How do I measure my bra size at home?

You need a soft measuring tape. Band size: measure snugly around your torso, directly under your bust (at the bra band line). Round to the nearest even number — if odd, round up by 1. Bust size: measure loosely around the fullest part of your bust. Lean forward slightly to allow the bust to hang naturally for the most accurate measurement.

What does sister sizing mean?

Sister sizes are bras with the same cup volume but different band sizes. The cup volume stays constant while you go up or down a band size: as band increases by 2, cup letter decreases by one (and vice versa). 32D = 34C = 36B = 38A all have the same cup volume. If the band feels right but cups don't, stay in your band size. If the band is the issue, sister size.

How do I know if my bra fits correctly?

The band should sit horizontally across your back (not riding up), feel snug on the loosest hook (tightest hooks are for when the band stretches with wear), and you should be able to fit two fingers underneath comfortably. The center gore (between cups) should lie flat against your sternum. Cups should contain the full breast without gaping or spillage. Straps should provide 20% of support — if you're relying on them heavily, the band is too loose.

Why is the +4 inch method outdated?

Older measurement methods added 4–5 inches to the underbust measurement to get band size — because bra fabrics were less stretchy and needed extra sizing. Modern bras use highly elastic fabrics and should fit to your actual measurement (rounded to nearest even number). The +4 method systematically produces too-large bands and too-small cups, which explains why many women measured 'the old way' are wearing the wrong size.

❤️Health

What Bra Size Should You Be Wearing? Bra Size Calculator

What bra size should you be wearing?

What This Does

Research suggests that the majority of women are wearing the wrong bra size — most commonly a band that's too large and a cup that's too small. The consequences are more than just comfort: an ill-fitting bra provides inadequate support, can cause back and shoulder pain, affect posture, and make clothing fit poorly. Finding your correct size requires measuring two dimensions and understanding how band and cup interact. Bra sizing is based on two measurements: the band size (your torso circumference just below the bust, rounded to the nearest even number) and the cup size (the difference between your full bust circumference and your band size). In the US system, each inch of difference corresponds to a cup letter: 1" = A, 2" = B, 3" = C, 4" = D, 5" = DD/E, and so on. The critical concept most people miss is sister sizing: cup volume stays constant as band size changes. A 34C has the same cup volume as 36B or 32D. If your 34C fits in the cups but the band is too loose, try 32D — same cup volume, smaller band. This sister size relationship opens up a much wider range of options in store. This calculator computes your US bra size, provides your full sister size chart, and converts to UK, EU, French, and Australian sizing.

When Should You Use This?

→Finding your correct bra size when you suspect you're wearing the wrong size
→Checking your size after significant weight change, pregnancy, or breastfeeding
→Understanding how to convert between US, UK, and European bra sizes
→Finding sister sizes when your exact size isn't available in store
→Troubleshooting fit issues — band too tight, cups gaping, straps falling

Example Scenario

Jennifer measures 33" below the bust (rounds to 34" band) and 37" at fullest point. Difference: 37 - 34 = 3 inches → C cup. Size: 34C. Sister sizes: 32D (smaller band, same cups), 36B (larger band, same cups). UK equivalent: 34C (same). EU equivalent: 75C. She now knows to try 32D if she finds the 34 band rides up.

How to Measure Correctly

📏

Underbust

Measure snugly directly under your bust at the bra band line. Exhale fully. Round to the nearest half inch.

📐

Full Bust

Measure loosely around the fullest part of your bust. Keep the tape parallel to the floor. Lean slightly forward for accuracy.

Your Measurements

Unit:

Underbust (in)

Full Bust (in)

About the Bra Size Calculator

Finding the right bra size is more nuanced than most people realize. Studies consistently show that a large majority of people who wear bras are wearing the wrong size — typically with a band that's too large and a cup that's too small. This calculator uses the standard method of measuring underbust and full bust to calculate your band size and cup letter, then converts to all major international sizing systems.

The two key measurements are your underbust (directly under your bust, snug) and your full bust (around the fullest part). Your band size is determined by rounding your underbust to the nearest even number. Your cup size is determined by the difference between your full bust and your band size — each inch of difference corresponds to one cup letter.

Sister sizes are an important concept that most fitting guides skip. A 34C, 32D, and 36B all contain the same cup volume — only the band size changes. Understanding sister sizes makes it easier to find a good fit when your exact size is unavailable, and can help you fine-tune fit when you're between sizes.

How Bra Sizing Works

The US system uses even numbers for band sizes (28 through 50+) and letters for cup sizes (AA, A, B, C, D, DD, DDD/F, G and beyond). The band number comes from your underbust measurement rounded to the nearest even inch. The cup letter comes from the difference between your full bust and your band size: a 1" difference = A cup, 2" = B, 3" = C, 4" = D, 5" = DD, and so on. European sizing converts the band to centimeters, while UK sizing uses a different sequence of cup letters at larger sizes.

Example Calculation

Say your underbust is 33" and your full bust is 37". Your band size rounds to 34 (nearest even number above 33). The difference between full bust (37) and band (34) is 3 inches, which corresponds to a C cup. Your US size is 34C. Sister sizes are 32D (same volume, smaller band) and 36B (same volume, larger band). International equivalents would be UK 34C, EU 75C, FR 90C, and AU 12C.

Common Measuring Mistakes

Measuring the underbust too loosely — it should be snug, not tight
Holding your breath while measuring — exhale normally for an accurate band
Measuring the full bust while upright with a padded bra on — lean forward slightly and measure without a bra or in a non-padded one
Assuming the result is final — sizes vary significantly by brand, style, and fabric

Frequently Asked Questions

How do I convert my US bra size to UK or European sizing?

The band number stays the same between US and UK sizing — only the cup letters differ at larger sizes. For example, a US 34DD is a UK 34DD but a US 34DDD is a UK 34E. European sizing converts the band to centimeters using the formula (band - 2) × 2 + 62, so a 34 band becomes 70 EU. French sizing adds 15 to the EU band. This calculator performs all conversions automatically.

Why does my bra size feel different in different brands?

Bra sizing is not standardized across manufacturers. A 34C from Victoria's Secret may fit very differently from a 34C from Wacoal or ThirdLove. Different brands use different wire widths, cup shapes, and band elasticity. It's always recommended to try on bras or read detailed size guides for each specific brand before purchasing online.

What is a sister size and when should I use one?

Sister sizes are adjacent sizes that contain the same cup volume — just with a different band. For example, 34C, 32D, and 36B are all sister sizes. You'd use a sister size when your exact size is out of stock, when one measurement seems right but the other doesn't, or when you want a different fit feel (a tighter band for more support, for example). Going down a band size means going up a cup letter to maintain volume.

My bra band feels too tight but the cup fits fine. What should I do?

A snug band feeling is actually correct — the band should feel firm, not painful. The band provides about 80% of a bra's support. If it feels genuinely uncomfortable, check that you're wearing it on the loosest hook (bras are sized for the loosest hook when new). If that's still too tight, size up the band by one (e.g., 34 to 36) and down one cup (e.g., C to B) to maintain the same cup volume — this is using the sister size principle.

Does bra size change over time?

Yes, bra size can change due to weight fluctuations, hormonal changes, pregnancy, breastfeeding, aging, and even significant changes in exercise habits. It's recommended to re-measure every 6–12 months or any time you notice fit issues with bras that previously fit well. Most fitting experts suggest remeasuring after any 10+ pound weight change.

What does the fit confidence score mean?

The fit confidence score is an estimate of how reliable the calculated size is likely to be for an immediate good fit. High scores (80+) indicate your measurements produce a standard size with minimal rounding. Lower scores indicate your measurements fall into specialty sizing ranges, or there's significant rounding between your underbust and band size — meaning trying on a wider range of sister sizes will be especially important.

Results are estimates only and do not constitute medical advice. Consult a qualified healthcare professional before making health decisions.