Diapers falls in Class 5, pharma & supplements, and depending on what exactly you sell it can also fall in Class 16 or Class 24 or Class 3. 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 diapers returns 66 accepted descriptions, and most of them sit in Class 5. 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.
Medicines, vitamins, supplements, or other health and medical products.
35 accepted descriptions in the manual mention diapers. For example:
Paper products, printed materials, books, or office and art supplies.
6 accepted descriptions in the manual mention diapers. For example:
Fabrics, bedding, towels, or other textile home goods.
4 accepted descriptions in the manual mention diapers. For example:
Cosmetics, skincare, hair care, perfume, or non-medicated cleaning products.
4 accepted descriptions in the manual mention diapers. For example:
Diapers 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 diapers is Class 5; a shop or online store that sells it is retail store services (Class 35), and a business that does both files in both.
Pharmaceutical preparations, supplements and medicated goods. Two lines run through it. Medicated skin care is here while non-medicated skin care is Class 3. And the drug is here while the instrument is Class 10: adhesive bandages are Class 5, but syringes and orthopedic bandages are Class 10.
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 diapers Searches the live USPTO register, including sound-alike and meaning-alike names. First search $2, then $5.Diapers sits in Class 5, pharma & supplements. That is where the USPTO's own ID Manual puts it: 35 accepted descriptions mentioning diapers fall in Class 5. Depending on exactly what you sell it can also fall in Class 16 or Class 24 or Class 3.
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.