Bra AtlasBra sizing, measured and sourced

Bra size calculator: your size from two measurements

Bra sizing is messy. Two calculators, two answers, and somehow neither is the size that actually fits. Let's sort it out together. Two tape measurements, your size in US and UK labels, its sister sizes, and what to try if the first bra doesn't fit. Got a different answer elsewhere? We'll show you why.

Take your time. Two tape measurements and a quiet minute is all this asks. Pick the woman who looks like you.

Your measurements

How to measure this
Illustration of a woman with light skin and straight black hair, with a level measuring tape directly under the bust, where the bra band sits.

Wrap the tape around your ribcage where a bra band sits, directly under your bust. Pull it snug, keep it level all the way round (a mirror helps), breathe out, then read it.

How to measure this
Illustration of an older woman with short silver hair, with a loose measuring tape around the fullest part of the bust.

Keep the tape loose and level, resting on the skin without pressing in. If you also take a leaning reading, keep it separate; the measuring guide explains how to compare readings.

Private. Measurements you enter here are calculated in your browser, not sent or saved by the calculator. How we check

Your fitting card will arrive here like a note from a friend: your size in US and UK labels, its sister sizes, and what to try next.

1 Underbust snug and level 2 Bust loose at the fullest point
An illustrated woman in a bra who follows your measurements. Shown: a woman with warm brown skin and long straight black hair in an ivory bra.
An example drawing until both numbers are in. She follows yours as you enter them.
Which of us feels like you?

Only the drawing changes. Your size comes from your two measurements.

By Rai Ansar · Sizes computed by the Bra Atlas engine · Sources and checked dates · How the sizes are calculated

  • Checked, not guessed. Matches the recorded A Bra That Fits results for 18 synthetic pairs in five label systems. Fixture checks, not a claim that the two calculators use the same method. See how

  • Private. Your measurements stay in your browser. Not saved, not sent, no sign-up.

  • Independent. No ads are served here. Brand comparisons cite their charts, and Amazon links are labeled.

  • Honest about limits. This is a starting size, not a fitting. Both methods are shown, with why they differ.

Already own a bra that feels wrong? The fit check starts from the size you wear and tells you which way to move.

Built and maintained by Rai Ansar. The calculations share one sizing engine, and fit advice links to its sources.

How to measure

How to find your bra size at home, step by step, with a soft tape and a mirror. Wear an unlined bra or none, and keep the tape comfortable rather than tight.

Illustration of a woman with light skin and straight black hair, with a level measuring tape directly under the bust, where the bra band sits.
Underbust: snug, level, directly below the bust.
Illustration of an older woman with short silver hair, with a loose measuring tape around the fullest part of the bust.
Bust: loose, level, around the fullest point.
  1. Underbust. Stand straight, arms down. Wrap the tape around your ribcage directly under the bust, where a bra band sits. Keep it level at the back (check in a mirror), pull it snug, breathe out and read it.
  2. Bust. Wrap the tape around the fullest part of the bust. Keep it level and resting on the skin without pressing in. Start with a standing reading. A Bra That Fits also asks for leaning and lying readings; keep those separate rather than automatically choosing the largest. Our measuring guide explains the difference between the two-input estimate and that six-input method.
  3. Enter both. Use the same unit for both. Half inches are fine; the calculator shows two letters when you sit between cups.

Full step-by-step guide, with the mistakes that throw the result off: how to measure your bra size.

Not sure what the letter means? The cup sizes guide explains what each cup letter means and where UK and US letters part after DD.

Prefer a table? The bra size chart lists the bust measurement for each US band from 28 to 46 and cup from AA to H, in inches with a centimeter option, then the same sizes on UK, EU, French, Australian and Japanese labels.

What we measured

Ten tape measurements, run through two public calculators and our engine on 25 September 2026. Our UK results match A Bra That Fits on all ten recorded pairs.

Same tape, three answersUK sizes. A Bra That Fits and calculator.net were run with the exact numbers in the first two columns; the +4 column is our padded-band comparison, not calculator.net's own +4 output.
UnderbustBustBra AtlasA Bra That Fitscalculator.net+4 method (US)
28 in30 in28B28B28B32AA
30 in34 in30D30D30D34AA
32 in35 in32C32C32C36AA
33 in37 in34C/D34C/D34D38AA
34 in38 in34D34D34D38AA
36 in41 in36DD36DD36DD40A
38 in44 in38E38E38E42B
29 in33 in30C/D30C/D30D34AA
40 in46 in40E40E40E44B
42 in48 in42E42E42E46B

Highlighted rows are where calculator.net disagrees: both have an odd underbust (33 in and 29 in). Read the 18-pair A Bra That Fits capture and calculator.net output labels. These are synthetic checks; Japanese labels are not claimed to match exactly.

What your result includes

A worked example: 33 in underbust, 37 in bust. Type the same numbers into the calculator to get the fitting card, the shop link and this table for your own tape.

Open this example in the calculator

33 in sits between the 32 and 34 bands, so the answer is a range, 34C/D, and both letters are worth trying. Under the size, the calculator lists its sister sizes (same cup volume, different band) and the size to try next for each thing a first fitting can show, all relabeled in UK, US, EU and AU.

32D: band 32 in, same cup volume. Shown: a woman with olive skin and long dark waves in a lilac bra.

32D

tighter band

34C: band 34 in, same cup volume. Shown: a woman with light skin and straight black hair with a fringe in a sage bra.

34C

example size

36B: band 36 in, same cup volume. Shown: a woman with deep brown skin and a rounded afro in a rose bra.

36B

looser band

Same cups, three bands: 32D, 34C, 36B hold the same cup volume.

Shown for 34C, the smaller cup in this example's 34C/D range. Illustrations explain the size relationship, not a predicted body shape.

Worked example: sister sizes and what to try nextFrom 34C/D: the same size relabeled for four systems, and the size to try for each thing a first fitting can show.
If you noticeUKUSEUAU / NZ
Band rides upTighter sister: band down 2 in, same cups32D/DD32D/DD70D/E10D/DD
Your sizeTry this first34C/D34C/D75C/D12C/D
Band digs inLooser sister: band up 2 in, same cups36B/C36B/C80B/C14B/C
Spilling outOne cup up, same band34D/DD34D/DD75D/E12D/DD
Gaps in the cupsOne cup down, same band34B/C34B/C75B/C12B/C

The moves are the ones the fit check uses, from the same code: a band that rides up means one band down with the same cups; spilling means one cup up on the same band; and so on. They are a fitter's rules of thumb, not a guarantee, and brands cut differently.

Brands disagree too

The same tape, 34 in underbust and 38 in bust, through three brands' own tools on 25 September 2026. Their band padding is why.

34DBra Atlas, measured band
36BWacoal calculator
36AThirdLove calculator
38ASKIMS chart

Wacoal and ThirdLove from their online calculators, SKIMS read off its published chart. Each is a starting point for that brand's own cut, not a different body. How each brand's chart works.

Why two calculators give you two sizes

The methodology behind every number on this site, in full.

The band: measured or padded

The measured-band method uses your snug underbust as the band, rounded to the nearest supported even band. Our +4 comparison first rounds both measurements to whole inches, with half inches rounded upward. It adds 4 inches to an even rounded underbust or 5 to an odd one (Wikipedia, "Bra size"), then subtracts the padded band from the rounded bust. Differences below 1 inch are labeled AA. That floor matters: the displayed cup-volume index can be smaller, equal or larger than the measured-band result. This is our declared comparison, not calculator.net's differently implemented +4 row. White and Scurr (Ergonomics, 2012) measured 45 women and found the traditional method overestimated band size and underestimated cup size, and got worse as bands got bigger.

The rounding order

An odd underbust, say 33 in, sits between the 32 and 34 bands. Rounding the band up to 34 makes the band one inch longer than your ribcage, and one inch of band is worth half a cup (a band step of 2 in trades for one cup letter; that is what sister sizes are). So a 33 in underbust with a 37 in bust lands between 34C and 34D. A Bra That Fits prints exactly that, "34C/D". Our recorded calculator.net result was 34D: it rounded the band but kept the cup from the raw 4 in difference. Further synthetic checks on 13 October 2026 found that fractional differences were truncated, not rounded up. Our comparison helper models those recorded inch-input rules over the supported comparison range; it is not a claim to reproduce every case on that site. We show both letters and explain our rounding rule.

The letters after DD

Up to DD, UK and US cups share letters. After that the UK goes E, F, FF, G, GG, H and the US goes DDD, G, H, I, J (Wikipedia, and A Bra That Fits' own output). A UK 34E and a US 34DDD are the same size. Some US brands print E for DD and F for DDD, which is how a "34E" can mean two different cups. The converter handles all of these.

What the Bra Atlas calculator does

  • Converts centimeters to inches (÷ 2.54). Nothing is rounded before the end.
  • Band = underbust rounded to the nearest even inch; an exact odd number rounds up, as A Bra That Fits does.
  • Cup position = (bust − underbust) − (band − underbust) ÷ 2, rounded to the nearest half. A whole number is one letter; a half shows both letters.
  • Other countries' labels are the same band and cup, relabeled: EU band 70 = UK 32, France = EU + 15, Australia = UK − 22, Japan = EU band (see the international chart for the cup ladders).
  • Our +4 result rounds the measurements to whole inches, pads the band, then uses the rounded bust minus that padded band, with a minimum cup label of AA. It is shown in US letters for comparison, not as a recommendation to add inches to a band that fits.

These rules live in one TypeScript module. Tests compare its results with 18 recorded A Bra That Fits measurement pairs in UK, US, EU, French and Australian labels. Those tests set all underbust readings equal and all bust readings equal; they do not establish equivalence to its full six-measurement algorithm.

What a calculator can't tell you

A size from a tape is a starting point. Bra fit research checks the band, cups, underwire, center front and straps on the body; McGhee and Steele (2010) found that sizes from bra-sizing measurement systems differed significantly from professionally fitted sizes. If a bra in your calculated size fails a fit check, the fit fixes tell you which size to try next.

"80% of women wear the wrong size": where it comes from

The figure is on thousands of pages. We opened the studies behind it.

The studies, as publishedAbstracts read on 25 September 2026.
StudyWho was measuredResult
Wood, Cameron and Fitzgerald, 200830 women aged 18 to 26 with upper back pain80% in incorrectly sized bras (70% too small, 10% too large)
McGhee and Steele, 2010104 women in Australia, average age 4385% in ill-fitting bras
Greenbaum et al., 2003102 women referred for breast reduction surgeryAll wore the wrong size
White and Scurr, 201245 women in the UKThe +4 method oversized bands and undersized cups

Our read: the 80% comes from 30 young women with back pain. Small clinical groups consistently find most participants in the wrong size, which is a good reason to measure. It is not a measured share of all women, so we don't print it as one.

Quick answers

How do I find my bra size at home?

Measure your underbust snugly around the ribcage and your bust loosely at its fullest point, both with the tape level. Enter both readings without rounding. Our method rounds the band to the nearest supported even band, rounding an exact odd inch upward within the chart, and adjusts the cup for that change. It shows two letters when the result falls between cups.

Why do bra size calculators give different answers?

Three reasons: some still add 4 or 5 inches to the band (the +4 method), they round an odd underbust in different orders, and US and UK cup letters split after DD. On our 10 test measurements, calculator.net and A Bra That Fits disagreed on 2, both with an odd underbust.

Is the +4 method wrong?

It is a different sizing convention, not a universal fit rule. A 2012 study of 45 women in the UK (White and Scurr) found it overestimated band size and underestimated cup size compared with professional fitting criteria, more so at larger bands.

How accurate is a bra size calculator?

A calculator turns two tape measurements into a starting size, not a fitting. McGhee and Steele (2010) found that sizes from bra-sizing measurement systems differed significantly from professionally fitted sizes, and two well-known calculators disagreed on 2 of our 10 test measurements. Try the size, then use the sister-size table under your result to move the way the fit tells you.

What if my result is between two cup sizes?

Our calculation adjusts the cup by half a step for each inch of band rounding. An odd underbust can therefore produce a range, such as 34C/D from 33 in underbust and 37 in bust. Try both. Marks & Spencer and Elomi say the same about cups: spilling means a bigger cup, loose fabric or gaping means a smaller one.

Is a bust size calculator the same as a bra size calculator?

No. Your bust size is one of the two measurements. A bra size needs a band and a cup within a named sizing system, so a bust measurement alone cannot give a bra size. Enter your underbust too and this calculator does the rest.

Should I measure in inches or centimeters?

Either. Centimeters are converted to inches using 2.54 cm per inch. The measured-band method keeps the original readings for its rounding adjustment; our separate +4 comparison deliberately rounds to whole inches first.

Which size do I search for on Amazon?

Our Amazon searches use the US reference label, so a UK 34E becomes a search for 34DDD. Individual listings can use a different regional or brand label: check the product chart before choosing. These are searches, not products we picked.

Where to go from your size

Sources

Each source was opened and checked on the date shown, or on 25 September 2026. Where sources disagree, the page says so instead of picking one silently.

  1. A Bra That Fits calculator (community calculator of r/ABraThatFits): we submitted 18 measurement pairs in 6 systems on 25 September 2026; raw synthetic fixture outputs are linked from the methodology
  2. calculator.net, Bra Size Calculator: 10 measurement pairs run in a browser on 25 September 2026
  3. Wikipedia, "Bra size": UK and US cup ladders, the +4 method, EN 13402 and JIS cup steps
  4. White J, Scurr J. Evaluation of professional bra fitting criteria for bra selection and fitting in the UK. Ergonomics 2012;55(6):704-711: 45 women; the traditional method overestimated band and underestimated cup
  5. McGhee DE, Steele JR. Optimising breast support in female patients through correct bra fit. J Sci Med Sport 2010;13(6):568-572: 104 women in Australia; 85% in ill-fitting bras
  6. Wood K, Cameron M, Fitzgerald K. Breast size, bra fit and thoracic pain in young women. Chiropractic & Osteopathy 2008;16:1: 30 women aged 18 to 26; 80% in incorrectly sized bras
  7. Greenbaum AR et al. An investigation of the suitability of bra fit in women referred for reduction mammaplasty. Br J Plast Surg 2003;56(3):230-236: 102 women referred for breast reduction; all wore the wrong size
  8. Marks & Spencer, "How to Measure Bra Size": fit checks; sister sizing; a tape gives a rough starting point (opened 25 September 2026)
  9. Elomi, "Bra Fitting Guide": five checks: center front, underband, cups, straps, underwire (opened 29 September 2026)