Bra AtlasBra sizing, measured and sourced

How to measure bra size, step by step

Measuring yourself can feel a bit awkward. It gets easier once the tape is in your hands. Two readings are all this needs: a snug one under the bust and a loose one around it. Keep both unrounded for the calculator. The leaning check further down is a separate reading, not a rule to always choose the largest number.

Already measured? Use the calculator

Find a quiet minute and a soft tape. Nothing here is stored, and nobody sees these numbers but you.

  1. 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

    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, pull it snug, breathe out and read it. Record the reading without rounding; the calculator handles band rounding.

    Keep the tape snug and level. Read after breathing out.

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

    Bust

    While standing, wrap the tape around the fullest part of the bust, level and resting on the skin without pressing in. If you also take a leaning reading, keep it separate rather than automatically replacing the standing reading.

    Loose, resting on the skin without pressing in. See the leaning check.

The cup

Enter both unrounded readings in the calculator. It uses the bust-to-underbust difference and adjusts for band rounding. When the underbust is an even whole inch and no band rounding is needed, differences of 1, 2, 3, 4 and 5 in correspond to A, B, C, D and DD. With an odd 33 in underbust and 37 in bust, our method gives 34C/D.

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

Four mistakes that throw the result off

None of these mean you measured wrong. They are the four things that nudge a reading off, so it is worth a glance before you trust the number.

  1. Breathing in for the underbust

    A snug underbust is measured after you breathe out, not while holding your breath in.

  2. Pulling the bust tape tight

    The bust tape sits loose, resting on the skin without pressing in. A tight tape can reduce the reading and lead to a smaller estimate.

  3. Letting the tape ride up at the back

    Check a mirror or a photo: both tapes should stay level all the way round.

  4. Measuring over a padded or molded bra

    Padding and molding can affect the reading. Measure over an unlined bra or none at all.

Why the leaning check matters

Side-view illustration of a woman with warm brown skin leaning forward at the hips, with a loose tape around the fullest part of the bust.
Lean forward at the hips, keeping the tape loose at the fullest point.

A Bra That Fits asks for three bust measurements: standing, leaning forward and lying down, alongside three underbust readings. Its measuring illustration shows the leaning reading with the body bent forward at the hips and the tape loose around the bust. Those are separate inputs; there is no instruction on its form to replace them with the largest number.

Our calculator is a two-input estimate, not a reproduction of that six-input method. Keep your standing and leaning readings separate. If you want to use A Bra That Fits' method, enter all the readings into its calculator. You can compare estimates here using each bust reading, but a larger calculated cup is not automatically the better fit. Use the fit check after trying a bra.

Once you have both numbers, the calculator shows the size on both the measured-band method and the older +4 method, in UK, US, EU, French, Australian and Japanese labels, and explains why two calculators can give different answers from the same tape.

Measuring while pregnant or nursing

The same two readings, taken more often.

The steps above don't change; how often you take them does. Bravissimo's maternity guide says size can change throughout pregnancy and suggests getting fitted regularly. NCT, the UK parenting charity, adds that bra fit is not the same as bra size, citing research that fit matters more than the tape, so pair each new reading with the fit check.

  • When. NCT says a bra bought from around 28 weeks should still fit after the birth, though some people need a larger cup in the early months. For a nursing bra, Bravissimo's nursing guide suggests waiting until about 36 to 37 weeks, and Kindred Bravely names 35 to 36 weeks.
  • Room to adjust. NCT says a pregnancy bra should be able to adapt and stretch, and Bravissimo points to stretch fabrics and extra hooks for that. For a bra bought during pregnancy, Bravissimo suggests the tightest hook so there is room to loosen it as the body changes; JoJo Maman Bébé says one bought just before the birth should fit on the loosest, so it can be tightened afterwards. Kindred Bravely includes a free extender with every hook-and-eye bra.
  • While nursing. Kindred Bravely suggests measuring at midday, before a feed, while the breasts are full.
  • Afterwards. Bravissimo recommends regular fittings while breastfeeding and says size can change again after weaning. Measure again then, rather than going back to an old size.

Measuring for a first bra

For the adult helping, and for the person who will wear it.

The same tape works for a first bra, measured alone or with someone helping. Marks & Spencer's first-bra guide suggests raising the subject gently and letting them lead the way. Many first bras and crop tops are not sold in band and cup at all but in letter sizes (XS to XL) or by band alone, and sizes vary by brand. Nike and Fruit of the Loom size their girls' bras from the ribcage reading; the bust reading comes in once a style has cups.

One letter, three chartsSize S on each brand's own girls' bra chart, read 8 October 2026.
ChartTape it readsIts size SBand or cup listed
NikeUnderbust26 to 27 in (66 to 69 cm)None: sizes run XS to XL
Fruit of the LoomRibcage, directly under the chest25 to 26 in (64 to 66 cm)Band 30; many styles have no cup size
Cat & Jack (Target)Fullest part of the chest25 to 26 in (64 to 66 cm)30A

Same letter, different tape: Fruit of the Loom and Cat & Jack both put S at 25 to 26 in with a 30 band, but one measures the ribcage and the other the fullest part of the chest. Nike's S starts an inch higher. Use the chart for the exact bra you are buying; a size doesn't carry from one brand to the next.

  • Between sizes. Nike's teen guide says to go for the bigger one.
  • No tape? Nike and Target both suggest a string or shoelace, then a ruler.
  • Measure again often. Bleuet's first-bra sizing guide suggests every three to six months, or sooner if a bra starts to feel uncomfortable.
  • Moving on. Nike suggests women's sizes once measurements reach the top of its girls' chart or cups are wanted; from there the calculator gives a band and cup.

Quick answers

What do I need to measure my bra size?

A soft tape measure and a mirror. No app or special equipment is needed.

Should I measure over a bra or without one?

An unlined, unpadded bra or no bra at all. Padding or molding can affect the reading.

Why do I need to lean forward to measure my bust?

A Bra That Fits asks for separate standing, leaning and lying bust readings, as well as three underbust readings. Do not assume its calculation always uses the largest. Keep those readings separate; if you want that six-measurement method, enter all of them into its calculator.

How often should I measure again?

Weight change, pregnancy, surgery and simply time can all move your size. Measure again if a bra that used to fit starts riding up, digging in, gaping or spilling.

Can I measure my bra size while pregnant?

Yes, with the same two measurements, taken more often. Bravissimo suggests regular fittings through pregnancy and waiting until about 36 to 37 weeks to buy a nursing bra. Once you are nursing, Kindred Bravely suggests measuring at midday, before a feed.

How do I measure for a first bra?

Take the same snug ribcage measurement and match it to the chart for the exact bra you are buying. Many first bras are sold in XS to XL or by band alone, and each brand maps its sizes differently: Nike's girls' S starts at a 26 inch ribcage, Fruit of the Loom's at 25 inches.

Other tools

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. Victoria's Secret UK, "Measure Your Bra Size": band = snug underbust rounded to the nearest even number; fit fixes; sister table (opened 25 September 2026)
  3. Wikipedia, "Bra size": UK and US cup ladders, the +4 method, EN 13402 and JIS cup steps
  4. 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
  5. Bravissimo, "Maternity Bra Guide": size can change throughout pregnancy, so get fitted regularly; fasten a new bra on the tightest hook; stretch fabrics and more hooks for flexibility (opened 8 October 2026)
  6. Bravissimo, "Nursing Bra Fitting & Sizing Guide": buy a nursing bra at around 36 to 37 weeks; get fitted regularly while breastfeeding; size can change again after weaning (opened 8 October 2026)
  7. NCT, "Maternity bras and nursing bras: what you need to know" (last reviewed 17 September 2026): a bra bought from around 28 weeks should still fit after the birth; it should adapt and stretch; fit is not the same as size (opened 8 October 2026)
  8. Kindred Bravely, "Fitting Guide": buy bras to nurse in at around 35 to 36 weeks; measure for a nursing bra at midday, before a feed; a free extender with every hook-and-eye bra (opened 8 October 2026)
  9. JoJo Maman Bébé US, "Maternity Bra Guide & Bra Size Calculator": a bra bought just before the birth should fit on the loosest setting, to be tightened afterwards (opened 8 October 2026)
  10. Marks & Spencer US, "How To Choose The Best First Bra": broach the topic gently and let them lead the way (opened 8 October 2026)
  11. Nike, "Teen Bra Guide": girls' bras XS to XL by underbust, S = 26 to 27 in; between sizes, go for the bigger one; women's sizes at the top of the girls' chart (opened 8 October 2026)
  12. Fruit of the Loom, "Girls' Size Guide", bras: ribcage 25 or 26 in = band 30, size S; many girls' styles have no cup size (opened 8 October 2026)
  13. Target, Cat & Jack "Girls Bra" size chart: XS to XL, with S to XL listed as 30A to 36A, read from the fullest part of the chest; S = 25 to 26 in (63.5 to 66.0 cm) (opened 8 October 2026)
  14. Bleuet, "First Bra Sizing Made Simple" (updated 17 July 2026): remeasure every three to six months, or sooner if a bra causes discomfort (opened 8 October 2026)