PRIMARK
Bra Fit Guide

Styling & Looks

How To Measure Your Bra Size: Your Bra Fit Guide

A perfect bra-finding masterclass, with bra fitting and sizing hacks

Feb 7 · 13 min read

How To Find Your Bra Size

Finding the right women’s bra size can be tricky. The truth is, there’s no magic formula to give you an exact answer because everyone’s body is different. But we do have a process for finding your starting size to make bra fitting faster and easier. Get a soft measuring tape ready and follow the simple steps below to find your size at home, making it easier to pick one when you're in the store. Or skip the lines and try them on in the comfort of your own bedroom by ordering with Click + Collect.

Bra Fit Guide

How to measure your bust size:

Your bust size is a measurement around the fullest point of your boobs, and is the first step to understanding the volume of your cups. Everything we measure for bras is in inches, so make sure your measuring tape has this scale (or get ready with your conversions...).

  • Stand in front of your mirror with a soft measuring tape, wearing either a non-padded bra that doesn’t constrict your chest or no bra at all.

  • Wrap the measuring tape around the fullest point of your bust, making sure it's straight around, parallel to the floor.

  • Make sure the tape is snug, but not pulled tight or digging in, and note the number on the tape.

  • Round this measurement to the nearest whole number and jot it down.

Bra Fit Guide
Bra Fit Guide

How to measure your bra band size:

Your band size relates directly to the underband of your bra — this is the number part of a bra size, usually from 28 to 42, using even numbers. It's the circumference of your rib cage in inches, so you can use the same method for measuring as before.

  • Stand in front of your mirror with a soft measuring tape, ideally wearing no bra at all or a non-wired bra.

  • Wrap the measuring tape around your rib cage at the level where your breast meets your ribs, parallel to the floor.

  • Note the number, rounding it to the nearest whole number. If it's an odd number, round it up to the nearest even number — and that’s your bra band size!

Bra Fit Guide

How to find your cup size:

So now you have these two measurements, there's some simple math to calculate your approximate cup size. Just subtract your band size from your bust size. The difference between the two in inches is your cup size. The cup size of a bra is the letter part, usually anywhere from AA to G in most collections. Each inch of difference between your measurements correlates to a cup size, as below.

Cup Size Measurement Chart

0 inches – AA

1 inch – A

2 inches – B

3 inches – C

4 inches – D

5 inches – DD

6 inches – E

This continues in one-inch increments for all other cup sizes. For example: if your bust is 35 inches and your band size is 32 inches, you have a 3-inch difference, meaning you’re a cup size C. Your bra size then would be the combination of your band measurement and your cup size. So in the above case, the cup size is C and the band size is 32, making that person a 32C. Simple!

Bra Fit Guide
Bra Fit Guide

If you’ve figured out your bra size from the above, it might seem like that’s the end of it. But it’s important that you know how to correctly fit a bra, because this guideline size isn’t always 100% accurate. The reason fitting a bra is so important is because the above measurements don’t account for how breast tissue is distributed on each person’s body, or the shape of your boobs. We also have round up the above figures to their nearest whole numbers, which reduces accuracy. Some other things that might impact your bra size are the styles you pick, the fabrics the bra is made with (some may be stretchier than others), and even the brand you're buying, because there can be slight differences between companies in the way the bras are sized. We always recommend trying on and testing the fit of each bra you buy to make sure you’re always comfortable and correctly supported. It’s worth the extra time to get the most out of your bras!

Bra Fit Guide

How To Make Sure Your Bra Size Is Correct

The first step to making sure your bra fits correctly is making sure that it's on the right way.. When putting on a bra, follow the steps below to make sure everything is in its place to get a more accurate understanding of your fit. This is how you should put your bra on every day, not just before bra fittings!

  • Fasten the bra at the rear on the loosest hooks – bras lose elasticity over time, so you need the tighter hooks to be able to keep it snug and make sure it lasts longer.

  • Pull up your straps, making sure they're sitting parallel to each other, adjusting the tightness as needed.

  • Lean forward to let your breast tissue sit fully in the cups, scooping from either side so that no tissue is being pushed under your arms.

  • Pull your underwires into place, making sure no breast tissue is between your underwire and your ribs, and that your underwire is sitting at the point where your breast meets your rib cage.

Once you're sure the bra is on correctly, we recommend checking the fit in this order to identify any issues.

  • Start with your straps – check they're comfortable, and you can fit two fingers between the strap and your skin easily, but not loose enough that you can fit more.

  • Pull at the back of your underband with your thumb – it should pull away from the skin, but not feel slack or loose.

  • Look at the cups – they should sit flat against your breast tissue with no bulging, gaping, or dimpling. All breast tissue should be inside the cups with no visible spillage around the cups or behind the wires.

  • Check the wires – underwires should sit completely flat against your ribcage with no gaping at the center or sides, and shouldn’t be digging in or sitting on top of breast tissue.

Bra Fit Guide
Bra Fit Guide

4 Ways To Identify Badly Fitting Bras

It’s easiest to see when there's something wrong with a bra and tackle those issues to find the perfect fit. The telltale signs a bra isn’t fitting right are:

  • Bra straps hurt the shoulders or keep falling down

If your bra straps are too tight, they can cause discomfort from pulling the cups too tight on chest as well as restricting your shoulders and back. Adjust them so they fit without causing red marks, but not loose enough that they fall down your shoulder.

  • Bra riding up the back or pinching skin

If the bra band's too loose, it will ride up at the back where it's not correctly anchoring the bra in place. This can cause spillage, might require you tightening your straps, and can even cause backaches because your bust isn't being supported correctly. The solution: reduce your band size.

So: how tight should bra bands be? Tight bands can cause skin chafing and tightness on your chest and back. It’s important that the band firm but comfortable. If you feel restricted uncomfortably by your underband, go up a size.

  • Bra side spillage or gaps

How should a bra cup fit? Your boobs should fit snugly into the cups without squashing your skin or leaving red marks, with the cups sitting flat and no visible dimpling in the fabric.

If your breast tissue is spilling at the top or sides of your cups, or the underwires are sitting on top of breast tissue, the cup is probably too small and you should size up. If your cup is gaping at the top and side of your bra or the fabric is wrinkling, your cup may be too large and you should size down.

  • Underwire bra hurts, or wires sit away from the body

Underwires, while structured, are not supposed to be uncomfortable and are supposed to sit directly on your rib cage. If your underwires are digging uncomfortably into your underarms, you might need to try a smaller cup size. If your underwires are digging into your breast tissue, you might need a bigger cup size. If your underwires are not sitting flat to your sternum (your breastbone) and are hanging away from the body, you need a larger cup size.

Here’s our handy video explaining how to measure your bra size:

What Is A Sister Bra Size?

Sister sizes are two different bra sizes that have the same cup capacity, but a different band size. This is essential to know when adjusting your bra size during a fitting to save you time in getting the best possible fit. If you change your band size, you need to adjust the cup size too, so it still fits correctly. For example: if you need to go down in your band size, to accommodate this change you’d go up in your cup size.

Sister sizing examples would be:

  • 32C becomes a 34B if you increase the band size, or a 30D if you decrease the band size.

  • 36F becomes a 34G if you decrease the band size or a 38E if you increase the band size.

Bra Fit Guide
Bra Fit Guide

Maternity Bra Size Guide

Maternity and nursing bras fit ever so slightly differently to your regular bra — and for good reason, because your body will change a lot in this time. When you’re looking for the perfect fit for a maternity bra, here are the things to keep in mind:

Wires

  • It isn’t recommended that you wear underwire bras later in pregnancy. So if you’re looking at a nursing bra with underwires, we recommend talking with your doctor or waiting until after birth to begin wearing it.

Straps

  • Maternity bras feature wide, comfortable straps for additional support. If the straps has clips it's a nursing bra, designed for ease when breastfeeding. Make sure you know which you’re looking for: not all maternity styles are nursing bras.

Cup Size

  • During your pregnancy and after birth, your cup size is likely to increase and fluctuate. We recommend buying your nursing bra with extra room to accommodate this change, either by going up a cup size or checking to see if you can fit your hand comfortably into the cup when it's on your body.

Band Size

  • Most maternity bras come with extra hook-and-eye loops so you can adjust the bra more effectively, because your underband size expands during pregnancy then reduces after birth. If you’ll be wearing the bra throughout your pregnancy, we recommend fitting it on the middle hook for adjustability in both directions. Or if you’re buying it for nursing, we recommend fitting it to the loosest hook.

Post-Surgery Bra Size Guide

The best post-surgery bras are designed to provide support and comfort to those who have recently undergone surgery. They're different from regular bras: they have a front closure, wider straps, more coverage, pockets for prosthesis and softer fabrics to be gentle on delicate skin. If measuring your post-surgical bra before your operation, we recommend you buy a bra 1-2 bra band sizes larger than you normally would; this accommodates post-surgical swelling.

FAQs

Why does my bra strap keep falling down?

  • If your bra strap falls, this could be due to the strap tightness or the bra style. Bra straps should fit comfortably on your shoulder without leaving red marks or slipping down your shoulder, and might need tightening to prevent this. However, falling bra straps may also mean you have sloping shoulders, so pick bras with wide straps or with a racer back that holds the straps firmly in place. And avoid styles like balcony bras which have wider-set straps.

How do I know if a bra fits?

  • A well-fitting bra is comfortable and offers support without chafing, squashing your skin, leaving red marks, causing spillage or back pain. The bra band should fit flush to your skin and never ride up your back. Your boob should fit snugly against the cup. Underwire bras shouldn't dig into your skin or poke your underarms, sitting flat against your ribs.

How do I fix gaping cups?

  • If your bra is causing gaping at the top or sides, you might be wearing the wrong cup size. Try and tighten the bra straps, making sure the bra band stays straight across your back. If the band rides up or if you’re still getting gaps, we recommend going down a cup size.

Why do my boobs come out of the bottom of my bra?

  • If your breast tissue is spilling below your underwires or the bottom of the bra, your underband is probably too loose. You might need to size down to avoid it riding up over breast tissue. If you reduce the underband size and your underwires still sit on the breast tissue, you may need to wear a larger cup size.

Why is my bra riding up my back?

  • If your bra is riding up your back, your underband is probably too loose. We recommend sizing down in your underband and making sure that the straps aren’t too tight, causing it to lift.

Why does the underwire in my bra hurt?

  • If your underwire hurts, you might be wearing the wrong bra size or a style that isn’t comfortable for your body. Try adjusting your cup size and band size until the fit feels right. If the underwires dig into the center of your chest or under your arms, try a style with a smaller wire like a plunge bra.

Why doesn’t the center of my bra lie flat against my chest?

  • If the centre of your bra isn’t sitting flat, your bra cups are probably too small. We recommend trying a larger cup size and making sure that the underband is secure to avoid it being pulled away from your ribs.

Why does my bra ride up when I lift my arms?

  • A bra riding up and not staying in place is a sign that your underband is too loose. Try sizing down on your underband to make sure it can correctly hold the bra in place against your body. It’s also worth checking that your straps aren’t too tight.

Why do my bra cups wrinkle?

  • Wrinkled cups are a sign your breast tissue isn’t completely filling your cup, which may be too large. We recommend trying a smaller cup size to make sure the cup sits flush against your boobs without extra room.