Bra measurement Calculator
Find your perfect fit in US, UK, EU & AU sizes
Measure snugly but not tightly. Enter values below.
Sister sizes share the same cup volume. Go up a band size & down a cup, or down a band & up a cup, for a comparable fit.
Use a soft measuring tape for accurate results.
Wear the right bra
Measure in a non-padded, well-fitting bra (or without a bra). Avoid padded bras that add volume.
Measure your band (under-bust)
Wrap the tape firmly around your ribcage, directly under your bust. The tape should be snug but not tight. Note the number in inches or cm.
Measure your bust (over-bust)
Wrap the tape loosely around the fullest part of your chest, keeping it parallel to the ground. Breathe normally; don't compress the tissue.
Calculate the difference
Subtract the band measurement from the bust measurement. Each inch of difference = one cup size (A = 1", B = 2", C = 3", etc.).
Try on & adjust
Always try on the calculated size first. If the band rides up, go down a band size. If cups overflow, go up a cup. Consider sister sizes for comfort.
Bra Size Calculator —
Find Your Perfect Fit
The most accurate, free bra size calculator online. Enter your measurements in inches or centimeters and instantly get your size in US, UK, EU, and AU systems.
What Is a Bra Size Calculator — and Why Does It Matter?
Getting your bra size right changes everything about how a bra feels and performs. A bra size calculator does the maths for you — turning two simple measurements into an accurate, ready-to-shop size.
Studies from fitting experts suggest that a large proportion of women are wearing the wrong bra size on any given day. The reasons vary: sizes shift with weight changes, pregnancy, and age; brands size differently from one another; and many of us simply learned the wrong size early on and never revisited it. Using a reliable bra measurement calculator is the fastest way to reset that baseline.
Our free bra size calculator online takes just two measurements — your under-bust (band) and your over-bust (bust) — and converts them into your precise size across four major sizing systems: US, UK, EU, and Australian. It also generates your sister sizes and gives you practical fit tips based on your specific result.
Enter two numbers and get your full size profile in all major systems within seconds.
US, UK, EU, and AU conversions calculated simultaneously — ideal for international online shopping.
Toggle between bra size calculator inches and centimetres to match your measuring tape.
Discover alternative sizes with the same cup volume — useful when your exact size sells out.
How to Measure Bra Size at Home — Step by Step
Learning how to measure bra size step by step is a skill that takes less than five minutes and pays off every time you shop. All you need is a soft fabric measuring tape — the kind used for sewing — and a mirror. Here is the exact process our bra fitting calculator relies on.
What You Need Before You Start
Wear a non-padded, well-fitting bra — or measure without one if you prefer. Avoid heavily padded or push-up bras, as added padding gives inflated bust measurements. Stand up straight with your arms relaxed at your sides for both measurements.
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Measure Your Band Size (Under-Bust)
Wrap the measuring tape firmly around your ribcage, directly beneath your bust. The tape should sit flat and parallel to the floor all the way around — snug enough that it does not shift, but not so tight that it compresses your skin. Note this number. This is your underbust measurement.
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Measure Your Bust Size (Over-Bust)
Wrap the tape loosely around the fullest part of your chest, typically across the nipple line. Keep the tape parallel to the ground and breathe normally — do not inhale and hold, and do not compress the breast tissue. Note this number. This is your overbust measurement.
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Enter Both Numbers into the Calculator
Type your under-bust and bust measurements into the bra size calculator with measurements above. Select whether you measured in inches or centimetres, then tap "Calculate."
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Review Your Result and Sister Sizes
Your results show your recommended size plus sister size alternatives. Use these when shopping across brands or ordering from international retailers that use different sizing conventions.
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Try On and Fine-Tune
Always try on the calculated size. If the band rides up at the back, size down one band and up one cup. If the cups overflow or wrinkle, adjust cup size up or down accordingly. Fit is always the final test.
Measure yourself at the same time of day if you plan to compare measurements across weeks. Body measurements can shift slightly throughout the day depending on hydration, posture, and hormonal cycle. Morning measurements tend to be the most consistent baseline.
How to Measure Bra Size Without a Measuring Tape
If you do not have a fabric tape measure handy, you can use a length of string or ribbon. Wrap it around your body at the correct position, mark or cut the point where it meets, then lay it flat against a ruler or straight edge to read the measurement. A bra size calculator without measuring tape is also available via some smartphone apps that use your device camera — though these tend to be less precise than a direct measurement, they offer a useful starting estimate.
Understanding Cup Size and Band Size — The Full Picture
A bra size is made up of two components: the band number (the number) and the cup letter. Together they describe a unique fit. The band size calculator portion of this tool rounds your under-bust measurement to the nearest even number in inches, which is the standard US and UK convention. The cup size calculator works from the difference between bust and band measurements.
How Cup Size Is Calculated from the Difference
The difference between your over-bust and under-bust measurements, in inches, maps directly to a cup letter. This is the core logic behind every accurate bra size chart calculator:
| Difference (inches) | US Cup Size | UK Cup Size | EU Cup | Volume Description |
|---|---|---|---|---|
| < 1" | AA | AA | AA | Very petite |
| 1" | A | A | A | Petite |
| 2" | B | B | B | Moderate |
| 3" | C | C | C | Full moderate |
| 4" | D | D | D | Full |
| 5" | DD | DD | E | Very full |
| 6" | DDD / F | E | F | Plus full |
| 7" | G | F | G | Large full |
| 8" | H | FF | H | Very large |
| 9" | I | G | I | Extended full |
Cup size is not absolute — it is relative to band size. A 32D and a 38D have very different volumes. A 32D cup holds significantly less breast tissue than a 38D cup, even though both are called "D." This is why using a proper bust measurement calculator that accounts for both measurements simultaneously is essential.
Why Band Size Matters More Than You Think
The band provides approximately 80% of a bra's support. When the band is too loose, shoulder straps compensate — leading to strap dig-in, shoulder soreness, and the band riding up at the back. A correctly fitting band should feel snug but comfortable on the loosest hook when new, allowing you to tighten it as the fabric stretches over time. The band size calculator here rounds your measurement to the nearest even number, which is the standard for both US and UK sizing.
US vs UK vs EU Bra Sizing — Key Differences Explained
Shopping internationally means navigating multiple sizing conventions. Our international bra size calculator handles all conversions automatically, but understanding the differences helps you confirm results and shop with more confidence. This is especially useful when buying from UK-based lingerie brands that ship globally, or from European retailers using centimetre-based sizing.
- Band in even inches (28–54)
- Cups: AA, A, B, C, D, DD, DDD/F, G, H…
- DD and DDD most common at full end
- Used by Victoria's Secret, Wacoal, etc.
- Same band numbers as US (inches)
- Cups diverge after D: DD → E → F → FF → G…
- More granular cup system at fuller sizes
- Used by Marks & Spencer, Panache, Freya
- Band in centimetres (60, 65, 70, 75, 80…)
- Converted: under-bust (cm) + 15, rounded to 5
- Cup letters roughly match UK system
- Used by Triumph, Simone Pérèle, Aubade
- Largely mirrors UK sizing system
- Same band inch numbers, similar cup letters
- Cup divergence: DD → E → F → FF like UK
- Used by Berlei, Bonds, and local labels
Quick International Conversion Reference
When using the EU bra size converter or the bra size conversion chart calculator on this page, keep in mind that a 34C US is equivalent to a 34C UK, a 75C EU, and a 34C AU. The divergence grows significantly at fuller cup sizes — a US DDD corresponds to a UK E, which is why dedicated tools like this one are genuinely useful rather than optional.
Sister Sizes — Same Cup Volume, Different Band
One of the most practical concepts in bra fitting is the sister size. Every bra size belongs to a "sister size family" — a group of sizes that all hold the same cup volume despite having different band lengths and cup letters. Understanding sister sizes can solve a frustrating problem: when your exact perfect bra size is out of stock, a sister size delivers a comparable cup fit.
34C → 36B → 32D — these are all sister sizes. The 36B has a longer band but the same cup volume as the 34C. The 32D has a shorter band with the same cup volume. Move one band size up + one cup down, or one band size down + one cup up.
When to Use a Sister Size
- Your exact size is sold out online
- The band feels right but the cups are slightly off
- You are between band sizes during weight change
- Trying a new brand that runs differently
- Shopping the bra size calculator for shopping results
- The cups overflow slightly but you like the band
Our calculator automatically displays your three nearest sister sizes alongside your primary result. This makes it significantly easier to find bra size before buying online, especially from international retailers or boutique lingerie brands with limited stock.
Special Cases — Bra Size After Life Changes
Bra size is not fixed. It changes throughout life in response to weight shifts, hormonal changes, pregnancy, surgery, and age. Knowing how to know your correct bra size at each stage means remeasuring regularly rather than sticking to the number you have always used.
For a bra size calculator for teens finding their first bra, the same two measurements apply. Breast tissue continues developing through the mid-teens, so it is worth remeasuring every few months during this period. Start on the loosest hook to allow for growth.
The bra size calculator after pregnancy is one of the most frequently searched tools by new mothers. Cup size often increases 1–2 sizes during pregnancy, and band size can expand as the ribcage widens. Remeasure every trimester and again after breastfeeding ends.
Using a bra size calculator after weight loss is strongly recommended after losing or gaining 10+ pounds. Both breast tissue and ribcage dimensions change, often at different rates. Your band may decrease while your cup stays similar, or vice versa.
A sports bra size calculator uses the same base measurements, but sports bras typically run a half-to-full size smaller due to compression construction. Consider sizing up one cup when transitioning from a regular bra size to sports bra shopping.
Our plus size bra calculator works for all band sizes from 28 to 54 inches. Larger band sizes benefit most from full-coverage styles with wider straps, reinforced underwires, and boning in the side panels for better weight distribution.
If this is your first time using a bra size calculator for beginners, do not be surprised if your result looks different from what you have been wearing. Many people find they have been wearing the wrong size for years. Use the result as a starting point and fine-tune with try-ons.
Signs Your Bra Does Not Fit — and How to Fix Each One
The answer to "why is my bra size wrong?" often lies in the symptoms rather than the numbers. These fit signals tell you exactly what to adjust without needing to remeasure from scratch. Understanding how should a bra fit properly means recognising when something feels off and knowing what to change.
| What You Notice | Likely Cause | What to Try |
|---|---|---|
| Band rides up at the back | Band is too loose; band size too large | Go down one band size, up one cup size |
| Underwire sits on breast tissue | Cup too small; band too large | Go up one or two cup sizes |
| Cups gap or wrinkle | Cup too large for your volume | Go down one cup size; try different shape |
| Straps fall off shoulders | Straps too long; back band too loose | Shorten straps; try a smaller band size |
| Straps dig into shoulders | Band too loose; straps carrying all weight | Size down in band; check strap fit |
| Quadraboob (tissue over cups) | Cup far too small | Go up 1–2 cup sizes; try full-coverage |
| Side/back bulge around band | Band cutting into soft tissue; too tight | Go up one band size, down one cup |
| Centre gore does not lie flat | Cup too small or wrong shape | Try a larger cup or different style |
The Sports Bra vs Regular Bra Sizing Difference
When asking about sports bra vs regular bra sizing, the key distinction is compression. Regular bras encapsulate each breast individually. High-impact sports bras use compression to minimise movement. Because of this, sports bras tend to fit tighter — it is common to size up one band or cup when transitioning between the two types. If your regular bra is a 34C, your sports bra might be a comfortable 34D or 36C depending on the brand and impact level.
Use our free, accurate bra size calculator above — results in seconds, no account required.
↑ Calculate My Size FreeFrequently Asked Questions
The most accurate way to measure your bra size at home is with a soft fabric measuring tape. Take two measurements: your under-bust (directly beneath your bust, snug but not tight) and your over-bust (across the fullest part, tape parallel to the floor). Enter both into our bra size calculator with band and cup size above to get your result. Avoid measuring over bulky clothing, and wear a non-padded bra or measure without one.
With a 36-inch under-bust and 40-inch over-bust, your difference is 4 inches, which corresponds to a D cup. Your US bra size would be 36D. In UK sizing that is also 36D, in EU sizing approximately 85D, and in AU sizing 36D. Your sister sizes would be 34DD and 38C. You can confirm this with our calculator above.
Yes — our tool functions as both a bra size calculator cm and an inches calculator. Simply toggle the unit selector at the top of the calculator to centimetres before entering your measurements. The EU band size is calculated by adding 15 to your under-bust in centimetres and rounding to the nearest 5. All four size systems (US, UK, EU, AU) are shown regardless of which unit you measure in.
US and UK bra sizes are identical from AA through D. The divergence begins at DD. In US sizing, DD is followed by DDD (sometimes labeled F), then G, H, I, J. In UK sizing, DD is followed by E, F, FF, G, GG, H, HH, J — a more granular system. This is one reason why using an international bra size calculator is valuable when shopping from UK-based retailers, where a US DDD corresponds to a UK E.
Bra size changes substantially during and after pregnancy. Many women go up 1–3 cup sizes during pregnancy as breast tissue develops, and the rib cage often expands by 2–4 inches as well. During breastfeeding, cup size may fluctuate daily based on milk supply. After weaning, both breast volume and rib width typically settle at a new size different from pre-pregnancy. Using a bra size calculator after pregnancy every trimester and 3–6 months post-weaning gives the most accurate current size.
Bra sizing is not standardised across manufacturers. Even within the same nominal size, cups can be shallower or deeper, bands more or less stretchy, and underwires wider or narrower. A 34C from one brand may fit differently from a 34C from another. This is why understanding your sister sizes is so helpful — it gives you a range of sizes to try rather than one fixed number. Always check brand-specific fit guides when possible, especially when buying a new label.
Yes. This tool functions as a full lingerie size calculator and bra size calculator for shopping. Because it outputs sizes in US, UK, EU, and AU simultaneously, it is especially useful when shopping from international lingerie websites that list sizes in a different system from your own. Note your size in all four systems before you shop so you can match whichever format a retailer uses on their product pages.
There is no single answer — correct bra size for any person, including plus-size women, is determined by their own under-bust and over-bust measurements. Our plus size bra calculator covers band sizes from 28 to 54. Brands that specialise in fuller sizing include Elomi, Sculptresse, and Goddess for the UK market, and Glamorise, Torrid, and Lane Bryant for US sizing. Full-band styles with wider straps and reinforced construction tend to offer the best support at larger band and cup sizes.
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