How to Measure Your Bra Size
Content editor
Nabeela SaghirHow to measure your bra size at home
Getting the right fit can change everything – comfort, confidence, and support. Here’s your quick-and-easy guide to checking your bra size at home.
Check your band: your underband should sit level around your body and feel comfortably snug (not tight). If it rides up, you might need a smaller band size.
Look at your cups: your boobs should sit smoothly inside the cups – no bulging or wrinkling. Spilling out? Try a bigger cup. Gaping or creasing? A smaller cup might fit better.
Front and centre: the centre of your bra should sit flat against your ribcage. If it’s lifting away, you need a bigger cup size.
Underwiring: wires shouldn’t poke, rub or press on breast tissue. If they do, a different size or style could make all the difference.
Strap check: straps should stay put without digging in. If they’re doing all the work, your band may be too big – a smaller band size can help share the load.
How to know your bra really fits
Getting the right fit starts with a few simple checks. Pay attention to your natural shape, how the bra sits on your body, and whether it feels comfortable throughout the day. Different styles and breast shapes can affect how a size fits, so putting a bra on and seeing how it feels is often more accurate than measurements alone.
What is sister sizing?
Sister sizing helps you find a better fit when your usual size doesn't feel quite right. These sizes have the same cup volume but bigger or smaller band widths.
The trick is to go down a band size, and go up a cup size – or the reverse. For example, a 34C has the same cup volume as a 32D or 36B because the cup works in relation to the band it sits on. If your band feels too tight or too loose, trying a sister size can keep the cup fit the same while giving you a more comfortably fitting band.
Bra fit FAQs
How do I find my bra size with a tape measure? You can use a tape measure to get a rough starting point for your bra size, but it won’t capture important factors like your breast shape, how a bra sits on your body and how it feels. For the most accurate and comfortable fit, we recommend having a professional bra fitting with one of our lingerie stylists.
What’s the most accurate way to find my bra size? The most accurate method is an in-person bra fitting. A fitter can assess how the band, cups, and straps work together to give you the best support.
Why do different bra styles fit differently? Every bra style – like plunge, balconette, or full cup – fits differently on the body. Your breast shape and support needs can also affect how a style feels, which is why measurements alone aren’t always enough to find the best‑fitting bra.
Should I trust online bra size calculators? Online calculators can help you start, but they’re not always precise. Trying a bra on or having a fitting gives a much more dependable result.
Why are my bra straps falling down? Straps can slip if they’re a little loose or if the cup size isn’t quite right. Sometimes it’s down to a bra’s design. Trying a different size or a style with closer‑set straps usually helps keep them in place.
Why are there bulges under my arm when I'm wearing my bra? Side bulges often mean the cup is a bit small or the style doesn’t give enough side support. Going up a cup size or choosing a style with more side coverage can help create a better fit.
Why are my boobs spilling out of my cups? If you’re spilling at the top or sides, the cup is too small. Going up a cup size or choosing a fuller‑coverage style will give you a smooth, secure fit.
How often should I have a bra fitting? We recommend every six to twelve months, or if you have recently lost or gained weight.
What if I’ve recently had surgery? After surgery, your body can feel a little different, and comfort becomes even more important. Soft, non‑wired bras are a great starting point until you’ve fully healed. We can also help refit you when you’re ready for a different style.
What if it's my first bra fitting? It’s completely natural to feel a little nervous about your first bra fitting, but our Lingerie Stylists are here to help you feel at ease. They’ll make sure you’re wearing the right size and style for your body. Using a simple visual assessment of your band, cup, and shape, our experts will guide you toward a fit that feels comfortable, supportive, and confidence‑boosting.
I only wear crop tops, so what bra size am I? Crop tops don’t always align with traditional bra sizes, so a simple fitting helps us determine your exact band and cup size. From there, we can recommend styles that still provide the support you need.
Published 09/04/2026
Related Stories

01/03/2025
Best bras for big busts
Discover our F to H bra range featuring non-wired bras and pretty balcony bras for bigger busts, and read on for expert advice for the perfect fit
Read more

01/03/2025
Confidence-boosting shapewear
Slip into something more comfortable: we have the best shapewear, from knickers to bras and bodies, in comfortable, modern, and flattering styles at M&S IE.
Read more

01/03/2025
The best period pants
Reusable period knickers are the latest lingerie innovation and could revolutionise your underwear drawer. Here, M&S lingerie expert Mhairi Leach explains how they work. Explore our range to find the perfect pair of period pants
Read more

28/01/2026
How to buy a sexy lingerie gift (and get it right)
Expert style and sizing tips for choosing sexy underwear gifts, from luxe lingerie sets to sultry slips
Read more




