Bra Size Calculator | NovaCalculator

Medical disclaimer: This calculator is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Results are general estimates and may not reflect your individual circumstances. Always consult a qualified healthcare professional before making decisions about your health.

Formula

Cup Size = Bust Measurement - Band Measurement

Measure the band snugly around the ribcage under the bust and round to an even number of inches; measure the bust loosely at its fullest point. The difference in inches sets the cup: under 1 inch is AA, 1 inch is A, 2 inches is B, and so on. Sister sizes keep the same cup volume by trading two inches of band for one cup letter. No sizing standard is binding on manufacturers, so treat any calculated size as a starting point to try on.

Worked Examples

Example 1: Standard Calculation

Problem:Band measure: 30 inches, Bust: 34 inches.

Solution:Band size = 30 (round to even) Difference = 34 - 30 = 4 inches 4 inches = D cup Size: 30D

Result:30D

Example 2: Sister Size Example

Problem:Wearing 34B but band feels loose.

Solution:Current: 34B Band loose → go down in band Sister size down: 32C (Same cup volume, tighter band) Try 32C for better support.

Result:Try 32C

Example 3: Metric Conversion

Problem:Band: 75 cm, Bust: 90 cm.

Solution:Convert to inches: Band: 75 ÷ 2.54 = 29.5 → rounds to 30 Bust: 90 ÷ 2.54 = 35.4 → rounds to 35 Difference = 35 - 30 = 5 inches 5 inches = DD (US) = E (UK/EU) EU band = 30 × 2.5 - 10 = 65 Size: 30DD (US) or 65E (EU)

Result:30DD / 65E

Frequently Asked Questions

How do I measure my bra size?

Measure band: around ribcage, directly under bust, snugly. Measure bust: around fullest part, loosely. The difference determines cup size. Wear an unpadded bra or no bra.

What are sister sizes?

Sister sizes have the same cup volume but different band sizes. 34C = 32D = 36B in cup volume. If band is too tight, try sister size up; if too loose, try sister size down.

Why doesn't my calculated size feel right?

Sizing varies by brand. Breast shape, spacing, and fullness affect fit beyond size. Try your calculated size plus sister sizes. Consider professional fitting for best results.

How often should I measure?

Measure every 6-12 months or after weight changes, pregnancy, or hormonal changes. Sizes can fluctuate throughout life and even during menstrual cycles.

What's the difference between US and UK sizes?

US and UK band sizes are the same (in inches). Cup progression differs after D: US uses DD, DDD, G while UK uses DD, E, F, FF, G. Always check brand's size chart.

How should a properly fitting bra feel?

Band: snug, parallel to floor, 2 fingers fit underneath. Cups: no spillage or gaping. Straps: supportive but not digging. Center: sits flat against sternum.

Why do I get different sizes at different stores?

There's no universal sizing standard. Each brand uses slightly different measurements. Always try on and check the brand's specific size guide.

What is band size?

Band size is the circumference of your ribcage just below the bust, measured in inches (US/UK) or centimeters (EU). It should be snug for support.

How is cup size determined?

Cup size = bust measurement - band measurement. Each inch of difference is roughly one cup size: 1"=A, 2"=B, 3"=C, 4"=D, 5"=DD, etc.

What if I'm between sizes?

Try both sizes. For band, round to nearest even number. For cup, try both adjacent sizes. Consider sister sizes. Fit varies by bra style (t-shirt, sports, etc.).

Background & Theory

Bra sizing uses a two-part system: band size (number) and cup size (letter). Together they determine fit and support.

Measuring:

Band Measurement:
Measure snugly around ribcage directly under bust. Round to nearest even number.

Bust Measurement:
Measure loosely around fullest part of bust, keeping tape parallel to floor.

Cup Size:
Difference between bust and band:

Difference	Cup
Under 1"	AA
1"	A
2"	B
3"	C
4"	D
5"	DD/E
6"	DDD/F
7"	G

Sister Sizes:
Same cup volume, different band:
32D = 34C = 36B = 30DD

International Conversions:

US	UK	EU
32	32	70
34	34	75
36	36	80
38	38	85

Fit Checklist:
✓ Band level, snug
✓ Cups smooth, no gaps
✓ Straps stay up
✓ Gore lies flat

History

The modern bra evolved from the corset in the early 20th century. Mary Phelps Jacob patented a bra design in 1914, made from handkerchiefs and ribbon. Cup sizing was introduced by S.H. Camp and Company in 1932 with letters A through D. Warner's added the modern band-cup system in 1935, revolutionizing fit. The post-war era brought standardization attempts, though sizing still varies by manufacturer. The 1970s saw sports bras emerge; the 1990s brought push-up styles. Fitting studies repeatedly find that many women wear a poorly fitting bra, though the figures quoted vary widely and come from small samples, so no single percentage is reliable. What is clear is that sizing is still not standardised between brands: extended band and cup ranges have become more common, but the same label can fit very differently from one label to the next. Trying the size on, plus its sister sizes, remains the practical test.

References

International Bra Size Conversion Charts