Bra Size Calculator
Fast, accurate and free online size biustonosza calculator tool running directly in your browser.
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1Enter data
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2Click the button
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3Get the result
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Choose the Perfect Size
Use the professional bra-fitting algorithm to find your comfort and self-confidence.
Enter the dimensions
To calculate the size, we need your current measurements in centimeters.
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Other tools you may find usefulBra size calculator - choose circumference and cup in a minute
Well-fitted a bra is not a "whim", but real everyday comfort: stable circumference, appropriate cup, better posture and less back or shoulder pain. Thisbra size calculatorhelps you quickly determine your size based on two simple measurements:underbust circumference i underbust circumference. You will receive the result in the standardEU(e.g. 75C), and you will also see equivalents inUK i US, the difference in circumference, body proportions andsister sizes- that is, alternatives that often save the situation when a specific model or the brand has a different stretch.
If you've ever had the feeling that "all bras are uncomfortable," it's very likely that the problem is the size (or the cut that doesn't fit the shape of your breasts). In practice, most bust support is provided by thecircumference, not the straps. When the circumference is too loose, the bra "moves" up, the straps start to pull, and the cups do not fit stably. In turn, a circumference that is too tight may cause pressure, calluses and breathing discomfort. Therefore, it is worth starting with measurement and approaching the selection calmly - using a calculator and then a short list of fit tests.
You enter two measurements and immediately get the EU size and UK/US and sister suggestions.
Sister sizes help when the band is too loose/tight or the brand has a different stretch.
You get the difference in circumference, type of construction and a simple interpretation of proportions - without jargon.
How to correctly measure underbust and bust circumference?
Measurement accuracy is extremely important. A difference of 1-2 cm is enough for the calculator to indicate the adjacent size. To measure, use a soft tape measure and stand straight in front of a mirror. It's best to measure on bare skin or in a very thin, non-padded bra.
1) Underbust circumference
- Place the measuring tapeparallel to the floor, just below the breasts.
- Measuretight but without pain- preferably on the exhale.
- Don't force it down. The circumference should hold you in place, but allow you to breathe freely.
This measurement largely determines thenumber in size(e.g. 70/75/80). This is the foundation of stability.
2) Bust
- Measure at thewidest part of thebreast, usually at the nipple level.
- The measuring cup should fit snugly, but not cut into the breasts.
- Breathe normally, do not tense your chest.
This measurement determines thecup size(A, B, C, D...). The cup size is the difference between the bust and circumference.
What does bra size mean? (EU/UK/US in practice)
A bra size usually consists ofcircumference(number) andcup(letter). Example:75C.
- 75– band: should lie stably on the loosest hook at the beginning of use.
- C– cup: depends on the difference between the bust and underbust circumference.
In different size systems, you will find different circumference markings. The calculator shows:EUas the main result (e.g. 75C) and the equivalents inUK i US. Many brands map A-D cups similarly, but larger cups often have letter differences (e.g. DD, E, F) depending on the manufacturer. Therefore, treat the result as a great starting point, and when shopping online, it is always worth taking a look at the chart of a specific brand.
Difference in circumference and body proportion - what do these statistics say?
After calculating the size, the tool shows two useful metrics:circumference difference(bust_diff) andunder/over proportion(proportion_ratio).
| Metric | What is it? | How to interpret this? |
|---|---|---|
| Difference in circumference | Bust circumference minus underbust circumference | This is the basis for calculating the cup size (the greater the difference, the "larger" the cup) |
| Under/over proportion | (under the bust / in the bust) × 100% | Proportion index – helps assess whether the figure is more "petite" or "fuller" in the upper part |
| Body type | Classification based on underbust circumference | Circumference fitting suggestion: petite/standard/wide |
In practice, these statistics have one purpose: to help you choose a bra not only "on paper", but also in real life. If you have a small underbust, you may be more likely to find models that are harder or less flexible - and then sister sizes do the job. If you have a wider circumference, the priority is the stability of the circumference band and the proper construction of the cup so that the weight of the bust is not transferred to the straps.
Sister sizes - the secret of comfort (and successful online shopping)
Sister sizes(sister sizes) are sizes that have a very similar cup "capacity", but a different circumference. This is useful because not every brand sews the circuits in the same way and the materials stretch differently. The calculator shows you two alternatives:
- Sister up- looser circumference, smaller cup size (e.g. 75D → 80C).
- Sister down– tighter circumference, larger cup letter (e.g. 75D → 70E).
5 Fit Tests You Should Do After Calculating Your Size
The calculator gives you a great starting point, but the "truth" comes out in the fitting room. Here is a short checklist:
- Girth: it should lie horizontally, not ride up on your back. At first, fasten with the loosest hook.
- Sternum: the center of the bra (breastbone) should be adjacent to the chest. If it sticks out, the cup is usually too small or the cut does not fit the shape of the breast.
- Cups: There should be no "overflow" or empty spaces. Delicate "things" on the sides may be a matter of cut, but a noticeable indentation is a sign that the cup is too small.
- Straps: they are supposed to stabilize, not carry. If you feel weight on your shoulders, the girth is probably not doing its job.
- Movement: make several movements (raise arms, bend, twist). The good size stays in place.
Common problems and quick size corrections
The circumference goes up
- Trya tighter circumference(sister size down).
- Choose a model with a stronger circuit band.
- Check if the straps are not too short.
The cup sticks out or wrinkles
- Possiblytoo large a cupor an inappropriate cut (e.g. full-cup vs. plunge).
- Try an adjacent cup down or another structure.
- Make sure that the breasts are properly "gathered" into the cups (scoop & swoop).
Cutting the cup ("double bust")
- Usually meanstoo small a cup.
- Try cup up or sister down (tighter band + larger cup).
- Choose a more full cut if the problem is at the top edge.
Shoulder pain from straps
- Check if the circumference is stable enough.
- Consider wider straps or a better constructed waistband.
- The straps should be snug, but not extremely tight.
How to choose a bra size? Measurement and size chart
For the bra size calculator to give an accurate result, you need two measurements taken with a soft tape measure:circumference under the bust(tight, but without the tape cutting in, on the exhale) andcircumference at the widest part of the bust(loose, in a slightly tilted position or in a thin, unpadded bra). The first measurement determines the circumference size (65, 70, 75...) and the difference between both measurements determines the cup letter.
| Underbust circumference (cm) | Size | Bust difference − under bust (cm) | Cup | |
|---|---|---|---|---|
| 63–67 | 65 | 12–14 | A | |
| 68–72 | 70 | 14–16 | B | |
| 73–77 | 75 | 16–18 | C | |
| 78–82 | 80 | 18–20 | D | |
| 83–87 | 85 | 20–22 | E | |
| 88–92 | 90 | 22–24 | F |
Example: under bust 73 cm, bust 90 cm. Circumference 75, difference 17 cm - cup C, i.e. size75C. If you enter "bra size calculator" in the search engine, the tool above implements exactly this scheme - with the advantage that it takes into account the limit values and immediately suggests sizes in the UK and US systems.
It is also worth knowingsister sizes: the volume of a 75C cup is the same as in 70D and 80B. When the bra in your calculated size has a good cup shape, but the band is too loose or too tight, go up or down one band size, changing the cup letter in the opposite direction. This is the most common solution when shopping online when a given size is out of stock - and the reason why a well-fitting bra does not always have the "obvious" size on the label.
FAQ – quick answers
Will the size from the calculator always be perfect?
This is the best starting point based on two measurements, but the perfect fit also depends on the cut, brand, elasticity of the material and breast shape. Therefore, it is worth using sister sizes and fit tests.
Why do I wear different sizes in different brands?
Because the stretchability of the circumference and the design of the cups differ between manufacturers. One brand has a harder band, another has a softer one, one sews deeper cups, another makes shallower ones. Sister sizes help you quickly "correct" the fit.
How often is it worth re-measuring yourself?
In case of major weight changes, after pregnancy, after changing physical activity, and also as a preventive measure every few months. The bra material also works - if the band has stretched, it may be time to replace it.
What if the bust circumference is only slightly larger than under the bust?
Then the cup may become very small (A/AA). Make sure that you measure the bust circumference at the widest point and that the tape measure does not slide down your back. If the result is confirmed, your circumference difference is simply smaller - and that's ok.
Summary: how to best use the
calculator. Enter two measurements in centimeters, click "Calculate size" and treat the result as astarting point. Then use sister sizes if you need circumference adjustments and make a short fit checklist. Thanks to this, you will find a bra that is stable, comfortable and looks good faster - without frustration and without hours of wandering around stores.
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