S, M, L or XL? What Alpha Sizing Means in UK Sizes

There is no standard. That is the honest answer, and it is the reason this question is so frustrating.

Published UK alpha size guides commonly put a Medium at a UK 12 to 14. At Solta, a Medium is a UK 10 to 12. Same letter, different body. Neither of us is wrong, because the letter was never agreed between brands in the first place.

So if you have ever ordered a Medium that arrived too small, or too big, you did not misjudge your own body. You trusted a label that means something different in every shop.

Here is what the letter actually tells you, what it does not, and how to find your size in about two minutes with a tape measure.

Why S, M, L and XL cannot be converted like UK sizes

A UK 12 is defined by measurements. There is a published standard behind it, and although brands drift from it, there is something to drift from.

Alpha sizing has no such anchor. S, M, L and XL are groupings that each brand draws for itself, around the body it designs for. A brand cutting for a longer torso draws the lines in one place. A brand cutting for a fuller hip draws them somewhere else.

This is why you will find charts online that contradict each other, and why none of them settles the question. They are not badly made. They are describing different brands.

The same letter, two different bodies

Put two charts side by side and the gap is obvious.

Size	Typical UK alpha guide	Solta
S	UK 8 to 10	UK 8 to 10
M	UK 12 to 14	UK 10 to 12
L	UK 16 to 18	UK 12 to 14
XL	UK 20 to 22	UK 14 to 16

The two charts start together and separate as they go. By Large they are describing women four dress sizes apart, and by Extra Large, six. If you ordered by letter alone, that is the size of the mistake you could make.

Which is why the only number worth trusting is the one in centimetres.

What alpha sizing is good at

It would be easy to conclude that alpha sizing is just a worse system. It is not. It is a different trade.

Band and cup sizing is precise, and that precision is worth a great deal in a structured, underwired bra built to carry weight. It is less useful in a soft bra, a bralette or a knicker, where the fabric does the adapting and a rigid cup measurement describes something the garment does not actually have.

Brazilian lingerie is built around the second idea. The pattern is drawn from body measurements, the fabric is cut to move, and the fit is held by how the piece sits rather than by engineering in a cup. That is a design decision, not a simplification.

The honest summary: alpha sizing gives up precision at the top of the range and buys comfort and movement across it. For a D cup and under, in a soft piece, that is usually a good trade. For a fuller bust in a structured bra, band and cup earns its complexity.

The four numbers that replace the letter

Under bust, bust, waist and hip. Those four measurements work at every brand, in every country, for the rest of your life. The letter on the label does not.

If you have never taken them, or you are not certain you are holding the tape in the right place, we wrote the step by step separately: how to measure for alpha sizing. It takes about two minutes and you only need to do it once.

Once you have your four numbers, the chart below tells you where you sit with us.

Solta in UK sizes

Solta runs in four sizes, S, M, L and XL. These are our actual numbers, published rather than implied.

Solta	UK	Waist, cm	Hip, cm	Bust, cm
S	8 to 10	62 to 66	88 to 92	81 to 86
M	10 to 12	66 to 74	92 to 100	87 to 92
L	12 to 14	74 to 82	100 to 108	93 to 98
XL	14 to 16	82 to 86	108 to 112	99 to 105

The full chart, including conversions to EU and US band and cup sizes, is on our size guide.

Where P, M, G and GG come from

In Brazil the letters are P, M, G and GG, for pequeno, médio, grande and grande grande. It is the same four-step system under different initials, and it is the system our patterns were drawn in before they were ever translated for the UK.

That translation is the part most brands skip. A piece can be cut to a Brazilian pattern and sold with a UK letter on the label without anyone publishing what the letter stands for. If you want to understand why the word Brazilian means two completely different things on a UK label, we wrote about that in what Brazilian lingerie actually means.

If you are between two sizes

Go up.

A piece that is slightly loose settles into the body within a wear or two. A piece that is slightly tight marks the skin, and it does not improve. Elastic relaxes with wear, which works in your favour on the larger size and against you on the smaller one.

The exception is a soft bra you want for support rather than for comfort alone. There, go down on the band and up on the body, and if you are unsure, measure again sitting as well as standing. Ribcages change shape when you sit.

Frequently asked questions

Is a Medium a UK 12?
Sometimes. Published UK alpha guides often put Medium at a UK 12 to 14. At Solta a Medium is a UK 10 to 12. Check the brand's measurements in centimetres rather than assuming the letter.

What size am I in S, M, L or XL if I wear a 34B?
At Solta, a 34B is a Medium. At another brand it could be a Small. Compare your under bust and bust measurements against that brand's chart, because the letter alone will not tell you.

Does Solta make an XL?
Yes. Solta runs S, M, L and XL. Our XL is a UK 14 to 16, with a waist of 82 to 86 cm, a hip of 108 to 112 cm and a bust of 99 to 105 cm.

Why do brands use S, M, L and XL for bras at all?
Because in soft bras, bralettes and knickers the fabric adapts to the body, so a rigid cup measurement describes a structure the garment does not have. Alpha sizing fits how those pieces actually work.

Is alpha sizing less accurate than band and cup?
At the top of the size range, yes. Band and cup is more precise and that precision matters in a structured, underwired bra for a fuller bust. In softer pieces the difference is much smaller.

What are P, M, G and GG in UK sizes?
P is pequeno, our S. M is médio, our M. G is grande, our L. GG is grande grande, our XL. At Solta that is UK 8 to 10, UK 10 to 12, UK 12 to 14 and UK 14 to 16.

What should I do if I am between two sizes?
Go up. A piece that is slightly loose settles into the body. A piece that is slightly tight marks the skin and will not get more comfortable with wear.

What we would rather you did

Measure first. Then buy.

We publish our centimetres because a letter on its own is not information, it is a guess dressed up as one. If your measurements sit between two of our sizes, write to us before you order and we will tell you which one to take.

If you already know your size, our bras and knickers are cut to the numbers above.