Flour falls in Class 30, coffee, snacks & baked goods, and depending on what exactly you sell it can also fall in Class 1 or Class 7 or Class 29. Everything below is read from the USPTO's own list of accepted descriptions, not from an opinion about where it belongs.
Searching the USPTO Trademark ID Manual for flour returns 83 accepted descriptions, and most of them sit in Class 30. The manual is the list of identifications the office has already approved, so wording taken from it is pre-approved and settles the class at the same time.
The class follows from the identification you write, so "what class am I in" is really "what exactly do you sell". How the class system works covers the rest.
Coffee, tea, bread, sweets, snacks, or pantry staples like flour, spices, and sauces.
65 accepted descriptions in the manual mention flour. For example:
Raw chemicals, adhesives, or additives used in industry, science, farming, or manufacturing.
8 accepted descriptions in the manual mention flour. For example:
Machines, power tools, motors, or engines (other than for land vehicles).
4 accepted descriptions in the manual mention flour. For example:
Meat, dairy, eggs, snacks, or other prepared and preserved foods.
3 accepted descriptions in the manual mention flour. For example:
Flour appears in 4 classes because what you make, what it is made of and the service of selling it are separate classes. Pick the descriptions above that match what you actually do.
Making flour is Class 30; a shop or online store that sells it is retail store services (Class 35), and a business that does both files in both.
Coffee, bread, snacks and pantry staples. Dairy and oils sit next door: cheese and edible oils are both Class 29.
The class decides what a registration covers; it does not decide whether the name is available. Relatedness is judged on the identifications, so a conflict can sit in a class you never looked at: the same name in a different industry.
Check whether your name is clear for flour Searches the live USPTO register, including sound-alike and meaning-alike names. First search $2, then $5.Flour sits in Class 30, coffee, snacks & baked goods. That is where the USPTO's own ID Manual puts it: 65 accepted descriptions mentioning flour fall in Class 30. Depending on exactly what you sell it can also fall in Class 1 or Class 7 or Class 29.
You file in every class you actually use the mark in, and the USPTO charges its fee per class. Selling a product and also running an online store for it is two classes, not one. Filing in classes you do not use is worse than filing in too few: an application has to be supported by real use or a genuine intent to use.
No. The class decides what a registration covers. Availability turns on whether someone already holds a similar mark for related goods, and relatedness is judged on what the identifications say rather than on the class number, so marks in different classes can still conflict.
Not what you sell? Search the class finder for your own wording, or browse all 45 classes.