Fit & Sizing

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Bra Size Calculator: US, UK, EU & AU/NZ Conversions

Find your bra size from band and bust. Converts to US, UK, EU, AU/NZ. Sister sizes and fit guide.

Bra Size Calculator

Units

Band Size

Under-bust measurement, snug and straight. Rounded to nearest even number.

Bust Size

Fullest part, tape parallel to floor.

Show Legacy (+4) Sizing

Your Size (US)

34C

Global Sizes

Standard US

34C

Standard UK

34C

Standard EU

85C

FR/BE/ES

EU +15

100C

AUNZ

Dress size

12C

UK Dress

Dress size

12C

EU band in cm; US/UK in inches. FR/BE/ES = EU + 15. UK uses double letters (DD, FF, GG).

Sister Sizes

32D Down band, up cup36B Up band, down cup

Information Hub

How to Measure

The tape must be parallel to the floor. Use a mirror to ensure the back isn't sagging—this is the #1 cause of incorrect measurements.

Band

Tape straight across your back, under the bust. Snug but not digging in.

Bust

Over the fullest part (nipples), tape parallel to the floor.

The Sister Size Secret

Same cup volume, different band. Going up a band and down a cup (or vice versa) can find a more comfortable fit.

Example: 34C, 36B, and 32D hold the same cup volume. If your size feels off, try a sister size. Your calculated sister sizes appear in the results card.

The 80% Problem

~80% of people wear the wrong bra size. Proper fit: the band provides 80% of the support and the straps only 20%. If the straps are doing the work, the band is too big.

Common signs of a bad fit:

Straps digging into shoulders
Band sliding up your back
Spillage or gaping at the cups
Red marks that linger after removing

If any of these sound familiar, remeasure and try this calculator. Sizing varies by brand—use this as a starting point.

Why is my size different in-store?

Some traditional brands add 4 inches to your band measurement (the "Plus 4" method). Our calculator uses modern industry standards for better support.

If a brand feels too tight, try your Sister Size instead—same cup volume, different band.

Shape Matters More Than Size

Measurements only account for volume. Factors like breast "projection" (full on bottom vs. full on top) will affect how a cup fits.

If you have gapping at the top but the wires fit, try a balcony or demi-style cup.

Reference Tables

Band size mappings across regions (XXS to 5XL). FR/BE/ES = EU + 15.

Size	FR/BE/ES	EU (cm)	US/UK (in)	AU/NZ
XXS	75	60	28	6
XS	80	65	30	8
S	85	70	32	10
M	90	75	34	12
L	95	80	36	14
XL	100	85	38	16
2XL	105	90	40	18
3XL	110	95	42	20
4XL	115	100	44	22
5XL	120	105	46	24

Cup	US/UK (in)	EU (cm)
AA	<1"	<2 cm
A	1"	2 cm
B	2"	4 cm
C	3"	6 cm
D	4"	8 cm
DD	5"	10 cm
DDD/E	6"	12 cm
F	7"	14 cm
G	8"	16 cm
H	9"	18 cm
I	10"	20 cm

How Bra Sizing Actually Works

Bra sizing comes down to two numbers and a simple formula. Get the math right, then use sister sizes and regional conversions when a brand runs small or your exact size sells out.

The Cup Formula

Modern sizing uses your actual measurements. Cup size comes from the difference:

\text{Cup} = \text{Bust} - \text{Band}

. In US/UK (inches), each inch equals one cup: 1" = A, 2" = B, 3" = C, and so on. In EU (EN 13402), each

2\,\text{cm}

equals one cup. Band rounds to the nearest even number.

Legacy Plus 4 Sizing

Some traditional brands use

\text{Legacy band} = \text{Measured band} + 4

(if measured band is even) or +5 (if odd). Our calculator uses modern standards—better support and fit. If a brand feels too tight in your calculated size, try your sister size instead of switching to legacy.

When to Try a Different Style

Measurements give volume, not shape. Full on top vs. full on bottom changes how a cup fits. Gapping at the top with wires that sit right? Balcony or demi cups often work better than full-coverage.

Bra Size Calculator: US, UK, EU & AU/NZ Conversions

Find your bra size from band and bust measurements. Converts to US, UK, EU (EN 13402), FR/BE/ES, and AU/NZ. Sister sizes, fit tips, shape guide. Free bra size chart and calculator.

How to Use This Calculator

Enter Your Measurements

Band:

Under-bust, snug, tape straight and parallel to the floor. We round to the nearest even number.
Bust:

Over the fullest part, tape parallel to the floor. Use inches or centimeters—toggle converts automatically.

Regional Size Differences

US vs UK cups

UK double letters:

UK uses DD, E, F, FF, G, GG where US often jumps to DDD, G. Same cup volume, different labels.
EU band:

EU band is in centimeters (70, 75, 80…). FR/BE/ES adds 15 to EU (e.g. EU 75 → FR 90).
AU/NZ:

Uses dress size convention for band (e.g. US 34 band ≈ AU 12).

Bra Size Calculator FAQ

? How do I measure my band size?

Snug tape under your bust, straight across your back and parallel to the floor. Round to the nearest even number—industry standard. If you land on an odd number, try both the size above and below; band fit varies by brand.

? How do I measure my bust size?

Over the fullest part (usually nipple level), tape parallel to the floor. Wear a non-padded bra or none. Keep the tape loose enough that it doesn't compress your chest.

? Why is bust size larger than band size?

Bust wraps the fullest part of your chest; band sits under the breasts. The difference drives cup size. In inches: 1" = A, 2" = B, 3" = C. In cm (EN 13402):

2\,\text{cm}

per cup. So

\text{Cup} = \text{Bust} - \text{Band}

in both systems.

? What are sister sizes?

Same cup volume, different band. 34C, 36B, and 32D hold the same. Band too tight? Go up a band, down a cup. Cups gaping? Try down a band, up a cup.

? Do sizes vary by brand?

Yes. Bra sizing isn't standardized. Use our calculator as a starting point, then try on in person. UK uses DD, E, F, FF where US often uses DD, DDD, G—our Global Sizes grid handles the conversion.

? What does the AA cup fit tip mean?

When bust − band is under 1 inch, an AA may fit better. Many stores skip AA/AAA. Look for brands that carry smaller cups, or try bralettes and wireless styles.

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Mathematical Reference Note

Calculation Logic: This tool uses standard mathematical algorithms. While we strive for accuracy, errors in logic or user input can result in incorrect data.

Verification: Results should be cross-checked if used for important academic, professional, or personal calculations.

Standard Terms: This tool is provided free of charge and as-is. CalcRegistry provides no warranty regarding the accuracy or fitness of these results for your specific needs.

Size	FR/BE/ES	EU (cm)	US/UK (in)	AU/NZ
XXS	75	60	28	6
XS	80	65	30	8
S	85	70	32	10
M	90	75	34	12
L	95	80	36	14
XL	100	85	38	16
2XL	105	90	40	18
3XL	110	95	42	20
4XL	115	100	44	22
5XL	120	105	46	24

Size	FR/BE/ES	EU (cm)	US/UK (in)	AU/NZ
XXS	75	60	28	6
XS	80	65	30	8
S	85	70	32	10
M	90	75	34	12
L	95	80	36	14
XL	100	85	38	16
2XL	105	90	40	18
3XL	110	95	42	20
4XL	115	100	44	22
5XL	120	105	46	24

Size	FR/BE/ES	EU (cm)	US/UK (in)	AU/NZ
XXS	75	60	28	6
XS	80	65	30	8
S	85	70	32	10
M	90	75	34	12
L	95	80	36	14
XL	100	85	38	16
2XL	105	90	40	18
3XL	110	95	42	20
4XL	115	100	44	22
5XL	120	105	46	24