Guide one
A brim is a seating problem.
Before it is a question of style, brim width is a question of how much room there is between you and the person next to you. Almost everyone finds that out on the day.

A 13 cm brim will bump the person next to you in a church pew.
Church pews and banqueting chairs sit roughly 45 to 50 cm apart, centre to centre. A 13 cm brim adds 26 cm to the width of your head. The arithmetic does the rest.
Under 10 cm sits better indoors. That is not a rule anyone made; it is what is left once you subtract the furniture.
No brim
Pillbox, cocktail, fascinator, headband, comb
Nothing projects past the outline of your head. Works in every seating arrangement, every doorway and every car. If you have never worn occasion headwear before and the event is indoors, start here.
Up to 10 cm
A-01, E-04 at 12 cm is already past this
Generally clears a seating row. Reads as a hat in a photograph taken from three metres. The width that survives an indoor ceremony followed by an outdoor reception without becoming a problem in either.
12 to 14 cm
A-02, A-05, A-06, A-07, E-04
Outdoor width. In a pew or a banqueting row it overlaps the person beside you. Outdoors it holds its own at distance, which is what most people are picturing when they picture a wedding hat.
16 cm and over
A-04, A-08
A decision about the whole day. Needs an outdoor ceremony, a car you can sit upright in, four anchor points, and somewhere for it to go during the meal. Where those are not all true, a narrower brim is not a compromise — it is the correct answer.
Four things width changes
Wind
Every extra centimetre is leverage. At 13 cm you need four anchor points; at 18 cm, four and a plan.
Photographs
A wide brim casts a hard shadow across the face in direct overhead sun. Outdoors at noon, an upturned or asymmetric brim keeps the face open.
Doorways and cars
Anything over 14 cm has to be carried through a car door, not worn through it.
The person beside you
Indoors this is the whole calculation. Outdoors, standing, it stops mattering almost entirely.
Every brim in the range, by width
- 10A-01 — Brim Sinamay 10 cm118 g · rigid box required$148
- 12A-03 — Brim Upturned136 g · rigid box required$198
- 12A-05 — Brim Satin Trim158 g · rigid box required$248
- 12E-04 — Brim Veiled168 g · rigid box required$328
- 13A-02 — Brim Sinamay 13 cm142 g · rigid box required$178
- 13A-06 — Brim Feathered176 g · rigid box required$328
- 13F-04 — Wedding Guest Set946 g · rigid box required$248
- 13F-05 — Races Set980 g · rigid box required$388
- 14A-07 — Brim Draped172 g · rigid box required$368
- 16A-04 — Brim Asymmetric165 g · rigid box required$228
- 18A-08 — Brim Couture214 g · rigid box required$498
- 18F-06 — Couture Set1010 g · rigid box required$598