uses 83 mm conical burrs made by Mazzer. When you have your grinder, dialling it in is the same job whichever shape it is.

Buying for pour-over

Some of the people typing “conical vs flat” with “pour over” are asking a different question: the shape of the dripper. That one has a documented answer. The SCA’s brewer certification standard specifies one grind for cone-shaped baskets and a different one for flat-bottomed baskets, and the bands move by hundreds of microns — the detail is in the grind size chart piece.

For the burrs, the one laboratory that tests home grinders on filter coffee — the European Coffee Brewing Centre in Oslo, which sieves the grind, runs a six-kilogram endurance test and brews with the result — has approved both shapes. On its list today: the Grindersupreme, whose maker describes a conical burr, and six flat-burr grinders including the Wilfa Uniform and the Moccamaster KM5. What that seal does and does not tell you is in the piece on grinder certification.

Two more cautions from the data. A grinder’s ranking at espresso sizes need not carry over to filter sizes: in a set of hand grinders that Lance Hedrick measured by laser diffraction, Gagné found one that behaved like the high-fines grinder of the set at espresso sizes and like the low-fines one at coarser, filter sizes. And in the 24-grinder series, the testers’ two best results for filter coffee in one price group came from a flat-burr ECM and the conical Niche Zero. Flat burrs made for brewing exist — Fellow sells its Ode for exactly that — but no measurement I found says flat is the price of a good pour-over.

Common grinders, by burr shape

Burr shape and size are from each maker’s own page, read on 26 September 2026. The right-hand column gives the independent result on record, where there is one. No prices — they change, and this list is not a ranking.

Both hand grinders in the list are conical. On the evidence above, that is not a compromise to worry about.

What I would actually do

Take burr shape off the list. It is a real difference on average and a poor predictor for any one grinder, and the one company I found that makes both kinds says so by omission. The things that separated grinders in the measurements — adjustment, retention, noise, the particular burr set — are all on a spec sheet or in an independent test.

On a starter budget, for espresso and filter, I would buy the Encore ESP and not think about its shape again. It is the grinder America’s Test Kitchen chose after sieving and tasting ten; it has a dedicated espresso range of twenty settings; and it is conical, as were all of that test’s top picks — which, on the evidence here, is not the thing to worry about.

Spending more for espresso, pick a style, not a shape. The published measurements now map grinders from forgiving and body-forward to clear and fussy, and both shapes turn up at the forgiving end. Read the results for the grinder you are considering; ignore the adjective attached to its burrs.

For filter only, a flat burr made for brewing is a fine choice, and so is a good conical. If you want a third-party floor, the ECBC’s seal is the one that exists, and it has been given to both.

Whatever you buy, weigh what it keeps in the first week. Ten rounds of 30 g, beans in and grounds out, on a scale that reads 0.1 g. If it averages more than 1.5 g, it fails the SCA’s own bar — conical or flat.

The shape of the burrs is a real difference on average. It is not the difference you are buying.