How to read a size chart when every brand means something different

There is no authority that defines what a medium is. No standards body, no legal definition, no industry agreement. Each brand decides for itself, based on who it thinks its customer is — and then drifts over the years as that idea changes.

This is why you can wear a medium in one shop and a large in the next without having changed shape. The letter is a marketing decision. The numbers under it are the actual garment.

Ignore the letter, read the measurements

Almost every size chart has a table of measurements behind it. That table is the useful part, and it comes in two very different flavours — which is where most of the confusion starts.

Body measurements describe the person the garment is intended for. "Chest 96–101cm" means if your chest measures that, this size is meant for you. The brand has already decided how much room to add.

Garment measurements describe the item flat on a table. "Chest 54cm" means the garment itself is 54cm across the chest, which is 108cm around.

The two are not interchangeable, and a chart that does not say which it is giving you is nearly useless. If the numbers are close to your body measurements, it is a body chart. If they are noticeably larger — or given as half-measurements across a flat garment — it is a garment chart.

The three that matter

Most fit failures come down to one of three measurements. Everything else is detail.

Chest or bust

Measure around the fullest part, with the tape level and snug but not pulling. For tops this is the single most predictive number.

For a garment chart, the flat chest measurement doubled is the garment's circumference. Subtract your own chest measurement and you have the ease — the room you have to move in. Roughly:

• 0–5cm — tight. Fitted shirts, base layers.
• 10–15cm — normal. Most t-shirts and casual shirts.
• 20cm+ — relaxed or oversized, deliberately.

A jumper with 5cm of ease will feel like a compression layer. One with 25cm will look like it belongs to someone else. Neither is wrong; both are choices you want to make on purpose.

Shoulder width

Measured seam to seam across the back. This is the measurement you cannot negotiate with. A shirt that is tight across the chest still buttons. A shirt whose shoulder seams sit two centimetres down your arm looks wrong from across the room and will not stop looking wrong.

Take this one off a garment you already own and like, rather than off your body — it is difficult to measure on yourself and easy to measure flat.

Length

Body length for tops, inside leg for trousers. Both are easy to check and both are common reasons something goes back.

For tops, measure from the highest point of the shoulder straight down. Compare against a garment you own. A three-centimetre difference is visible; five is a different silhouette.

Measure a garment you already own

This is the single most useful habit, and it takes five minutes.

Find something in your wardrobe that fits the way you want. Lay it flat, smooth out the wrinkles, and measure:

1. Chest — across, armpit seam to armpit seam.
2. Shoulders — seam to seam across the back.
3. Length — highest shoulder point straight down to the hem.
4. Sleeve — shoulder seam to cuff.

Write them down. Keep them in your phone. Now every size chart in the world is readable: you are comparing a garment to a garment, in the same units, measured the same way, instead of guessing what a brand means by "regular fit".

When the chart is between sizes

If you fall between two sizes, the tie-breaker is usually the fabric.

Something with stretch — anything with elastane, or a heavy jersey — will accommodate the smaller size. Something woven with no give — a cotton poplin shirt, rigid denim — will not, and the larger size is safer.

The second tie-breaker is what the garment is for. For a layer that goes over other clothes, size up. For something worn against the skin, size down.

What the chart will not tell you

A size chart describes dimensions, not shape. Two shirts with identical chest measurements can fit completely differently depending on where the fabric is cut away — a straight side seam versus a tapered one, a dropped shoulder versus a set-in one.

That is what "fit" names in a product description: slim, regular, relaxed, oversized. The chart gives you the size; the fit name gives you the shape. You need both, and a brand that gives you only one is asking you to guess.

The short version

• The letter is a marketing decision. The numbers are the garment.
• Check whether the chart gives body or garment measurements. They are not the same and the difference is often 15cm.
• Shoulder width is the measurement you cannot argue with.
• Measure something you already like and keep the numbers. It makes every other chart readable.