How to measure your bra size

How to measure your bra size front fastening bra

Firstly, let’s just discuss the most common mistake women make with their bra fit. That being, they wear the band that runs along the rib cage way too loose.

Sadly in the US we find many inexperienced Bra Fitters (and bra fitting blogs!) adding unnecessary inches around the ribcage which lands the unfortunate customer (or blog reader) with a poorly fitted bra that has no chance of offering them support.

Bra measuring guide front opening bra

Before we go through how to measure your bra size, you absolutely need to understand that the band that runs around the ribcage is responsible for offering most of the support in the bra and as such this needs to be firm so that it can act as anchor for the front, the bust. You can read more about how a bra should and why here.

Ok, so let’s get started, let’s measure your bra size in these steps together!

Before you get started

  • Make sure you are wearing your “best fitted” bra
  • This bra should ideally be underwire and have minimal padding in it. Do not wear a push up style bra to take these measurements.
  • When measuring, stand in front of a mirror or have someone on hand to help so you can ensure your measuring tape is sitting evenly around your body.
  • Do not pull too tightly on the tape. The tape needs to be pulled firm enough to just stay in place without dropping.

Step 1: Take your ‘band size’ measurement

This is the measurement that leads us to the number component of the bra size eg the 34, 42 etc.

  1. Take a measurement, in inches, around the ribcage at the base of your bra.
  2. The tape should run evenly around your body, not dropping at the back.
  3. Record this measurement in inches.

For our example, let’s use the measurement 39.5″.

This 39.5″ means that the band size is a 40. You just need to round up to the nearest whole even number.

Here is a list of other measurements:

27 -28″ = 28 (a size 6 in some countries)

29 – 30″ = 30 (a size 8 in some countries)

31 – 32″ = 32 (a size 10 in some countries)

33 – 34″ = 34 (a size 12 in some countries)

35 – 36″ = 36 (a size 14 in some countries)

37 – 38″ = 38 (a size 16 in some countries)

39 – 40″ = 40 (a size 18 in some countries)

41- 42″ = 42 (a size 20 in some countries)

43 – 44″ = 44 (a size 22 in some countries)

45 – 46″ = 46 (a size 24 in some countries)

47 – 48″ = 48 (a size 26 in some countries)

49 – 50″ = 50 (a size 28 in some countries)

51 – 52″ = 52 (a size 30 in some countries)

53 – 54″ = 54 (a size 32 in some countries)

55 – 56″ = 56 (a size 34 in some countries)

57 – 58″ = 58 (a size 36 in some countries)

59 – 60″ = 60 (a size 38 in some countries)

Please do not add 4 inches to the measurement you get. This will have you purchasing a bra that is too loose to offer you support. Read O Magazine’s great articles on this.

In saying that, if you are between two size eg you measure 34.5″ it probably is safest to round up to the size 36 unless you like your bras very snug around your ribcage.

Step 2: Take your bust measurement

This is the measurement that we’ll use in the next step to determine the cup size.

  1. Take a measurement, in inches, around the broadest part of your bust. You may need to reposition your breast so that it is sitting well in the cup before taking this measurement.
  2. The measuring tape should sit firmly against your bust, but not too tight that is flattens your breast tissue.
  3. Record this measurement in inches.

For our example, lets use the measurement of 45″.

If you measure between inches eg 44.5″ then round up to the next whole eg 45″.

How to measure your bra size front fastening bra
A great example of how to take the bust measurement.

Step 3: Use these two measurements to determine your cup size

This step allows us to figure out the actual cup size, eg the A, DDD or G.

Calculate…. The Bust size measurement (step 2 measurement) MINUS the Band size determined.

In our example this is 45″ – 40 = 5.
Note that we are not minusing the two measurements, but rather the step 2 measurement from the step 1 determined band size.

We then use this number ‘5’ (in this case) to determine the cup size.

1 = A cup (less than 1 = AA)

2 = B cup

3 = C cup

4 = D cup

5 = DD cup

6 = DDD cup (or E cup in some countries)

Above 6 and it can get tricky, mainly because different countries have different cup size systems for beyond an American DD. So the following results are really a guide.

7 = EE/F cup

8 = F/FF

9 = FF/G

10 = G/GG/H

So… for the example we used (measuring 39.5″ and 45″) the bra size is a 18DD.

Important things to know

I never recommend making a big change to your bra size without the guidance of a bra fitter. So if you usually wear a size 24C and an online measuring guide is telling you that you are a 18E then exercise with caution. In this instance I would probably recommend making a small step in the right direction and to choose a size 22D or 20DD. This would mean you are working towards a firmer fitting band without making a huge jump that will more than likely end up in a disappointment.

Remember, that most women wear their band way too loose. The chances are, you may just do the same. Be honest with yourself about how your bra is fitting. If you are measuring smaller for your band size than what you are wearing ask yourself… Is this bra too loose? Or, would I feel better or worse with a firmer band? There is no point moving to a firmer (smaller) band if you feel like your existing bra is too firm.

As most women wear the wrong size bra it can be a challenge to move towards a better fitting bra, as it will feel very different! This is why we generally advise to take “baby steps” and work towards a better fit if the size you have been wearing is seriously wrong.

How a bra should fit

how a bra should fit front closure bra

how a bra should fit front closure bra

Are you like most women who still believe the support in a bra comes from the shoulder straps and the underwire?

There’s good reason women are attached to these beliefs. Firstly, this sort of information is still offered in department store change rooms and secondly the brands will also use persuasive language on swing tags advertising these as support solutions.

Understanding where the support comes from in a bra will help explain how a bra should fit…

In actual fact, the bra offers most of its support from the band that runs around our ribcage. This is used as a stabiliser of breast tissue. Just like the waist band on a hiking backpack is responsible for taking most of the load of the backpack, the band that runs around our ribcage is also responsible for taking the weight of the bust.

The underwire is there to offer shape, not support. Yes – you heard that right. The role of underwire is to round and separate the breast. It is not there to lift the breast nor stop the breast from bouncing while being active.

The straps that sit on the shoulders are also not in fact there for support, bur rather stability. Yes, we’ll feel less secure without them, but no they are not there to take the weight of the breasts. These straps are generally elastic which would be a tremendous design flaw should they be intended to support our heavy bust.

How should the underwire fit in a bra?

The underwire should not actually ever really touch breast tissue. It should run the whole way around the breast tissue and essentially sit against sternum, ribs and layers of subcutaneous fat.

Sometimes it’s not just the size that can cause an underwire to fit imperfectly in a bra, but also that the shape of the underwire is not right for the persons individual size attributes.

Some women will always struggle with having the underwire sit flush against the sternum (the bone between the two breasts) due to having their breast’s “close set” or just in general having a lot of breast tissue for their frame size. Of course, we want to get as close to perfect as possible, but it’s important not to get too hung up on this if you otherwise feel great in the bra.

How should the straps fit in a bra?

The bras shoulder straps are really there as a secondary layer of support, or as I generally say “stability. I once saw a study that suggested they do about 8% of the work. They shoulder straps should be firm enough to sit in place but not too tight to cause any discomfort across the shoulders.

Wide shoulder straps are always best as these will distribute any pressure more broadly across the shoulders. Shoulder straps that also have a significant amount of inelastic material work to offer more stability and result in a better overall lifespan.

How should the band that runs around the ribcage fit in a bra?

Now this is where the magic happens! This band needs to be firm enough to stay in place, and in line with the bust.

If this band is too loose it will simply find a broader part of the back to lodge in to, which is generally higher on our back. This then causes the sea-saw effect and has the bust sitting low and unsupported. This is simple physics, as the band rides up the back, the front will lower.

You want this band to be as firm as you can comfortably tolerate when the bra is new. Keeping in mind that with washing and wear the bra will stretch. It stretches mostly around this ribcage band which is why you should choose as firm a bra as you feel good in, so that when it does start stretching you don’t feel like it’s too loose to function.

When you first buy a bra the hook and eye clasps should be on the loosest setting. This will allow you to firm up the bra as this part stretches. This is actually why bras have three (or more!) settings – bra manufacturers know how important the ribcage band is.

Bra Fitting mistakes

The most common mistake we see women make with their bra fit is to have the ribcage band too loose, causing the bust to droop then resulting in them resorting to tighten the shoulder straps. This is a vicious cycle as this will only cause the back to ride up higher – after all, the bra band at the back is a whole lot lighter than the bust at the front.

The second most common mistake we see is that women choose a cup size too small. This will result in the underwire sitting against breast tissue, which is very uncomfortable, and also the breast tissue spilling out of the top of the cups.

Another mistake women often make is to buy a bra that feels comfortable on the tightest hook and eye setting. As mentioned above, this will then leave no room to tighten this very important part of the bra as it stretches yielding a un-functional product, quickly. So unless you are planning on gaining weight (pregnancy, teenagers or going in for surgery) you should never buy a bra that is set to the tightest or even the middle hook setting.