Oversized shirt: should you take your usual size or one size down?

In short:

1. An oversized shirt is big by design: on two men’s shirts in size M consulted on 20 October 2026, the flat chest width goes from 59.7 cm (relaxed fit) to 66 cm (lightly oversized fit).
2. Take your usual size if the fit is sold as oversized; go one size down if the ease (twice the flat width, minus your chest girth) is more than you want.
3. One size apart changes the garment’s chest girth by 2.5 to 6.4 cm, but the back length by only 0 to 2.5 cm: sizing down removes width, not length.
4. For the same letter, a men’s shirt targets about 4 cm more chest girth than a women’s shirt (men’s M: 94 to 102 cm; women’s M: 90 to 98 cm, under the EN 13402 standard).

With an oversized shirt, what size to get depends first on how it was cut. If the product page says oversized fit, the volume is already built into the pattern: your usual size is enough, and a size up quickly turns into the pyjama look. If you want a more measured volume, one size down works, provided the sleeves and length still fit. The real judge is the garment’s size guide read in centimetres and set against your own measurements.

The measurements that decide the size of an oversized shirt

One thing stands out: the oversized shirt in this example does not have the widest shoulders. It gains 6.3 cm of flat chest width but loses 1.3 cm across the shoulders. The volume of a roomy cut does not always sit where you expect it, which is why a single measurement is never enough to choose.

What makes an oversized fit, measurement by measurement

A shirt becomes oversized through its ease, the gap between the garment’s girth and the body’s girth. Pattern-making manuals separate wearing ease, the room needed to sit and move, from design ease, added by the designer to create a silhouette. According to the encyclopaedia entry on ease, wearing ease at the bust sits around 5 to 6.4 cm depending on the author. Anything beyond that is style.

Chest ease, in centimetres

A study published in 2021 in the International Journal of Clothing Science and Technology varied the ease of women’s shirts on an adjustable dress form: for the fitted shirt, the ease judged suitable from the front ranged from 1 to 7 cm at the bust, and about 4 cm at every point for the straight shirt (Sakata, Kim and Takatera, 2021).

Set against those figures, the two shirts in the table are on another scale. For a man in size M, with a chest girth of 94 to 102 cm under the EN 13402 standard, the relaxed fit leaves 17 to 25 cm of ease and the lightly oversized fit 30 to 38 cm. As an order of magnitude, three levels stand out:

• Fitted: about 1 to 7 cm of ease.
• Relaxed or loose: around 15 to 25 cm.
• Oversized: 30 cm and more.

These levels are benchmarks drawn from a few published examples, not thresholds set by a standard. They help you place a shirt before buying it.

Dropped shoulders

On a classic shirt, the shoulder seam sits on the shoulder bone and the sleeve is set into the armhole. A dropped shoulder moves that seam lower, onto the upper arm: the sleeve starts further from the neck, and the armhole is wider. It is the detail that gives an oversized fit its relaxed look, even when the flat width stays reasonable.

In practice, on a dropped shoulder, the shoulder width in the chart will naturally exceed yours, and that is intended. Do not size down for that reason alone. Look instead at whether the seam falls a few centimetres below your shoulder, as on the product photo, or all the way to the elbow, which signals a very roomy model.

Sleeve length and overall length

Sleeve length is hard to read on a dropped shoulder, since the sleeve starts lower. The dependable measurement runs from the centre back of the collar to the wrist: it adds half the shoulder to the sleeve and stays comparable from one cut to another. On the two shirts in the table, it ranges from 78.7 to 80 cm in size M.

Overall length decides how you wear the shirt: tucked in, knotted, open as an overshirt or worn over trousers. Both examples measure about 78 cm at the back. Take the same measurement on yourself, from the base of the neck to where the hem should fall, and compare.

How to compare the garment chart with your measurements

A size guide can give two very different things: the body measurements a size is meant for, or the measurements of the garment itself. For an oversized shirt, the second set is what counts, because the first says nothing about the added volume.

1. Measure your chest girth with a tape measure, horizontally, under the arms. The method follows clothing size standards such as ISO 8559-1.
2. Find the flat chest width in the garment chart and double it. If the brand already gives a full girth, do not double it: check the column heading.
3. Work out the ease: subtract your chest girth from the garment girth. Place the result in the levels above.
4. Lay flat a shirt you like, buttoned, without stretching the fabric, and take the four measurements in the table. It is the safest benchmark, because it puts into centimetres a drape you already know.
5. Compare length and sleeve before choosing between two sizes.

If your measurements fall between two sizes, the chest decides for a shirt. To convert a UK or US size afterwards, our women’s size conversion chart gives the equivalents and the chest girths for each French size.

Usual size or one size down: how to decide

The answer depends on what the brand has already built in.

• The shirt is sold as an oversized fit: take your usual size. The volume is in the pattern, and a size up mostly adds width, not style.
• The product page says the model runs large: go one size down, it is the most direct information you have.
• Your calculation puts the shirt at the top of the oversized level and you want a clean volume rather than a blanket effect: one size down removes 2.5 to 6.4 cm of girth and brings the ease closer to the relaxed level.
• You want an oversized look from a classic shirt: then it is one or two sizes up, not down. On a straight cut, the starting ease is only a few centimetres.

Before sizing down, look at what you give up. On the three product pages consulted on 20 October 2026 (the two shirts in the table and an overshirt measured in centimetres), moving from one size to the next changes chest girth by 2.5 to 6.4 cm, back length by 0 to 2.5 cm and the sleeve measurement by 0 to 3.8 cm. One size down therefore mostly takes away width. For a tall person, the sleeve is what may end up too short; for a shorter person, the trade works in their favour.

The same reasoning applies to other roomy pieces. The different women’s blazer fits, straight, tailored or oversized, are also read through shoulder width and length, and our guide to choosing a women’s coat size covers the same question for a piece worn over other layers.

A men’s shirt worn by a woman

Borrowing from the men’s section is still the simplest way to get an oversized fit. The two sections do not measure the same things.

The European standard EN 13402 designates a men’s shirt size first by neck girth, then by height and arm length; a women’s blouse by bust girth, then by height (encyclopaedia entry on the EN 13402 standard). In its tables, a 39 cm collar corresponds to a 96 cm chest girth, a 40 cm collar to 100 cm, a 41 cm collar to 104 cm.

For letter sizes, the same standard proposes these ranges:

For the same letter, the men’s size targets about 4 cm more chest girth. A woman who wears an M can keep her letter in the men’s section for a roomy effect, or take an S for a shirt closer to her measurements. With collar sizes, a woman with a 90 cm bust finds her base between a 37 and a 38 cm collar (88 to 92 cm), and aims for a 40 or 41 cm collar for an oversized volume.

Then there is the sleeve. The standard links an arm length of 62 cm to a height of 164 cm and 66 cm to a height of 180 cm. A men’s shirt cut for a tall build reaches further down the wrist: that is what gives the rolled-up sleeves typical of this look. Plan two or three turns rather than an alteration.

One last detail: a men’s shirt is most often cut straight, without bust darts. For a fuller bust, the flat width must cover the bust girth with comfortable ease, or the buttons will gape.

Fabric, washing and silhouette: what changes the drape

Two shirts with the same measurements do not hang the same way. A tight cotton poplin keeps a crisp, almost structured shape; linen or viscose drape more and give a softer volume. Our article on viscose fabric explains what makes it fluid and how to care for it.

Shrinkage in the wash also matters when choosing between two sizes. A cotton or linen shirt that has not been pre-treated can lose a little length in the first wash: the care label and the composition give the clue. If you hesitate between two sizes in a fabric like this, the larger one leaves a margin.

For the silhouette, a roomy shirt is balanced by a closer-fitting bottom, straight jeans or a straight skirt, or on the contrary by a deliberate volume below, such as wide-leg or palazzo trousers with the shirt tucked in. Worn open over a T-shirt, it also works as an overshirt; in that case, measure the flat width with the layer underneath included.

One figure to keep in mind when ordering: 6 cm. That is roughly the gap in flat chest width between a relaxed shirt and an oversized shirt of the same size in our examples, a little over 12 cm in girth. If the shirt you have in mind already exceeds your favourite shirt by that much, your usual size is the right one.