M&S Bra Sizes and Fitting, Explained

The M&S fitting service at a glance

• Cost: free, with no obligation to buy.
• Where: in stores with a lingerie department. M&S has said it has around 5,000 trained fitters.
• Booking: online through its bra fit booking tool, or by asking in store. Walk-ins depend on how busy the store is.
• How often: M&S recommends a fitting every six to twelve months.

M&S described its position in a 2022 announcement as holding 37.5% of the UK bra market. Whatever the current figure, a very large share of British women have been fitted there, which is why "M&S told me I was a…" is such a common starting point.

M&S online sizing tools

M&S provides bra fit guidance on its website alongside its booking tool. Like any retailer's tool, it is designed to place you in a size within M&S's own ranges.

If you use it, compare what it tells you with a direct measurement. Measure your underbust, round to the nearest even number, and see whether the band you are offered matches. If the suggested band is two or more inches bigger than your underbust measurement, try the band below as well. Our calculator shows its working, so you can see where any difference comes from. For why two tools can disagree, see how accurate bra size calculators are.

What to expect at an in-store fitting

You will be shown to a private fitting room. The fitter will ask what you are looking for and what bothers you about your current bras, establish a size to start from, and bring bras for you to try. They should then check each bra on you and adjust the size or style.

You can ask the fitter to wait outside while you change, and you can keep a top on between bras. Say so at the start and they will work around it.

How to get a good result

1. Measure at home first. Go in knowing your underbust and bust measurements and your starting size.
2. Tell the fitter your measurements and ask to try that size along with whatever they suggest.
3. Try the band below. If you are offered a 36, ask for the 34 with one cup letter up. It costs nothing to compare.
4. Do the checks yourself. Fasten on the loosest hook, scoop and swoop, then look at the band, the cups and the centre panel. The full list is in how a bra should fit, and there is a printable fitting checklist to take with you.
5. Try more than one range. Different M&S lines are cut differently, and the same size will not fit the same way in all of them.

"M&S measured me wrong"

Search any parenting or fashion forum and you will find people saying this, usually after being fitted elsewhere and coming out in a smaller band and larger cup. You will also find plenty of people who were fitted well. With thousands of fitters across hundreds of stores, experiences are bound to vary, and people who are unhappy are more likely to post.

The complaint that comes up most is a band that turned out to be too loose. That is the error research has linked to tape-measure fitting with the traditional formula: a University of Portsmouth study found that method tended to overestimate band size and underestimate cup size. We cannot tell you how any individual M&S fitter works, and methods differ from person to person. What you can do is check the outcome.

Signs the size you were given is off

• The band sits higher at the back than at the front.
• The bra is new and you already need the middle or tightest hook.
• The straps dig in, or you keep shortening them.
• The centre panel does not rest flat on your breastbone.
• There is a slight bulge over the top of the cup, or the wire sits on tissue at the side.

If two or more of these apply, the usual correction is one band down and one or two cup letters up. Someone given a 36C would try a 34D first, then a 34DD. The sister size chart shows the equivalents, and why your bra rides up at the back explains the reasoning.

M&S size range and its limits

M&S covers the centre of the size chart very thoroughly and stretches a good way towards the edges. The exact range is set per style, so a size offered in one bra may not exist in the one next to it on the rail.

That matters for one reason. A shop can only fit you into what it stocks. If your true size is at or beyond the edge of a retailer's range, a fitter may place you in the nearest size available, typically a bigger band with a smaller cup letter. If you suspect that has happened, measure yourself and see whether your result falls outside what the store sells. A full-bust specialist will carry it. See the best places for a bra fitting in the UK.

Other retailers

For comparison, see our guides to the John Lewis fitting service, Boux Avenue, Primark and Ann Summers, and the head-to-head Bravissimo vs M&S sizing.

Who M&S suits best

• It suits you well if you are in the middle of the size range, want affordable everyday bras, and value having a store nearby with free fittings and easy returns.
• Look further if you need a 28 or 30 band, a cup well above G, or a particular cup shape that M&S ranges do not offer. Specialist brands give more choice there.

Frequently asked questions

Is the M&S bra fitting free?

Yes. M&S offers bra fittings in its stores at no charge and with no obligation to buy. Booking ahead through the M&S website or app is the surest way to get a slot at a busy store.

Are M&S bras true to size?

There is no single answer, because M&S sells many ranges and they are not all cut alike. Start with your measured size, try the neighbouring sizes as well, and judge by the fit checks. If you were sized using added inches, your true size is likely to be a smaller band and a larger cup than you were given.

Why did M&S give me a different size from this calculator?

Sizes differ when the methods differ. Our calculator uses your underbust measurement directly. If a fitting or size guide arrives at a bigger band, check the result against how the band behaves on you: a band that rides up or needs the tightest hook is too big, whoever suggested it.

Does M&S sell small bands and large cups?

M&S covers a broad span of sizes, and the range differs from style to style. Availability is thinner at the edges, such as bands under 32 or cups above G. Check the size list on the individual product, and look at full-bust specialists if your size is not offered.