The short answer on Green Hat: pick one anchor piece, keep the palette to two colours, and let the shoes decide how formal the whole thing reads. One piece should lead and the rest should stay quiet; two competing pieces read as an accident. Proportion does more than colour: volume on top wants something narrow below, and the reverse. Hat sizing is a circumference in centimetres. Measure once and you never guess again. The groups below run from the decision that matters most to the ones you make afterwards.

What decides this is crown depth, brim width and circumference. Everything else is preference. Two from the first group show the range: Casablanca's Green Striped Crochet Hat at $180, and Casablanca's White & Brown Stripe Crochet Hat at $180. The first is the easy entry point; the second is where the money goes. Hat sizing is a circumference in centimetres. Measure once and you never guess again. A higher price mostly buys materials and finishing, and occasionally it buys nothing at all.

A hat commits the whole outfit. Keep the rest simple. From the second group, aninebing.com's Jeremy Baseball Cap Ab Los Angeles - Sea Foam Green ($70) is the one that earns its place, because it works in more than one context without being restyled. The third group is smaller and deliberately narrower, hats, for the decisions you make after the main one. None of this needs the whole group. One piece from each is usually enough.

There are 20 hats here from 11 brands, $35 to $450, all in stock when this was written. We would not buy all of them, and neither should you. Norma Kamali's LONG BILL BASEBALL CAP at $35 is the low-risk way in, and La Garçonne's Wald Hat - Green Spruce at $450 only makes sense if this is a category you already use constantly. On green hat specifically: the difference between the top and the bottom of this list is real but smaller than the price gap suggests. Nothing here is included because it is famous, and price is not used as a proxy for quality anywhere on this page. If you take one thing away: buy the one you can picture using this week, not the one you are saving for later.