Bra Atlas

How to find your bra size, gently and step by step

All you need is a soft tape and two minutes. Pop in two measurements and we'll show you your size, why another calculator might have said something different, and what to try if a bra still doesn't feel right.

Units
A line drawing of a dress form in a bra that follows your measurements
Drawn for 32 in and 37 in: about a 32DD. Move the sliders and it follows you.

Everything stays on your device. Nothing you type is sent anywhere.

Your fitting card appears here: your size in six countries' labels, its sister sizes, and where to go next.

By Rai Ansar · Sizes computed by the Bra Atlas engine, sources checked · How this page was made

  1. Underbust: snug around the ribcage, right under the bust, tape level. Read it after you breathe out.
  2. Bust: loose around the fullest point, tape level, without squashing. Lean forward slightly if the tissue is soft.

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

How to measure

Two minutes, a soft tape and a mirror. Wear an unlined bra or none, and keep the tape comfortable rather than tight.

Standing: underbust and bust tape positions A line drawing of a dress form wearing a bra. A snug, level tape sits just under the bust along the band line; a looser, level tape sits around the fullest point. bustloose underbustsnug, level
Standing: tape snug under the bust, then loose at the fullest point.
Leaning: the bust measured bent forward A simple side-view line drawing of a person bent forward at the hips with the back level and arms relaxed. A loose tape loops around the fullest point of the bust. bust, loose,at the fullest point
Leaning forward: a truer fullest point if the tissue is soft or wide-set.
  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. If the tissue is soft or wide-set, measuring while leaning forward at 90 degrees gives a truer fullest point; A Bra That Fits asks for standing, leaning and lying bust measurements for this reason.
  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.

What we measured

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

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 the traditional US method.
UnderbustBustBra AtlasA Bra That Fitscalculator.net+4 method (US)
28 in30 in28B28B28B32 (below AA)
30 in34 in30D30D30D34AA
32 in35 in32C32C32C36 (below AA)
33 in37 in34C/D34C/D34D38 (below AA)
34 in38 in34D34D34D38AA
36 in41 in36DD36DD36DD40A
38 in44 in38E38E38E42B
29 in33 in30C/D30C/D30D34 (below AA)
40 in46 in40E40E40E44B
42 in48 in42E42E42E46B

Highlighted rows are where calculator.net disagrees: both have an odd underbust (33 in and 29 in). Raw outputs, including 8 more pairs in all six systems, are published in our repository's docs/sources folder.

Brands disagree too

The same tape, 34 in underbust and 38 in bust, through three brands' own tools on 26 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 even inch. The older +4 method adds 4 inches to an even underbust and 5 to an odd one (Wikipedia, "Bra size"), and then takes the cup from the bust minus that padded band. A padded band shrinks the difference, so the cup comes out smaller: on every even fixture above, the +4 size holds exactly two cup volumes less. 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". calculator.net prints 34D: it rounds the band but takes the cup from the raw 4 in difference, before rounding. Neither page explains the choice. We show both letters and tell you why.

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 centimetres 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, relabelled: EU band 70 = UK 32, France = EU + 15, Australia = UK − 22, Japan = EU band (see the international chart for the cup ladders).
  • The +4 result uses the rule above and US letters, for comparison only.

These rules are one TypeScript module with more than 130 tests that pin it to the recorded outputs of both calculators, including every A Bra That Fits answer for 18 measurement pairs in five systems.

What a calculator can't tell you

A size from a tape is a starting point. Bra fit research checks the band, cups, underwire, centre 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. Round the underbust to the nearest even inch for the band. Each inch of difference between bust and underbust is one cup letter: 1 is A, 2 is B, 3 is C, 4 is D, 5 is DD.

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 was built for older, less stretchy bands. 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.

Where to go from your size

Sources

Each source was opened and checked 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 output is in our repository
  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