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UK bra size calculator

There is so much advice out there on bra fitting. Every bra fitting guide seems to be a little different!

Whilst it is simple to take your measurements and use our UK bra size calculator. The difficult bit is knowing how your size and breast shape fit in various brands of sports bra.

Hence, bra fitting has veered away from just being about tape measurements. It now focuses more on assessing the fit of your current bras. 

Use our UK bra size calculator to figure out what ‘usual’ size is. Then the fun really starts! How do all the different brands and styles compare in terms of sizing? Is a Pure Lime bra 34D the same as a Freya 34D? 

This is why we try and test all our bras we stock. Our KnockerLocker reviews (under each product listing) reference how a single tester has found the fit of each bra we stock. It also gives her measurements and usual sizing.

Sometimes we have found the sizing of a particular brand or style to be really off kilter. In these cases we have put size converters in the bra images.

Keep reading to see how you can check if the size you wear is your correct fit. If you have really no clue- skip to the UK bra size calculator.

Overwhelmed? Want us to do the work?
Back Measurement
Bust Measurement

30A

30B

30C

30D

30DD

30E

30F

30FF

30G

30GG

30H

30HH

30J

32A

32B

32C

32D

32DD

32E

32F

32FF

32G

32H

32HH

32J

34A

34B

34C

34D

34DD

34E

34F

34FF

34G

34GG

34H

34HH

34J

36A

36B

36C

36D

36DD

36E

36F

36FF

36G

36GG

36H

36HH

36J

38A

38B

38C

38D

38DD

38E

38F

38FF

38G

38GG

38H

38HH

38J

40A

40B

40C

40D

40DD

40E

40F

40FF

40G

40GG

40H

40HH

40J

42A

42B

42C

42D

42DD

42E

42F

42FF

42G

42GG

42H

42HH

42J

44A

44B

44C

44D

44DD

44E

44F

44FF

44G

44GG

44H

44HH

46A

46B

46C

46D

46DD

46E

46F

46FF

46G

46GG

Sports bra fitting guide: Checking how your current bras fit

This is really the most important step in checking your bra size. It is vital that you check your current bra fit before buying new bras. It is easy to presume you are the same size as you were 1 year ago, 2 years ago, 10 years ago!

More than 80% of women wear the wrong bra size. If you have changed weight since you were last fitted, please make sure you do so before investing.

More than 50% of women suffer from breast pain. This is usually due to poorly fitting bras giving insufficient support.

20% of women suffer from ‘frictional breast injuries’- yep- chafing. Again caused by poor fitting, inappropriate bras.

poorly fitting bra- cups are too small
These cups are to small- breast tissue bulging out of top and into armpits

The Band

The band is the main source of support in the bra. Many women wear it too loose to avoid ‘back fat’. Or because they were once fitted with the ‘add 4 inches’ technique. DO NOT be tempted to adopt this approach in a sports bra!

The band should sit snug on your ribs. If it rides up at the back it is too loose. If you struggle to do it up on the loosest hooks, it is too tight. 

Raise your arms up and down, the band should not rise or move on your rib cage. Wearing your band too loose will mean you lose much support. This movement can also lead to chafing.

Cups

Your breasts should be fully enclosed within the cups. There should be no breast bulging out at the front or underneath the arms. There should be no bagging or unfilled areas.

Underwire

This should follow the natural crease of your breast. It should not sit directly on breast tissue.

Center Front

This is less relevant in sports bras- especially compression styles. In an underwired bra the centre front should sit flat against your chest wall. If there is a gap underneath try going up a cup size.

Straps

The shoulder straps should feel comfortable and should not be digging into your shoulders. They are there to keep the bra in place. The straps are not the main source of support.

If they are digging in, it is likely your underband is too loose and not providing enough support. You may then be tightening the shoulder straps to get the support you need.

Read a more in depth sports bra fitting guide in our blog.

Read the Locker reviews

There is considerable scope for error using a UK bra size calculator. Sometimes unfortunately there is no substitute for time in the fitting room.

We have tried all our bras with our KnockerRocker tester team. This information is in our Locker reviews on each product page.

You can help!! We are also aiming to build a library of your reviews. This will help other women find their best fit, first time.

When you fill in a review of your purchases, if you can add info such as: your usual size and how this bra compared. For example, bigger in the cup than expected. And finally- what Power Rating would you give it??

UK bra size calculator

If you really have no clue where to start then grab your measuring tape. Follow our guidelines and use our UK bra size calculator.

We would advise you do not rely solely on measurements & the result of our UK bra size calculator. Really checking the fit of your current bras is the vital part.

However it is always worth checking your back band size. A too large a band is the most common fit error- see below!

Step 1

Wear your ‘usual’ non- padded bra. Measure around where the under band goes around your ribs. 

It should be contacting your ribs all the way round, but not super tight. 

Write this down (A).

Step 2

Measure around the fullest part of your boobs. Make sure the tape is not slipping down at the back. It should not be pulled tight.

Write it down (B).

Step 3

Calculate B – A. Write it down. The difference equates to your cup size.

Example Band (A) = 34
Bust (B) = 38
B – A = 4

Refer to chart = D

Size 34D

Tip

If you measure an uneven number around the band- eg 33, just go for the band size up (eg 34)

Example Band (A) = 33

Bust (B) = 38

B – A = 5

Refer to chart = DD

Size 34DD

 

Top tips

If you have little fat around your ribs you may want to go up a back band size. So for example measuring 30 inches- go for a 32 band. 

Calculate your size using the method above using the ACTUAL rib measurement (eg 30) but then sister size down one cup size if you go for a looser band fitting.

Example: A = 30, B = 37

B – A = 7

Size 30F -> sister size 32E

AND Please....

DO NOT be tempted to routinely add 4 inches to your band measurement. This was from the 1950s when bras were made from silk and satin and did not stretch. The 4 inches extra allowed breathing room. All bras now have elastic and stretch in them. So please scrap this old technique!

Top Tips for sports bra fitting

Sister Sizing

Different combinations of back and cup size will give the same overall breast volume.

So, if your 38E bra is feeling loose around the back but fits well over your boobs: try dropping a back size and upping a cup size to give a 36F. The reverse is true also. Read more about bra sister sizing.

Sport bra specific fitting

According to a University of Portsmouth study, unsupported breasts can move up to 14cm during vigorous or strenuous exercise. This will lead to permanent stretching to the skin that holds your breasts in place and sagging.

There is now a huge variety of sports bras out there. The support you need for your sport of choice will be influenced by your breast size.  Your breast shape will influence the type of bra that will fit you best.

Refer to our Power Rating guide to find the right bras for you and your chosen sport. This combines your breast size with the impact level of your sport. It gives a rating of 1-5. Then just filter our bras accordingly.

Is sports bra sizing the same as normal bra size?

In theory, yes. However, it is not always as straightforward as that. Depending on the brand and the amount of support offered, the sizing metrics may differ.

Colour can even impact fit- often black fabrics have less give in them. Some brands or bras will be sized according to cup and band size. Some may use a scale from 0-8 or XS to XL+.

Which means you’ll then have to convert your bra size to its corresponding XS to XL+ size. Thankfully, there is usually a size chart for this, like the one from Enell.

How should a sports bra fit?

The overall fit should be snug but not too tight. It should not cut off your circulation or restrict your breathing. Both of these have been found to be detrimental to sporting performance.

Try jumping around a bit in your new sports bra to make sure it is comfortable. Check the band stays in place and you are able to move freely. You should feel supported and secure.

Jumping jacks are my test of choice, throw your energy into it and GO BIG- arms and all!

Just remember sports bras need replacing more frequently than everyday bras. Tests have shown after 25 wear/ wash cycles the support of the bra starts to deteriorate.

It will probably still feel pretty comfy, so it may not have popped onto your radar to replace at that point.