September 20265 MIN READ
Bra Fitting Guide: How Should a Bra Fit?
A great fitting bra should feel comfortable, supportive, and almost invisible under your clothes - unless you’re embracing the ‘underwear as outerwear’ trend, of course! However, many women are wearing bras that don’t fit as well as they could. While this is often linked to wearing the wrong size, it could also be because many of us aren’t sure how a well-fitting bra should actually feel and look.
The good news? You don’t need to be a bra-fitting expert to spot the signs. In this guide, we’ll walk you through the four key fit points so you can easily check if your bra is working with your body, not against it.
The Four Faithful Fit Features
When checking how your bra fits, focus on these four essential areas:
- Underband
- Straps
- Cups and wires
- Centre front
Each area plays an important role in comfort and support, and if even just one of these fit points isn’t sitting correctly, your bra may not feel or perform as it should.
How Your Bra Underband Should Fit
The underband is the foundation of the bra and is the area that provides most of the support. It should sit comfortably around your body, running horizontally across your back in line with the underwires at the front. A well-fitting underband should feel secure without digging into your skin or riding up at the back. You should be able to move comfortably throughout the day without constantly adjusting it.
If the band starts creeping upwards, feels loose, or shifts around as you move, then it's a sign the fit isn't quite right. Likewise, if it feels painfully tight or leaves deep marks, it may not be fitting comfortably.
How Your Bra Straps Should Sit
Your bra straps should stay comfortably on your shoulders without becoming something you constantly notice.
If your straps are slipping down, start by adjusting them to be tighter. Over time, bra straps naturally loosen with wear, so a quick tighten is often all that's needed. If they're still falling down after adjusting, or they're digging into your shoulders and leaving painful marks, your bra may not be providing support in the right places. While straps help lift and stabilise the cups, they shouldn't be doing all the work.
If you continue to experience problems after adjusting your straps, it may be worth checking your fit with our bra fitting guide or exploring sister sizing to find a more supportive fit.
How Your Bra Cups and Wires Should Fit
Your bra straps should stay comfortably on your shoulders without becoming something you constantly notice.
If your straps are slipping down, start by adjusting them to be tighter. Over time, bra straps naturally loosen with wear, so a quick tighten is often all that's needed. If they're still falling down after adjusting, or they're digging into your shoulders and leaving painful marks, your bra may not be providing support in the right places. While straps help lift and stabilise the cups, they shouldn't be doing all the work.
If you continue to experience problems after adjusting your straps, it may be worth checking your fit with our bra fitting guide or exploring sister sizing to find a more supportive fit.
How To Find Your Sister Bra Size
If your bra size is measured as a 34DD, but you’re finding the underband is too tight, then switching to a 36DD won’t solve the problem, as this will make the band and cup size bigger. Instead, you’ll need to adjust your cup size in alignment with the band size, to maintain the correct cup volume. Similarly, if you’re measured as a 34DD but the band is too big and not giving you the correct level of support, then switching to a 32DD won’t help much either! You would need to try the 32E to maintain the correct cup volume.
The easiest way to remember is, if you go up a band size, you need to go down a cup size. Or if you go down a band size, you need to go up a cup size.
Try using the Bra Sister Size Chart below to find your correct sizing alternative!
Bra Sister Size Chart
To use the chart, find your current size. If you need to go smaller, then choose the size to the left. Need to go bigger? Then choose the size to the right of your original measurement.
Will a Sister Size Feel the Same?
When first trying your bra sister size, it may take a few wears to adapt. Even though the cup volume is identical, the underband will feel different. The underband of your bra offers 80% of the support, so the band fit really matters. Sizing down to the tighter band will offer more support than sizing up to the looser band. If you’re still unsure, talk to one of our expert bra fitters in store who will be more than happy to help you find the best fit for you.
Bra Sister Sizes FAQs
How do bra sister sizes work?
Bra sister sizes work by using the cup-to-band ratio. When you go up a band size, you go down one cup letter to keep the same cup volume. Likewise, when you go down one band size, you go up one cup letter. This means the fit around your body changes, while the cup capacity stays the same.
Is it better to sister size up, or down?
It depends on the fit issue that you’re experiencing. If the band feels too tight but the cups feel good, then try the band size up. If the band feels too loose but the cups fit well, then try the sister size down. If the band and the cups don’t feel supportive and comfortable, then book a free bra fitting with one of our in-store experts.
How do I know which size bra to wear?
The best starting point is to take accurate measurements, as this helps you find your correct bra size. Knowing how to measure bra size properly provides a reliable foundation, but it's also important to remember that your bra sizing can change over time due to factors such as weight fluctuations, hormonal changes, pregnancy or simply ageing. That's why it's a good idea to check your size regularly, ideally every 6 months to a year.