What the site is for
A recipe from another country names a flour that your shop does not sell. The type numbers look comparable — German Type 550, French T55, Czech T530, Italian tipo 0 — but they are set by different national standards that measure different things, so the numbers cannot simply be read across. This tool takes the flour a recipe calls for and names the designation you can actually buy where you are, with the figures side by side and a note on what changes in the bake.
How a mill makes flour
A modern mill is not a pair of grinding stones. A roller mill (German Walzenstuhl) passes the grain between pairs of fluted rollers turning at different speeds, which crack it open rather than crush it. The fragments then travel through sifters — stacked, shaking sieves, called plansifters — which sort them by size, and the coarser fractions go back through further roller passes. A mill is therefore a long loop of breaking and sorting, and the miller decides which of the resulting streams are recombined into a finished flour.
Two independent decisions come out of that loop, and they are the reason flour classification is confusing.
The first decision: how much of the outer grain goes in
A grain of wheat is, roughly, three things. The endosperm is the bulk of it: a starch store, with the gluten-forming proteins in it. The bran is the layered outer skin. The germ is the embryo, oily and small.
Almost all of the grain's minerals sit in the bran and the outermost layer of the endosperm; the starchy centre has very few. So the proportion of outer layers a miller lets into the flour decides its mineral content. That proportion is called the extraction rate (German Ausmahlungsgrad): a low extraction means little of the outer grain is present, and the flour is pale; a high extraction means much of it is, and the flour is dark. At 100 % extraction nothing has been removed and the product is wholemeal.
Extraction is a process figure and cannot be measured in a finished bag. What can be measured is what it leaves behind. Burn a weighed sample of flour at high temperature: the organic matter — starch, protein, fat — goes off as gas, and the minerals remain as a grey residue. Weigh that residue and you have the ash content, given as a percentage of dry matter. Ash is a stand-in for extraction, and it is the figure nearly every national standard is built on. German, Czech and Polish type numbers are simply the ash content in milligrams per 100 g of dry matter: Type 550 means about 0.55 % ash.
The second decision: how finely it is ground
While sorting the fragments, the mill also decides how large the particles in the finished product are. This is the grind or particle size, and it is independent of extraction: two flours can have exactly the same ash content and quite different particle sizes, because one was taken from a finer sifter stream than the other.
Particle size matters because it governs how fast the flour takes up water. Fine flour hydrates quickly; coarse flour hydrates slowly, so a dough made with it feels correct at the mixer and then tightens over the following twenty minutes as the water works in. Fine milling also damages more of the starch granules, and damaged starch absorbs several times its own weight in water, which shifts the whole hydration of a recipe.
Countries part company here. Austria, Czechia and Hungary treat particle size as part of the flour classification itself, with legally defined sieve bands — Austrian glatt and griffig, Czech hladká, polohrubá and hrubá. Most other countries do not: their coarser products leave the flour category altogether and become a separate article of trade, such as German Dunst and Grieß, Italian semola, French semoule, Polish kasza manna or American farina. This is why a German cannot easily buy the Czech semi-coarse polohrubá: the German system has no semi-coarse flour to sell.
What the mill cannot change: protein
Protein content and protein quality come from the field, not the mill. They depend on the wheat variety, the soil, the weather and above all the nitrogen the crop was given. A mill can blend lots to hold a consistent figure, but it cannot raise the protein of the grain it receives.
Protein matters because of gluten. When wheat flour is wetted and worked, two protein groups combine into an elastic network — the gluten network (German Klebergerüst) — that traps the carbon dioxide from fermentation and lets a dough rise. More protein generally means a stronger network, more water absorbed, longer mixing, better gas retention and more oven spring (the sudden expansion in the first minutes of baking), and a chewier crumb (the open interior of the loaf). Less protein means a tender, short result, which is what a cake or a shortcrust wants and a bread does not.
Rye is a different case. It contains proteins but they do not form a gluten network; rye dough is held together by pentosans and by acidity, which is why rye bread is a sourdough matter and a pure rye dough will not behave like a wheat one. Durum wheat is a different species again, harder in the endosperm and higher in protein, milled into coarse semolina for pasta rather than into bread flour.
Total protein is measured as nitrogen times 5.7. But two flours at the same protein figure can behave very differently, because the composition of the protein differs. So laboratories also measure gluten quality directly, by deforming a dough and recording the force. The alveograph inflates a disc of dough into a bubble until it bursts and reports the energy needed as the W value; the farinograph records the resistance of a dough during mixing at constant consistency. Roughly, biscuit flour sits at W 90–130, bread flour at W 250–300 and long-fermented pizza flour at W 300–350. Two flours both at 12.5 % protein can sit at W 180 and W 320, which is a large practical difference. The two instruments measure different things and their readings cannot be converted into each other. Neither figure usually reaches a retail bag, which is why this site does not treat it as an axis.
What the standards actually fix
Each country regulates a different subset, and that is the heart of the problem.
Germany fixes ash and nothing else. Italy fixes ash and a minimum protein. Austria fixes ash, particle size and acidity. Hungary fixes ash, wet gluten, particle size and dough rheology. Switzerland fixes ash and, for wholemeal, the extraction rate. The United Kingdom fixes nothing about composition at all — its regulations cover only fortification, the calcium, iron and vitamins that must be added. The United States sets no ash band either, but caps ash against protein by a formula, and separates flour, farina and semolina into distinct standards of identity.
Where a standard fixes a figure, this site shows it as regulated. Where it does not, the range shown is ordinary market practice, gathered from what mills actually sell, and is marked as such. That distinction is the difference between a legal limit and a habit, and it is worth reading before trusting a number.
Reading a substitution
Two flours are close when their ash and protein ranges overlap and their grind matches. A different grind is not a small matter: it changes hydration and handling regardless of the numbers, so this site never calls a swap across grinds a close match. A different grain — rye for wheat, durum for common wheat — is not a substitution at all.
Where the figures differ, the practical corrections are consistent. More protein: add water, mix longer, expect more spring and more chew. Less protein: take water out, mix briefly, handle gently, expect a flatter and more tender result. More ash: slightly more water, but the bran particles cut through the gluten network, so mix gently, shorten the bulk fermentation and expect a darker, denser crumb. Less ash: slower fermentation and a milder flavour, so allow more time. Coarser grind: rest the dough before judging the water. Finer grind: add water in stages and stop mixing sooner.