How to measure your bra size

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.