20 Centimetres of Empty Waistband: What M&S, ASOS and Mango Assume Your Hips Are

You find the trousers. You take your usual size into the fitting room. They stop at your hips, so you go up a size. Now they go on, but the waistband stands away from your back and you can fit your hand down it.

You have probably been told, gently or otherwise, that this is something about your body. It is not. It is arithmetic, and the arithmetic is published on the brand's own website.

What we did

Every retailer publishes a size chart stating the body measurements each size is drafted for. Almost nobody reads them side by side.

In September 2026 we took the women's body measurement charts published by three retailers, Marks & Spencer, ASOS own-brand and Mango, and made one calculation for every size: hip measurement minus waist measurement.

That number is the waist-to-hip difference the brand has decided to cut for. It is the figure that decides whether trousers that fit your hips will also fit your waist. Here is what they assume.

Assumed waist-to-hip difference, in centimetres

Across all three brands and every size they publish, the assumed difference sits between 22 and 28 centimetres.

Our trousers are cut for 32 to 43 centimetres

We publish our own figure, because a customer cannot check a fit she cannot see. Here is the Hourglass Trouser.

Put the two ranges next to each other and there is no overlap anywhere. Our smallest waist-to-hip difference, 32 centimetres, is larger than the largest difference any of these three brands cuts for at any size.

If your body sits in that range, you have not been buying the wrong size. Those brands have no size drafted for your proportions. The number simply is not in their chart.

What it costs you, in centimetres

Here is the practical consequence. Take a woman, choose the size whose hip measurement matches hers, then read off the waist measurement that size comes with. The difference is what she has to gather with a belt, or pay a tailor to remove.

At the top of that range, the best-fitting M&S size leaves twenty centimetres of empty waistband. That is not a small adjustment. That is two hand widths of fabric with nothing in it, which is exactly why it folds over and stands away from your back.

ASOS uses one number for eleven sizes

One detail in the table above is worth sitting with. ASOS's own-brand chart holds the waist-to-hip difference at 25.5 centimetres for every size from a UK 4 to a UK 26.

That is the sizing method made visible. A base pattern is drawn, then the same increment is added to the waist and the hip at every step up. It produces a chart where a size 26 is assumed to have the same proportions as a size 4, only larger. Real bodies do not scale that way, which is why the same garment can work at one size and fail completely three sizes up.

We also noticed that ASOS lists a 63 centimetre waist at a UK 8 and a 72 centimetre waist at a UK 10, then 73 at a UK 12. A nine centimetre jump between two adjacent sizes, followed by a one centimetre jump, looks like an error rather than a design decision. We have left it in the table as published.

Next publishes no measurements for women at all

Two of the largest retailers we looked at could not be included, for a reason worth reporting on its own.

Next's women's size guide is a conversion table. It tells you that a UK 12 is an EU 40 and a US 8. It explains carefully how to measure your bust, waist and hips. It then gives you nothing to measure against. There is no centimetre figure for any women's size anywhere on the page.

The same page gives a waist measurement in centimetres for every men's jeans and trousers size. The childrenswear section gives height, head, chest and waist in centimetres, by year of age.

So a man can find out what a 32 means. A parent can find out what age 8 means. A woman is given a letter and told to hope.

H&M has no central women's size guide at all. Its sizing page directs you to open a product and look there.

What to do with your own number

Measure your waist at the narrowest point and your hips at the fullest point, standing with your feet together. Subtract the first from the second. That one number tells you more about whether a garment will fit you than the size on the label does.

If it comes to more than about 28 centimetres, you now know why the waistband gapes. If it comes to more than 32, you know why going up a size has never solved it.

Take that number with you. Ask brands what theirs is. Most cannot tell you, and that is the most useful thing you will learn.

Method

All figures were read on 26 September 2026 from each retailer's own published women's body measurement chart, not from garment measurements and not from third-party size guides. Mango publishes in inches on its UK site; those figures were converted at 2.54 centimetres to the inch and rounded to one decimal place. M&S states that its standard womenswear range is drafted for a height of 168 centimetres. ASOS states that its charts apply to ASOS own-brand clothing, not to other brands sold on the site.

This is three retailers, which is a small sample, and we are not presenting it as the whole industry. We chose these three because each publishes full body measurements in centimetres across its entire women's range, which turned out to be less common than we expected.

Sources: Marks & Spencer womenswear size guide; ASOS women’s clothing size charts; Mango size guide (GB); Next size guide; H&M sizing page. Our own measurements are published on every product page. Archived copies of the M&S, ASOS, Mango and Next pages are held on the Internet Archive, so every figure above, and the absence of figures on the Next page, can be checked independently even if a chart is later edited.

Earlier work on this subject that we drew on: Pudding.cool's February 2026 analysis of high-street jeans waistbands, and research from the Fashion Institute of Technology finding that only 23% of women are the same letter size across bust, waist and hips.

Questions

What is a waist to hip difference?

It is your hip measurement minus your waist measurement, in centimetres. If your waist is 73 cm and your hips are 110 cm, your waist-to-hip difference is 37 cm. It is the single most useful number for predicting whether trousers will fit you, and most brands do not publish theirs.

Why do trousers gape at the back of the waist?

Because the size that fits your hips was drafted for a larger waist than yours. When you size up to get the trousers over your hips, you take the waist measurement up with it. The excess fabric has nowhere to go, so it folds and stands away from your lower back. In the three brands we measured, a woman with a 43 cm waist-to-hip difference ends up with 13 to 20 cm of surplus waistband.

What waist to hip difference do most brands design for?

In the charts we checked, between 22 and 28 cm. M&S assumes 23 to 25 cm, ASOS own-brand a flat 25.5 cm at every size, and Mango 22 to 28 cm. Our own trousers are cut for 32 to 43 cm.

How do I measure my waist to hip difference?

Measure your natural waist at its narrowest point, keeping the tape level. Then measure your hips at the fullest point with your feet together. Measure against your body rather than over clothing. Subtract the waist from the hip.

Is a large waist to hip difference normal?

Yes. A difference of 30 cm or more is common and entirely ordinary. It is simply outside the range most size charts are built around, which is a fact about the charts rather than about the body.