The Bra Size Calculator turns underbust and bust measurements in inches into an estimated US band and cup, then lists sister sizes and approximate UK and EU labels. Measure snugly under the bust and at the fullest part of the bust, enter both figures, and read the size as a starting point for trying garments, not as a guarantee that every brand will fit the same way.
Bra sizing is measurement arithmetic plus brand variation. Two makers can cut the same printed size differently. This page stays practical: how to measure, how band and cup are derived, how sister sizes keep cup volume when the band changes, and how regional labels diverge. It does not rank bodies or treat size as a health score.
Calculate your bra size
US bra size pairs a band number with a cup letter. The band comes from the underbust measurement rounded to the nearest even inch. The cup comes from how many inches the bust exceeds that band, using roughly one inch of difference per cup step on the chart stored in the health reference.
Enter underbust (band) and bust (cup) in inches. The Bra Size Calculator returns an estimated US size such as 32DD, the numeric band, the cup letter, the inch difference used, sister sizes, and approximate UK and EU label hints. Units on this tool are inches for the measurement method described here.
The result is a fitting starting point for general information. Fabric stretch, brand blocks and personal comfort preferences still decide which garment feels right in the fitting room.
Measure your band and bust correctly
Band measurement is taken snugly under the bust, level around the torso, on bare skin or a thin unlined bra. Breathe normally; do not cinch to an uncomfortable extreme. Round that reading to the nearest even number for the US band method this page uses.
Bust measurement is taken at the fullest part of the bust, keeping the tape level and comfortable rather than tight. Wear the style of bra (or none) that matches how the finished garment will be worn if possible, because shape changes the tape reading.
Measure twice and average if the tape slips. A twisted tape or a high rear and low front reading will skew cup difference more than band. Soft measuring tapes meant for sewing beat rigid rulers for torso curves.
Calculate band and cup from measurements
Take underbust 32 inches and bust 37 inches. This is the worked fixture for the page. 1. Set the band. Underbust 32 is already even, so band = 32 2. Find the difference. Bust − band = 37 − 32 = 5 inches
3. Map difference to cup using the reference steps.
| Cup | Approx. difference (inches) |
|---|---|
| AA | 0.5 |
| A | 1 |
| B | 2 |
| C | 3 |
| D | 4 |
| DD | 5 |
| DDD | 6 |
A 5-inch difference maps to DD, so the estimated US size is 32DD.
If underbust were 31.4 inches, the method would round to the nearest even band (30 or 32 depending on exact rounding); enter careful measurements so the band step reflects the body rather than tape noise.
What this does not tell you: whether a particular brand's 32DD will feel firm or loose, or whether a wireless style needs a different sister size. It tells you the chart size implied by those two inches readings.
Find your sister sizes
Sister sizes keep similar cup volume while moving the band. Going down one even band and up one cup letter (or up one band and down one cup) is the usual sister move. For 32DD, the sister pair in range includes 30DDD (band down, cup up) and 34D (band up, cup down).
Sister sizing helps when the cup volume feels right but the band rides up, digs in or stretches out. A tighter band with a larger letter can hold the same cup volume more securely; a looser band with a smaller letter can ease pressure while preserving volume.
Not every sister exists at the extremes of the chart. When the calculator lists fewer sisters, the neighbouring cup step fell outside the AA to DDD set stored for this tool. Brands that cut past DDD will have their own extended charts.
Try the calculated size and one sister when possible. Comfort and a level band under load beat loyalty to a single printed label.
Convert between US, UK and EU sizing
US, UK and EU systems label the same body differently. This tool's approximate conversions keep the US band and cup as the source, then show UK and EU hint labels. Cups often align for common letters; UK charts frequently map DDD to E.
EU bands are commonly shown near underbust centimetres (inches × 2.54, rounded), with cup letters that do not always match US letters one-for-one (for example DD may appear as E on some EU charts).
For the 32DD fixture, approximate labels include UK 32DD and an EU-style band near 81 with a chart-dependent cup letter. Treat those as hints for shopping filters, then confirm on the brand's own size chart before ordering.
Regional conversion cannot erase brand grade rules. A UK 32DD from one maker still needs a try-on or a flexible return policy when buying online.
Check fit after you calculate
A calculated size is a starting label. In a well-fitting bra the band sits level around the torso and provides most of the support, the cups contain tissue without overflow or empty wrinkling at the top, and straps adjust without digging into the shoulders to hold everything up.
If the band rides up at the back, try a firmer band sister (smaller band, larger cup letter) before assuming the cup is wrong.
Wire shape, stretch fabrics and unlined styles change how the same printed size feels. Soft cup and sports bras may need a different sister than a structured underwire. Re-measure when weight, training or hormonal cycles change torso soft tissue enough that previous bras feel different, rather than forcing an old label.
Online orders benefit from reading the brand's own chart beside this estimate. When the brand chart and this calculator disagree by a full cup or band step, prefer the brand chart for that purchase and keep the sister-size idea for troubleshooting fit once the garment arrives.
Frequently asked questions
How do I calculate bra size from measurements?
Measure underbust snugly and bust at the fullest point. Round underbust to the nearest even inch for the US band. Subtract band from bust; about one inch of difference per cup letter maps A, B, C, D, DD and DDD on this chart (AA at about 0.5 inch).
What size is underbust 32 and bust 37?
Band 32 with a 5-inch difference maps to DD on this reference chart, so the estimated US size is 32DD. Sister sizes include 30DDD and 34D.
What are sister sizes?
Sister sizes pair a smaller band with a larger cup letter, or a larger band with a smaller cup letter, to keep similar cup volume. They help when volume fits but the band does not.
Why do brands fit differently in the same size?
Patterns, fabrics and stretch differ. Printed size is a starting label. Fit in motion (walking, reaching) is the real test.
How do US, UK and EU sizes differ?
Bands and cup letters are not universal. EU bands often track underbust centimetres; UK cup letters sometimes rename steps past DD. Use the calculator's hints, then check the retailer's chart.
Should the underbust tape be tight?
Snug and level, not painful. An overly tight underbust reading forces a smaller band and can inflate the cup letter when bust is held constant.
Is bra size a health measurement?
No. This page is a clothing measurement converter. It does not assess health, posture diagnosis or body composition.
What if my difference falls between cup letters?
The tool picks the nearest cup step on its chart. When between sizes, try the neighbouring cup and a sister band in person if possible.
Do I need a professional fitting?
A trained fitter can help when measurements are unclear, when sizes fall outside common charts, or when pain and marks persist across several brands. Many people still start with a home measurement and a sister-size try-on. Neither replaces the other completely; use whichever gets a comfortable, supportive result faster.
Can I measure in centimetres?
This page's method and fixture use inches because the US cup chart here is defined in inch steps. Convert centimetres to inches (divide by 2.54) before entry, or use a tape with inch markings. EU shopping labels may still show centimetre bands after the US size is calculated.
Summary
The Bra Size Calculator estimates a US band and cup from underbust and bust inches, using even-band rounding and about one inch of difference per cup letter on the AA to DDD chart. Underbust 32 with bust 37 yields 32DD, with sister sizes 30DDD and 34D and approximate UK and EU labels for shopping filters.
Sister sizing preserves cup volume when the band changes. Brand cut still varies, so treat the result as a starting measurement for trying garments, not a fit guarantee.