Bra Measurement Calculator
By Mohit Patel, Marketing Specialist, Tailor Size Guide
Enter two measurements, your underbust and your bust, and this bra size calculator gives your size in US, UK, EU, French and Australian sizing, plus your sister sizes. Below it is a full bra measurement chart and the method behind it.
The short answer
Band = your snug underbust, rounded to the nearest even inch. Cup = bust minus band: 1" = A, 2" = B, 3" = C, 4" = D, 5" = DD, 6" = DDD/F (US) or E (UK). Example: underbust 31.5", bust 36" → band 32, difference 4" → 32D.
Calculate your bra size
Enter both measurements to see your size.
How to measure for a bra (3 steps)
- Prepare. Use a soft fabric tape. Wear a non-padded, non-minimiser bra, or no bra. Stand straight in front of a mirror so you can check the tape stays level across your back.
- Underbust (band). Wrap the tape around your ribcage directly under the breasts. Pull it snug, so it is firm but you can breathe, and read it after a normal exhale. Round to the nearest even inch. This number carries most of the support: in the research below, the band was the part of the bra most often wrong.
- Bust (cup). Wrap the tape around the fullest part of the bust, usually across the nipples, level at the back. Keep it loose enough not to compress tissue. If your breasts are soft or sit low, also measure leaning forward at 90 degrees and use the larger of the two readings.
Want photos for each step? See our guide on how to measure bra band and cup size. If one breast is larger, measure and fit to the larger side; our guide to fitting a bra when your breasts are different sizes covers the details.
Bra measurement chart: underbust to band size
Find your snug underbust measurement in the first two columns to read your band in each sizing system.
| Underbust (in) | Underbust (cm) | US / UK band | EU band | FR band | AU band |
|---|---|---|---|---|---|
| 26–27" | 66–69 cm | 26 | 60 | 75 | 4 |
| 28–29" | 71–74 cm | 28 | 65 | 80 | 6 |
| 30–31" | 76–79 cm | 30 | 65–70 | 80–85 | 8 |
| 32–33" | 81–84 cm | 32 | 70 | 85 | 10 |
| 34–35" | 86–89 cm | 34 | 75 | 90 | 12 |
| 36–37" | 91–94 cm | 36 | 80 | 95 | 14 |
| 38–39" | 97–99 cm | 38 | 85 | 100 | 16 |
| 40–41" | 102–104 cm | 40 | 90 | 105 | 18 |
| 42–43" | 107–109 cm | 42 | 95 | 110 | 20 |
| 44–45" | 112–114 cm | 44 | 100 | 115 | 22 |
| 46–47" | 117–119 cm | 46 | 105 | 120 | 24 |
An odd underbust such as 31" sits between bands 30 and 32. Try both and keep the one that stays level without digging in.
Bra measurement chart: bust difference to cup size
Subtract your band size from your bust measurement. Each step is one cup.
| Bust − band (in) | Bust − band (cm) | US cup | UK cup | EU cup |
|---|---|---|---|---|
| Under 1" | Under 2.5 cm | AA | AA | AA |
| 1" | 2.5 cm | A | A | A |
| 2" | 5.1 cm | B | B | B |
| 3" | 7.6 cm | C | C | C |
| 4" | 10.2 cm | D | D | D |
| 5" | 12.7 cm | DD | DD | E |
| 6" | 15.2 cm | DDD/F | E | F |
| 7" | 17.8 cm | G | F | G |
| 8" | 20.3 cm | H | FF | H |
| 9" | 22.9 cm | I | G | I |
| 10" | 25.4 cm | J | GG | J |
| 11" | 27.9 cm | K | H | K |
| 12" | 30.5 cm | L | HH | L |
EU sizing measures bust minus underbust in 2 cm steps under EN 13402; this table aligns it to the inch method, which agrees within one cup. For full band-by-cup grids, see the bra size chart.
Why this calculator does not add 4 inches
Many older guides tell you to add 4 or 5 inches to your underbust to get your band. That rule comes from bras built with rigid, non-stretch bands. Modern bands stretch, so the extra inches produce a band that rides up the back, which shifts the weight onto the shoulder straps.
The research agrees. White and Scurr (2012) compared traditional tape-measure methods with professional fit criteria and found the traditional methods tended to give a band that was too large and a cup that was too small. McGhee and Steele (2010) found most women they assessed were wearing a poorly fitting bra, with the band the most frequent problem. That pattern, band too big and cup too small, is exactly what the "+4" rule produces.
If a brand's own chart still uses "+4", follow that brand's chart for that brand. The calculator shows the "+4" result alongside yours so you can translate.
Sister sizes
Cup volume depends on the band. A 32D, a 34C and a 36B hold roughly the same volume. Move down a band and up a cup, or up a band and down a cup. Read more in what is a sister size.
| Sister down (tighter band) | Your size | Sister up (looser band) |
|---|---|---|
| 32D | 34C | 36B |
| 32DD | 34D | 36C |
| 34D | 36C | 38B |
| 30DD | 32D | 34C |
| 36DD | 38D | 40C |
Check the fit after you order
A calculator gives a starting size. These five checks confirm it.
- Band: level all the way round, fastened on the loosest hook, and you can slide two fingers under it but not more.
- Centre gore: the middle piece between the cups sits flat against your sternum.
- Cups: no gap at the top edge and no spilling over the top or sides.
- Underwire: sits behind the breast tissue at the sides, not on it.
- Straps: carry only a small share of the weight; they should not dig in or leave marks.
Fit varies by style and activity. For workouts, use the sports bra measuring guide; for pregnancy, see bras during pregnancy and nursing.
Frequently asked questions
How do I calculate my bra size?
Measure your underbust snugly, directly under the breasts, and round it to the nearest even number: that is your band. Then measure your bust loosely across the fullest point. Subtract the band from the bust. Every 1 inch of difference is one cup size: 1" = A, 2" = B, 3" = C, 4" = D, 5" = DD.
Should I add 4 inches to my underbust measurement?
Not with modern bras. The "+4" rule dates from when bands were made of non-stretch fabric. Research by White and Scurr (2012) found that traditional measuring methods tend to overestimate band size and underestimate cup size compared with professional fit criteria. Most UK and EU brands now size from the underbust measurement directly.
Why does the calculator show two sizes?
If your underbust falls on an odd number, such as 31 inches, you sit between two bands. The calculator shows the tighter band first and the looser band as an alternative. Try both: the right band sits level and stays put when you lift your arms.
What is a sister size?
A sister size holds the same cup volume on a different band. Go down one band and up one cup (34C to 32D), or up one band and down one cup (34C to 36B). Use it when the cups fit but the band is too loose or too tight.
How common is wearing the wrong bra size?
Very common. In a study of 100 women referred for breast reduction surgery, Greenbaum and colleagues (2003) found most were wearing an incorrectly sized bra. McGhee and Steele (2010) reported that the large majority of women they assessed wore a poorly fitting bra. Calculators give a starting size; a try-on confirms it.
Are US, UK and EU bra sizes the same?
Band numbers in inches are the same in the US and UK, but cup letters split after D: the UK uses DD, E, F, FF, while US brands usually use DD, DDD/F, G, H. EU sizing uses centimetres: a UK 34 band is an EU 75, and EU cups step in 2 cm increments.
How often should I remeasure?
Every 6 to 12 months, and after weight change of a few kilograms, pregnancy, breastfeeding, starting a new exercise routine, or menopause. Breast tissue volume and ribcage measurements both change over time.
Sources
- White J, Scurr J. Evaluation of professional bra fitting criteria for bra selection and fitting in the UK. Ergonomics, 2012.Compared traditional tape-measure methods with professional fit criteria; traditional methods tended to give a band that was too large and a cup that was too small.
- McGhee DE, Steele JR. Optimising breast support in female patients through correct bra fit. A cross-sectional study. Journal of Science and Medicine in Sport, 2010.Assessed bra fit against professional criteria and found most participants wore a poorly fitting bra; the band was the most common problem.
- Greenbaum AR, Heslop T, Morris J, Dunn KW. An investigation of the suitability of bra fit in women referred for reduction mammaplasty. British Journal of Plastic Surgery, 2003.Found that most women in the study were wearing a bra with a band too large and a cup too small.
- EN 13402 (European standard for clothing size designation).Defines bra sizing by underbust girth in centimetres with cup letters by bust–underbust difference, the basis of EU bra sizes.
This calculator gives a starting size, not a medical assessment. Sizes differ between brands; always compare with the brand's own chart.
Sell lingerie on Shopify?
Put this bra size calculator on your own product pages. Tailor Size Guide adds per-product bra charts and a fit recommender, so shoppers order the right size first time.