Four shapes cover nearly everything the weather and the calendar can ask for. The rest is variation.
A coat is the garment people see most and think about least. It goes over everything, it is worn in the street rather than indoors, and for half the year it is the only part of an outfit anyone actually registers.
Four shapes cover almost every situation. Owning one good example of each is a more useful wardrobe than owning eight coats that all do the same job.
One: The Trench
Lightweight, usually cotton gabardine, double breasted, belted, with a collar that stands. It is a rain coat by origin and a smart one by reputation.
What it is for. Spring and fall, over almost anything. It is the only coat on this list that reads formal and casual equally well, which is why it survives.
What to look for. A collar with enough structure to stand when turned up. A belt that buckles rather than ties, or at least one with a buckle option. Length at or below the knee, because a cropped trench loses the line the coat is known for.
Worn open with the belt tied at the back is the version most people reach for, and it is the easiest.
Two: The Tailored Wool Coat
Single or double breasted, in wool or a wool blend, cut like a long jacket. The dress coat of the group.
What it is for. Cold weather where you need to look pulled together. Over a suit, over a blazer, over a dress, over anything that would be undermined by a puffer.
What to look for. Wool content above fifty percent, because anything less loses shape and pills. A shoulder that fits over a knit, which is the fit rule below. And a length that either stops above the knee or falls well below it, since mid knee is the least decisive place to end.
Three: The Casual Jacket
Utility, field, chore or bomber. Hip length, usually cotton or a technical cloth, with pockets that are meant to be used.
What it is for. Everyday, mild weather, and anything where a coat would be too much. The one that gets worn most and replaced most often.
What to look for. A hem that sits at the hip rather than above it, because a short jacket over a long layer looks accidental. A collar that fastens if you want it to.
Four: The Warm One
Puffer, parka or heavy shearling. Function first.
What it is for. Actual cold. There is no styling substitute for insulation, and a beautiful wool coat in January is a beautiful wool coat you are cold in.
What to look for. A hood if you will use it, and a length that covers the seat if you spend time outdoors. A longer puffer is considerably warmer than a short one and reads less sporty.
A beautiful wool coat in January is a beautiful wool coat you are cold in. There is no styling substitute for insulation.
The Fit Rule
A coat is sized over other clothes, and that is where most coat buying goes wrong. A coat tried on over a T-shirt in a warm store will not close over a knit in December.
Wear or carry the thickest thing you expect to layer underneath, and try the coat over it. Check three places.
The shoulder. On a tailored coat the seam sits on the edge of the shoulder with room for a sleeve beneath. If it is already at the edge over a shirt, it will be pulled past it over a sweater.
The armhole. Raise your arms. A coat with a tight armhole lifts the whole garment and is uncomfortable within minutes.
The button or zipper line. Fasten it and sit down. A coat that pulls at the closure when seated will not be worn fastened, which defeats the purpose.
Length, and What It Does to Everything Below
A coat hem creates a horizontal line, and it is the most visible one in an outfit because the coat is the outer layer.
Hip length. Casual, easy, and it keeps the leg long. Works over trousers, less well over a long dress where the dress hem appears a long way below.
Knee length. The most formal and the most neutral. Covers almost any dress or skirt.
Below the knee or full length. Dramatic and warm. Needs the hem of whatever is underneath to be shorter than the coat, or the layering reads muddled.
The one combination to watch is a coat ending within an inch or two of a skirt or dress hem. Either clearly longer or clearly shorter reads deliberate; almost the same reads like a mistake.
What Goes Underneath
A coat is the only garment designed around other garments, so it is worth thinking about the stack rather than the coat alone.
The useful principle is that bulk should decrease as you move outward in volume but increase in warmth. A fine base layer, a mid weight knit, then the coat. Two thick layers under a fitted coat is where the shoulder goes and the sleeves stop moving.
A vest is the exception worth knowing, because it adds core warmth with nothing at the arm, which is exactly what a fitted coat sleeve needs.
Color
A coat is worn more often than anything else in the wardrobe, so it should go with most of what is underneath. Camel, navy, charcoal, black and olive all qualify.
A colored coat is a pleasure and a commitment, since it will be the loudest thing in every outfit it appears in. Worth owning as a second coat, rarely as the only one.
Care
Brush a wool coat after wearing rather than cleaning it. Dry clean once or twice a season at most, since the process is harder on wool than most people realize. Hang it on a broad hanger that supports the shoulder, because a wire hanger will put a point in it that never comes out.
Coats and Jackets to Consider
Common Questions
Can You Wear a Coat Over a Blazer?
Yes, and it is a standard combination, but the coat has to be cut for it. A blazer adds structure at the shoulder and bulk through the body, so a coat sized over a shirt will pull. Look for a coat with a shoulder seam that sits slightly wider than you need and an armhole with room, then fasten it and sit down before deciding. The other consideration is length: the coat should be clearly longer than the blazer, by several inches at least, or the two hems compete. A knee length coat over a hip length blazer is the reliable version.
The Short Version
A trench for spring and fall, a tailored wool coat for cold weather that needs to look smart, a hip length casual jacket for ordinary days, and something genuinely insulated for real winter. Buy each one over the thickest layer it will cover, check the shoulder and the armhole, and decide the length so the hem is clearly longer or clearly shorter than what is underneath. Four coats, and the weather stops being a problem.