Bra Size Calculator

Created by Bogna Szyk and Aleksandra Zając, MD
Reviewed by Steven Wooding
Last updated: Apr 06, 2022

This bra size calculator can help you in finding and converting your bra size to most common international sizes — continental Europe, USA, and UK. If you ever wondered how to calculate your bra size according to European charts and what is the correct bra size for you (or your girlfriend 😀), keep reading to find out!

Taking measurements for correct bra size

You need to take two measurements. Take them while braless or while wearing a non-padded bra to ensure maximum accuracy of results.

  • Bust measurement: measure at the fullest point of your bust with a soft measuring tape. Make sure that the tape is not too tight by breathing in and out. Note the measurement down (if you decide to round it, remember to round the number up).
  • Frame measurement: measure around the bottom of the band, directly under your bust. Check whether the measuring tape is level and not too tight. Again, don't round the measurement or round it up to the nearest full number.

Looking for a bikini bra size? Try also our bikini calculator to check the bikini fashion that will flatter your body the most.

How to calculate bra size?

  1. First, take your measurements according to the rules listed above.
  2. Subtract your frame measurement from the bust measurement. This difference will determine your cup size.
  3. Compare your results with bra size charts. You can also use our bra calculator instead :)

In the table below, you can see, how the bust-frame difference determines the cup size.

Difference (inches [cm]) Cup size in the U.S. Cup size in Australia Cup size in the UK
1 (2.5) A A A
2 (5.1) B B B
3 (7.6) C C C
4 (10.2) D D D
5 (12.7) DD/E DD DD
6 (15.2) DDD/F E E
7 (17.8) DDDD/G F F
8 (20.3) H G FF
9 (22.9) I H G
10 (25.4) J I GG
11 (27.9) K J H
12 (30.5) L K HH
13 (33) M L J
14 (35.6) N M JJ
15 (38.1) O N K
16 (40.6) P O KK
17 (43.2) Q P L
18 (45.7) R LL

Sister sizes

Sister size is a relatively new yet very much needed term in the lingerie industry. Sister size means the bra size different from our original one, but with exactly the same cup. How is that possible, would you ask?

Manufacturers are not that generous, and they don't make separate cups for every combination of frame & cup possible. Instead, they make some cups, pair it with various bands and label bras with sizes. But counterintuitively, they don't label the same cups with the same letter — instead, they prefer to go one frame size down and one cup size up (or the other way around).

If that sounds complicated, don't worry. Take a look at the tables — all the bra sizes within the same color have the same size cup.

Sister sizes in the US chart

same row = same size
30A 28B
32A 30B 28C
34A 32B 30C 28D
36A 34B 32C 30D 28E
38A 36B 34C 32D 30E 28F
40A 38B 36C 34D 32E 30F
42A 40B 38C 36D 34E 32F
44A 42B 40C 38D 36E 34F
44B 42C 40D 38E 36F
44C 42D 40E 38F
44D 42E 40F
44E 42F

Sister sizes in Europe chart

same row = same size
65 70 75 80 85 90 95 100
65A 70AA
65B 70A 75AA
65D 70C 75B 80A 85AA
65E 70D 75C 80B 85A 90AA
65F 70E 75D 80C 85B 90A 95AA
65G 70F 75E 80D 85C 90B 95A 100AA
65H 70G 75F 80E 85D 90C 95B 100A
65I 70H 75G 80F 85E 90D 95C 100B
65J 70I 75H 80G 85F 90E 95D 100C
65K 70J 75I 80H 85G 90F 95E 100D
70K 75J 80I 85H 90G 95F 100E
75K 80J 85I 90H 95G 100F
80K 85J 90I 95H 100G
85K 90J 95I 100H
90K 95J 100I
95K 100J

Making sure your bra fits

Even if you have used our correct bra size calculator to find the proper size, it does not guarantee that every bra will fit. Use these tips to make sure you never buy a bad bra again!

  • Begin with putting your bra on properly. Bend forward at the waist, then put on the bra and hook it.
  • Adjust the band to make sure that the back of the bra is leveled with the front.
  • You should be able to slide only one finger underneath the band. If it is more loose, you should try on a smaller size.
  • After you tighten the band, shorten the straps.
  • Put on a close-fitting shirt over the bra to examine how it looks beneath clothing for a final check.
  • Choose a bra that fits perfectly when you secure the last hook. Your bra will loosen in time, so you will be able to make it fit you again by using the inner hooks later.

Make sure to check out our ideal weight calculator, too!

Wrong bra signs

Taking measurements is only the beginning, but nothing works better than your own experience. So, before buying a bra, we highly recommend you to try it on. The cups may be a different shape to what you're used to, the styles may make the bra sizes uneven — even among the same bra brand!
Check out this list — if you experience one or more of these signs, you're probably wearing the wrong size bra, or it is wrongly adjusted.

  • Red marks on the skin — either from straps or underwires. The first case means that either the straps are pulled too tight or the band of the bra doesn't support your bust enough. If an underwire pokes your skin, the cup is way too small.
  • Breasts spill from the bra — the cup is too small.
  • The cup sticks out — either the cup is too big, or this is not your bra type.
  • The band moves up on your back — the band is too loose. To offer support, the band needs to sit in one fixed position just under your bust.
  • The band feels tight — it's either the band is too tight, or the cup is too small. Try going a cup up first.
  • You suffer from the back pain or the neck pain — red flag! Your bra is not supporting your breasts at all. Try to adjust it as much as you can, but there is a 99% chance you'll need to buy a new one. Try our calculator first, or get a professional bra fitting in order to be as satisfied as possible with your purchase!

Bras for special tasks

Know your size already? Perfect! Now take a look at the most popular bra types and what can they offer to you.

I want to…

rock my attire tonight Push-upAdds a smooth line and even a size to your bust
Cage Gives you an intriguing cleavage
Stick-on The one and only for those backless evening dresses. Make sure to choose a good brand, so you can rely on the glue!
get comfy Non-padded brasNon-padded bras have an advantage over padded ones: they're simply softer
Wireless Less is more — the less stiff the bra elements, the more comfortable you are
get some special support Sports braBeing comfortable while exercising requires sound breast support
Maternity bra Allows you to breastfeed your baby without taking all your clothes off.

After capturing the perfect bra, there's time for perfect, made-to-measure clothes as well. Try our circle and pleated skirt calculators if you're in to sewing your own clothing. You can also take a look at the rest of our clothing calculators.


How to determine bra size?

To determine bra size, you need to:

  1. Measure your bust size with a soft measuring tape — do it while braless, and measure the fullest part of your bust.
  2. Measure your frame size — do it tightly, as the frame is the only genuinely supporting part of your bra.
  3. Your frame measure determines the size of the frame (the numeric symbol of the bra size).
  4. To count the cup size, do the subtraction: bust measurement — frame measurement.
  5. The result will determine your cup size. Check it according to the widely available cup size charts.
  6. Remember to check multiple bras (and sister sizes) in the lingerie shop, as finding the perfect bra is not a science and takes time and lots of trying on.

What are sister sizes?

While a popular belief is that cup size depends only on the size letter (e.g., that 32C, 34C, and 36C are the identical cups with longer band), the truth is different. The real cup size depends on the letter AND the band length. Bra sizes with the same actual cup volume are called sister sizes. This means that bra sizes 36B, 34C and 32D are sister sizes, and have the same cup.

You can check all the sister sizes in the sister size charts.

Whenever you're buying a new bra, it's always worth trying on various sister sizes to find your perfect fit.

What does bra size mean?

A bra size usually consists of two values — the numeric and letter one. The numeric one tells you about how long is the bra band (frame). It is system-adjusted so that it will differ around the countries. The value that doesn't change is the letter part of the size. It gives you an idea of how big the cup is. It goes up as the Latin alphabet; however, you will find DD instead of E and DDD instead of F in some American brands.

How to measure bra size?

  1. Measuring yourself to find a perfect bra size requires having a soft measuring tape.
  2. You should be braless while doing the measurements. It is also handy to have a mirror to check the tape position.
  3. Stand straight and measure your under bust. The tape should be on the same level all the way. Place the tape tightly and exhale while doing the measurement for the most accurate results. Note the measurement down.
  4. Now, measure the fullest part of your bust. This time, the tape should be much looser than while measuring for the frame. Check it breathing in and out and see if the tape lets you breathe comfortably.
  5. Note the second measure down. Now you're ready to go!

How to measure bra size without measuring tape?

Measuring bra size without measuring tape is a bit tricky but doable!

  1. Find a string. It could be a floss, some kind of a rope, or even a very thick thread.
  2. Then, find something with centimeters or inches calibration on it. It could be a ruler or a thick measuring tape (like that used for furniture). If you're in a real emergency, remember that a longer side of a standard US credit card measures precisely 3.5 inches and typical A4 paper size is 8-1/4 × 11-3/4 inches or 210 × 297 mm.
  3. Use your string to take your under bust measurement. You have to mark the measurements on your string; you could use a marker for that. If you can't do that, just keep holding the string with your fingers when you take it off and lay down the straight string on a flat surface, like a table of even floor. Mark the measurement with some object if you haven't done it with the marker before.
  4. Now, take an object with a known length (e.g., credit card) and see how many times it fits into your measurement by placing it near the string. Note the value down and multiply it by your known length.

Example: I fitted my credit card nine times, so I multiply 9 × 3.5" = 31.5". I round it up, and I find that my under bust size is 32.
5. Repeat steps 3-4, same with bust measurement.
6. By subtracting frame measurement from bust measurement (frame - bust), you get a difference that will indicate your cup size.
7. Pro-tip: if you've got some 'leftovers' of the string that you cannot measure with a known length no more, try to get creative. :) You can try to fit in the shorter border of the card — it's exactly 2 inches. You can also just estimate the rest length.

Bogna Szyk and Aleksandra Zając, MD
bra size calculator - measurements
Frame measurement
Bust measurement
In United States
Bra size
Cup size
In continental Europe
Bra size
Cup size
In United Kingdom
Bra size
Cup size
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