Should you size up when buying a women's coat?

In short:

1. In most cases, keep your usual size: basic women’s coat patterns build in 15.5 to 18.5 cm of chest ease, against roughly 5 to 8 cm for a jacket.
2. A chunky 5 mm sweater adds about 3 cm at most to your chest girth (2π times the thickness): a coat’s ease absorbs it.
3. One size up only adds 4 cm of chest girth up to size 104 of the EN 13402-3 standard, then 6 cm, but it also widens the shoulders and lengthens the sleeves.
4. Size up if the coat’s chest girth is only about 10 cm above yours and you wear chunky knits, or if the shoulders feel tight; never on an oversized style.

When it comes to women’s coat size, the short answer is no: your usual size almost always works, even with a thick sweater underneath. A coat is cut looser than the rest of your wardrobe, and that room is already calculated to take layers. There are exceptions. They show up in centimetres, on three garment measurements: chest girth, shoulder width and sleeve length.

Women’s coat size: the measurements to check, in one table

Before ordering, these five benchmarks are enough to tell whether sizing up is worth it. They are orders of magnitude: the brand’s size guide has the final word for each model.

The last row explains why sizing up often disappoints. It adds 4 cm around, or 2 cm flat, which barely changes the room for a sweater. The shoulders, on the other hand, get wider and the sleeves get longer with it.

Should you size up for a coat?

The reflex starts from a sound idea: a coat goes over other clothes. Except that pattern makers have already allowed for it. Ease is the gap between the body’s chest girth and the garment’s. The basic women’s coat patterns published by the German pattern publisher M. Müller & Sohn, graded from 36 to 50, build in 18.5 cm of chest ease for a loose-fitting coat and 15.5 cm for a two-panel coat.

For comparison, a study published in 2019 in Fashion and Textiles measured the ease that 62 customers found comfortable in men’s suit jackets. The result: 5.17 to 8.25 cm at the chest depending on body size (Kim, Nam and Han, 2019). A classic coat therefore has two to three times as much room as a jacket at chest level.

The maths: how much room a sweater takes under a coat

A layer of thickness t wrapped around the torso adds 2π × t to the girth, roughly 6.3 times its thickness. A 2 mm fine knit adds 1.3 cm to your chest girth. A 5 mm chunky sweater, 3.1 cm. These are upper bounds, because the knit compresses under the coat.

Take the coat with 15.5 cm of ease. With the chunky sweater, just over 12 cm of room is left, more than the ease of a jacket worn over a shirt. For an 88 cm bust, the coat should therefore measure 103.5 to 106.5 cm around, or about 52 to 53 cm flat. A coat with those figures goes over a thick sweater without sizing up.

Sweater thickness depends mostly on the knit gauge and the yarn weight. As for the fibre, our cashmere vs merino comparison shows that cashmere makes a lighter sweater for similar warmth: under a fitted coat, that saves real room.

When sizing up makes sense

Four situations tip the balance towards the larger size.

• Your bust measurement sits at the top of your size range. The EN 13402-3 standard splits sizes into 4 cm intervals: size 88 covers 86 to 90 cm. At 90 cm, you are on the border of size 92.
• The shoulders feel tight. This is the hardest measurement to fix afterwards. If you wear a structured jacket under the coat, its shoulders have to fit inside: our guide to women’s blazer fits covers the different shoulder lines.
• The coat’s chest girth is only about 10 cm above yours, and you plan to wear chunky knits.
• The brand’s guide says the model runs small.

Conversely, sizing up does not fix a coat that is too short, or sleeves that alone are too short: it makes everything bigger at once. On an oversized coat, it is almost always a mistake.

Fitted, straight or oversized coat: the cut changes the answer

The same size does not give the same room from one cut to the next. The cut is the first thing to read on the product page, before the number.

A fitted coat follows the silhouette, with a waist shaped by seams or a belt. This is the cut that leaves the smallest margin at the chest. If you wear chunky knits in winter, measure the garment flat before choosing: this is where sizing up is most likely to help.

A straight coat falls from the shoulders without marking the waist. With ease close to the 18.5 cm of the loose basic pattern, it takes a thick sweater in your usual size.

An oversized fit adds volume to the pattern itself and drops the shoulder seam onto the upper arm. Sizing up pushes that seam even lower and lengthens the sleeves over your hands. Between two sizes, take the smaller one. The reasoning is the same as for choosing an oversized shirt size.

Three special cases:

• Trench coat: it is mostly worn in spring and autumn, over thin layers. Your usual size almost always works.
• Puffer and parka: the padding takes up part of the inner volume. A chest girth measured on the outside overstates the real room inside.
• Thick wool cloth: same logic. A coat in boiled wool or thick melton is measured on the outside, and its inside is slightly narrower than its flat measurement.

How to take your measurements for a coat

For a women’s coat, the European size designation standard uses bust girth as the primary dimension and height as the secondary one (EN 13402, part 2). Part 1 of the standard defines how to take each measurement; the international standard ISO 8559-1 describes the same anthropometric measurements.

Grab a soft tape measure and, if possible, a second person.

1. Bust girth: standing, breathing normally, tape level under the armpits and across the fullest part of the bust, over the bra you will wear.
2. Hip girth: at the fullest part of the buttocks. It matters for a long straight coat, which has to close without pulling at the hips.
3. Back shoulder width: from one shoulder tip to the other, across the top of the back.
4. Arm length: the standard measures it from the tip of the shoulder to the prominent wrist bone, over the elbow, with the arm bent at a right angle and the fist on the hip.
5. Upper arm girth: at the fullest part of the upper arm. On a narrow sleeve, this is what jams with a sweater. For a jacket, the 2019 study quoted above puts preferred upper arm ease between 1.58 and 5.86 cm.
6. Height: barefoot, back against a wall.

Write everything down in centimetres. Then take the most useful measurement of all: lay a coat that fits you well flat, and note its chest girth, shoulder width, sleeve length and back length. Those figures beat any chart.

Reading the size guide: body or garment measurements

A coat size guide gives one of two kinds of figures, and mixing them up skews everything.

Body measurements tell you which figure the size is designed for: bust, waist and hip girth in centimetres. The ease is already in the pattern. If your bust falls within the range, that is your size, sweater included.

Garment measurements, often called flat measurements, describe the coat itself. A flat chest width of 54 cm gives a girth of 108 cm. Subtract your bust: what is left is the real ease, to compare with the benchmarks in the table at the top of this article.

Size numbers vary from one country and one brand to the next. European sizes, UK sizes, letters from XS to XXL, even T1, T2, T3 and T4 numbering at some brands: to switch from one system to another, use our women’s size conversion chart, then come back to the model’s centimetres.

In plus sizes, the gap between two sizes grows: above a 104 cm bust, the EN 13402-3 standard moves in 6 cm steps. One size up therefore changes the line of the coat more.

Sleeve length and overall length by cut

Sleeve length is judged with your arms by your sides. Tailoring practice has a coat sleeve cover the jacket cuff and stop where it starts to creep onto the back of the hand, which also leaves room for gloves. Compare the model’s sleeve length with your arm length. On a dropped shoulder or a raglan sleeve, the shoulder seam is no longer at the edge of the shoulder: measure instead from the centre back, at the base of the neck, to the wrist, on the coat as on yourself.

Sleeves that are too long can be shortened by a tailor, more easily when they have no working buttonholes. The shoulders, though, involve how the sleeve is set and the lining. Hence the order of priority: shoulders first, sleeves second.

Overall length depends on the cut. A pea coat or short coat stops at the hips, a three-quarter coat at mid-thigh. The classic topcoat ends at or just above the knee, while the overcoat proper extends below the knee, according to the encyclopedia entry on the overcoat. To see where the hem will fall, have your back measured from the prominent vertebra at the base of the neck to the point you want, and compare with the model’s back length.

Height comes into play here, not in the size number. The EN 13402 standard recommends reference heights in 8 cm steps: 160, 168 and 176 cm. Many product pages also give the model’s height and the size worn. At 1.60 m, one size up lengthens sleeves and a hemline designed for a taller figure even further: keep your size, and see whether the brand offers a petite line.

Between two sizes: how to decide

Five steps, in this order, settle most doubts.

1. Take your measurements: bust girth, shoulder width, arm length, height, and the flat measurements of a coat that fits you.
2. Read the cut of the model: fitted, straight or oversized.
3. Work out the ease of the smaller of the two sizes: the coat’s chest girth minus yours. About ten centimetres is enough for a chunky sweater; 15 cm and more is a comfortable classic cut.
4. Check the shoulders: the shoulder seam should sit at the edge of the shoulder on a fitted or straight cut.
5. Decide: the smaller size if ease and shoulders work, the larger one if not. On an oversized style, the smaller one.

One last check when the parcel arrives: coat closed, sweater on, cross your arms in front of you. If the back does not pull between the shoulder blades, the size is right.