What to Wear in 40 Degree Weather (4°C)

In 40 degree weather, about 4 degrees Celsius, wear a proper coat. A wool overcoat or a light puffer over a knit, full-length trousers, closed boots, and something at the neck. Forty is the temperature where layering stops being enough on its own and outerwear becomes the outfit, so the question is no longer what you wear but what goes over it.

Forty is the coat threshold

Below about ten degrees Celsius, a jacket stops being optional and starts being the thing everybody sees. At 40°F you will be photographed, greeted and remembered in your coat, not in what is underneath it. That changes the order you should get dressed in.

Pick the coat first, then build underneath it. Two consequences follow:

• The coat has to fit over a knit. A wool coat that only closes over a t-shirt is a 50-degree coat.

• The proportions are the coat's proportions. A long coat over a midi skirt works. A long coat over a mid-thigh dress usually does not, because the hem disappears and the outfit reads as coat with legs.

The four-piece formula

1. A long-sleeve base. A fine knit, a polo neck, a thin merino layer. Not cotton if you will be outside for more than twenty minutes, because it holds damp.

2. A mid layer you can remove. A jumper, a cardigan, an overshirt. This is the piece that makes the indoors survivable.

3. A coat that closes. Wool overcoat, light puffer, quilted jacket, parka.

4. One warm accessory. A scarf does more at this temperature than a whole extra layer, because most heat leaves through the neck.

Gloves are not required at 40 unless it is windy. A hat is not required unless it is wet. The scarf is required.

Five outfits for 40 degree weather

1. Wool overcoat, polo neck, straight jeans, ankle boots

The default. Works for the office, works for a weekend, works in every city.

2. Long coat, knit midi dress, opaque tights, knee-high boots

The dressed-up version. Opaque tights are worth 5 degrees on their own, and knee-high boots close the gap the coat leaves.

3. Light puffer, jumper, wide-leg trousers, chunky boots

The warmest and the most casual. A short puffer over wide-leg trousers keeps the proportions from going square.

4. Trench coat with a liner, fine knit, dark jeans, loafers

The mild-and-dry version of 40, and the one that fails the moment there is wind. Trench coat outfits covers what goes under it.

5. Quilted jacket, cardigan, cords, flat boots

The school run and the dog walk. Cords are warmer than denim and nobody mentions it.

The awkward part of 40-degree dressing is that you own four coats and rarely remember what is under each of them. If your outerwear is photographed into Wdrobe, you can build the whole thing including the coat before you open the wardrobe.

What 40 feels like, and when it lies

Forty degrees in still sunshine feels like 50. Forty degrees with a 20mph wind feels like 30. Rain drops the effective temperature further than most people expect, because a wet wool coat stops insulating.

Three checks before you leave:

• Wind speed, not just temperature. Above about 15mph, swap the wool coat for something windproof.

• What time you come home. Four o'clock and eight o'clock are different temperatures. Dress for the later one.

• How long you are actually outside. Ten minutes to a car is a different outfit from forty minutes on a platform.

The indoor problem

Most buildings at this time of year are warmer than you want. The mid layer exists to be taken off, so it needs to be a garment you are happy to be seen without: a cardigan over a knit, not a jumper over a vest.

This is the single most common 40-degree mistake. People dress for the walk, arrive, and then sit in a meeting in a thick jumper for three hours.

Frequently asked questions

What should you wear in 40 degree weather?

A wool coat or light puffer over a long-sleeve knit, full-length trousers, closed boots and a scarf. Add a removable mid layer such as a cardigan so you are not stuck in your outdoor clothes once you are inside.

What should ladies wear in 40 degree weather?

A knit midi dress with opaque tights and knee-high boots under a long coat, or a polo neck with straight jeans and ankle boots. Opaque tights make a dress viable at this temperature in a way bare legs are not.

Is 40 degrees cold enough for a winter coat?

For a light one, yes. A wool overcoat or a light puffer is right at 40°F, or 4°C. A heavy down parka is usually too much until the temperature drops closer to freezing.

Do you need a hat and gloves at 40 degrees?

A scarf, almost always. Gloves only if it is windy or you will be outside for more than half an hour. A hat mainly for rain, since a wet head is what makes this temperature feel much colder than it is.

If the forecast is milder than you thought, what to wear in 60 degree weather is the right guide, and for the layering method underneath any coat see winter layering outfits.

You know the formula now. What you cannot see from the forecast is whether the coat you plan to wear actually closes over the jumper you plan to wear under it, which is how most people end up leaving the house cold. Wdrobe lets you build the outfit including the coat, on screen, the night before. Stop guessing at the door.