Flour type numbers, and the three things they measure

A German bag says 550, a French one T55, a Japanese one 薄力粉 and an American one says all-purpose. Those four labels are not four names for the same scale. Two of them grade mineral ash, one grades protein and one is a category name, which is why every mapping between them is an approximation rather than a translation.

Ash: the German and French numbers

Burn a hundred grams of flour and weigh what will not burn. The mineral residue, mostly from the bran, is the ash content, and the German and French numbers report it. More bran means a higher number, a darker flour and a stronger flavour.

The number on the bag names a band. DIN 10355 gives each German type a floor and a ceiling, so a sack stamped 550 has to land between 0.51 and 0.63 percent ash, and two sacks carrying that same number on the front can sit 120 milligrams apart with both labels correct. Hessen's consumer authority, citing that standard, gives the reason the figure moves at all, which is that the grain itself varies from harvest to harvest.

Read the two ash columns across and the ladders slip past each other. A French miller puts T80 at 0.75 to 0.90 percent and labels the column a repere, a reference point; the German 1050 band opens at 0.91, where T80 has already closed. The pairs on each row bake alike, which is why they sit together, and that is a softer claim than sharing an ash figure. Where a French and a German number do overlap, as 550 and T55 do across most of their range, the swap is closer to safe.

That last column is the one to hold loosely. Ash measures how much of the grain is in the bag. The American names measure protein, which decides how much gluten develops. The two are related, since bran comes with protein, but they do not track each other, which is why you can find guidance saying T55 is American all-purpose and, a paragraph later, that all-purpose has less ash than T55 and needs whole wheat added. Both statements are defensible on their own axis. Neither is a conversion.

Protein: the Japanese system

Japan grades the other property directly, by protein percentage, and names each band.

American all-purpose sits at about 10-12 percent, which lands between chuurikiko and junkyourikiko and matches neither. There is no Japanese bag equivalent to all-purpose, and that gap has a named consequence: a Japanese sponge recipe calling for hakurikiko made with all-purpose comes out tough, because the recipe assumes a flour two bands weaker than the one in your hand.

Italy numbers the same property a different way

An Italian bag says 00, 0, 1, 2 or integrale, and the ladder runs the same direction as the German and French one: 00 is the most refined and integrale is wholemeal. The difference is what the label is. A German 550 and a French T55 print the ash figure itself, so the number on the bag is the measurement. Italian grades are classes, each with an ash range set in law, and the label names the class rather than the reading. So 00 tells you which bracket the flour falls in, not how much bran is in it, and two 00 flours from different mills can sit at different points inside the same bracket. That is why Italian recipes so often name the mill as well as the grade, and why 00 alone is a weaker instruction than T55 alone, even though both are the everyday refined flour of their country.

Pizza flour muddies it further. Much of what is sold abroad as 00 pizza flour is a strong bread flour that happens to be milled to the 00 class, so it carries the refinement of a cake flour and the protein of a bread flour at once. The class and the strength are independent, which is the same lesson as the ash-versus-protein split above, arriving from a third direction. The 00 grade in a whole Italian recipe, next to the etto and quanto basta, is on Italian recipe measurements.

The number tells you how it bakes, not what it weighs

This is the part that matters on a conversion site. The Japanese standard tables weigh every flour type at roughly the same amount per cup, even though the protein runs from 6.5-9 to 11.5-13 percent across the range. Bulk density barely moves; what moves is the gluten the flour will form once it meets water. So a type number is not a conversion factor, and swapping 550 for 405 in a recipe changes the crumb without changing the grams. The weight of a cup of flour, and the argument between the authorities who measured it, belongs on our flour master, which publishes 120 g and names the source.

What the bag prints, and what it still cannot settle

A supermarket bag in the EU does print protein. Regulation 1169/2011 made the nutrition declaration mandatory and protein is one of its required lines, so a sack of Francine T45 states 8.4 g of proteines per 100 g and a bag of Belbake Type 1050 states 12 g of Eiweiss. What that line will not do is settle a substitution. It is a nutrition figure for the food, averaged for the label, and an American bag carries the same line under its own labelling rule, printed per serving instead. The number stamped beside it on a European bag grades ash, a different property altogether. So a baker holding the bag can read both figures and still not know whether this flour behaves like the one the recipe assumed. That is why these mappings stay approximate: the milling specification that would settle it never reaches the shelf.

What to buy, in practice

For a French or German recipe, match the rung rather than the number: 550 and T55 behave like all-purpose, 405 and T45 like cake flour, 812 and T65 like bread flour. For a Japanese recipe, the substitution runs the other way and needs help: all-purpose is stronger than hakurikiko, so cake flour is the closer buy for anything Japanese that wants a tender crumb. Where a recipe depends on the difference, buying the named flour beats approximating it, and where it does not, the rung is enough. Polish typ numbers grade the same property on the same scale, so typ 550 is all-purpose, though the ladders do not match rung for rung: Polish cake flour is typ 450 against the German 405, decoded for a whole recipe on Polish recipe measurements.

Questions about flour types

What is T55 flour in American terms?

All-purpose, near enough to bake with. The caveat is that T55 is graded by ash and US all-purpose by protein, so the two labels are describing different properties that happen to overlap on this rung of the ladder.

Can I use all-purpose for a Type 405 cake recipe?

You can, and expect a firmer crumb. US all-purpose already carries protein at about the level of Type 550, so substituting it into a 405 recipe moves you one rung up the ladder rather than sideways.

Does the type number change how much a cup weighs?

Barely. The Japanese tables weigh every flour type at about the same figure per cup despite protein running from 6.5-9 to 11.5-13 percent. The number on the bag changes how the flour behaves, not what it weighs, so our gram tables stay on the flour page.

Sources

Brot und Meer for the German ash-type mapping to US flours, French milling references for the T-scale, and the Japanese Food Composition Tables for the protein bands and the per-cup weights that barely move across them. Full citations on the sources page.