Grinder listings state the burr shape as though its meaning is obvious. It is not, and the usual online summary — “flat burrs are more precise, conical burrs are cheaper” — is close enough to be misleading.
Both shapes are used in serious grinders at every price. The difference is in what the resulting grind is like, and that has consequences you can taste.
The mechanical difference
Conical burrs are a cone sitting inside a ring. Beans fall into the gap at the top, and gravity pulls them down through a channel that narrows until the particles are small enough to fall out the bottom.
Flat burrs are two parallel rings facing each other. Beans enter at the centre and are pushed outward by the rotation, getting progressively crushed until they exit at the edge.
Two consequences follow directly.
Conical burrs are gravity-fed, so they can turn slowly and still work. Slower rotation means less heat and, in most designs, quieter operation and lower retention of grounds between doses.
Flat burrs must generate enough centrifugal force to move coffee outward, so they turn faster. That means more heat and, historically, more grounds left inside the grinder between uses — the reason a flat-burr grinder is often “purged” before a shot.
What comes out
This is where it becomes something you taste.
Conical burrs produce a wider spread of particle sizes. Not because they are imprecise, but because of the geometry: coffee takes multiple paths through the narrowing gap, and different paths give different results. The distribution has a main peak plus a noticeable population of finer particles.
Flat burrs produce a narrower spread. Coffee takes essentially one path between two parallel surfaces, so particles come out more alike.
In the cup, the general tendency — and it is a tendency, not a rule — is:
Conical gives a rounder, heavier, sweeter cup with more body. The mix of particle sizes means several extraction rates happening at once, which produces a blended, forgiving result. Classic espresso character.
Flat gives a more separated, defined cup where individual flavours are easier to pick out. The uniform particles extract at similar rates, so the result is more transparent — which shows off a good coffee and equally shows up a mediocre one.
Which to choose
Follow it from what you actually drink.
Espresso with milk. Conical. Body and sweetness survive milk; delicate separated notes do not. This is why so many café grinders for milk drinks are conical.
Espresso, black, lighter roasts. Flat, if that is the direction you enjoy. Clarity is the point of a light roast, and flat burrs preserve it.
Filter and pour-over. Flat has a real advantage. Uniform particles matter more in filter brewing, where fines pass through and produce muddiness, and where the extraction is gentler and less forgiving of a wide distribution.
Both espresso and filter on one grinder. Conical is generally the easier compromise. Flat burrs optimised for espresso are often mediocre at filter grind sizes and vice versa; conical handles the range with less penalty.
You have not decided yet. Conical. It is more forgiving of dialling-in mistakes, which is most of what the first months are.
What burr size means
Larger burrs grind more consistently — more surface area doing the work, less heat per unit of coffee. But the returns diminish sharply, and past a certain point you are buying throughput speed, which matters in a café and does not matter for two cups a morning.
The specification is worth comparing between similar grinders and is not worth paying a large premium for at home.
What burr material means
Steel is the default. Sharp, effective, wears slowly, sharpens predictably. Fine for anything.
Ceramic stays sharp longer and generates less heat, but is brittle — a stone in your beans can chip it, where steel would survive.
Coated steel (titanium nitride and similar) extends life at some cost. Real but marginal at home volumes.
Burr material is far less important than burr shape or grinder build quality. It is a specification that sells grinders more than it changes coffee.
What is not on this list
Motor wattage, hopper capacity, number of preset buttons, and whether the grinder is branded as an espresso grinder. These appear prominently on product pages and none of them predict what is in the cup.
The short version
Conical for body and sweetness, and for forgiveness while learning. Flat for clarity and separation, and for filter brewing.
If you drink milk-based espresso, conical is the straightforward answer. If you drink black filter coffee from light roasts, flat. Between those two, either works, and the build quality of the individual grinder will matter more than the shape of its burrs.