Bra Size Calculator
Find your US, UK and EU bra size from underbust and bust measurements, using the standard fitting method — plus your two sister sizes for a better fit.
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What this tool does
Find your US, UK and EU bra size from underbust and bust measurements, using the standard fitting method — plus your two sister sizes for a better fit. Measurements in inches over no padding, tape snug under the bust and level across the fullest point. Sizing is a starting point — brands and styles fit differently, and sister sizes often fit better than the measured size.
How to use the Bra Size Calculator
- Enter or select underbust measurement (inches).
- Enter or select bust measurement at fullest point (inches).
- Read the calculated result; change any measurement to compare alternatives.
Formula
Band = underbust rounded to the nearest even inch. Cup steps from (bust - band): 0=AA, 1=A, 2=B, 3=C, 4=D, 5=DD, 6=DDD (UK E), then G/H... Sister sizes trade one band step for one cup step at the same volume.
- underbust
- Underbust measurement (inches)
- bust
- Bust measurement at fullest point (inches)
Measurements in inches over no padding, tape snug under the bust and level across the fullest point. Sizing is a starting point — brands and styles fit differently, and sister sizes often fit better than the measured size.
Worked example
For bra size calculator, the following measurements illustrate the exact method: Underbust measurement (inches): 34; Bust measurement at fullest point (inches): 38.
Inputs
- Underbust measurement (inches)34
- Bust measurement at fullest point (inches)38
Result
- US bra size34D
- UK bra size34D
- EU bra size75D
- Band size (inches)34
- Cup difference (inches)4
- Sister size (looser band)36C
- Sister size (tighter band)32DD
Results explained
- US bra size
- US bra size from the formula above. Measurements in inches over no padding, tape snug under the bust and level across the fullest point. Sizing is a starting point — brands and styles fit differently, and sister sizes often fit better than the measured size.
- UK bra size
- UK bra size from the formula above. Measurements in inches over no padding, tape snug under the bust and level across the fullest point. Sizing is a starting point — brands and styles fit differently, and sister sizes often fit better than the measured size.
- EU bra size
- EU bra size from the formula above. Measurements in inches over no padding, tape snug under the bust and level across the fullest point. Sizing is a starting point — brands and styles fit differently, and sister sizes often fit better than the measured size.
- Band size (inches)
- Band size (inches) from the formula above. Measurements in inches over no padding, tape snug under the bust and level across the fullest point. Sizing is a starting point — brands and styles fit differently, and sister sizes often fit better than the measured size.
- Cup difference (inches)
- Cup difference (inches) from the formula above. Measurements in inches over no padding, tape snug under the bust and level across the fullest point. Sizing is a starting point — brands and styles fit differently, and sister sizes often fit better than the measured size.
- Sister size (looser band)
- Sister size (looser band) from the formula above. Measurements in inches over no padding, tape snug under the bust and level across the fullest point. Sizing is a starting point — brands and styles fit differently, and sister sizes often fit better than the measured size.
- Sister size (tighter band)
- Sister size (tighter band) from the formula above. Measurements in inches over no padding, tape snug under the bust and level across the fullest point. Sizing is a starting point — brands and styles fit differently, and sister sizes often fit better than the measured size.
Frequently asked questions
Measure underbust snugly just below the bust, and bust loosely at the fullest point, both in inches with the tape level. Band = underbust rounded to an even number; each inch of bust-over-band difference is one cup step (1=A, 2=B, 3=C, 4=D, 5=DD).
Sizes with the same cup volume on a different band: 34D, 36C and 32DD are sisters. If the band feels tight but cups fit, go up a band and down a cup letter; the calculator lists both sisters.
They agree through D, then diverge: US DD = UK DD, but US DDD is UK E, and US G is UK F. This calculator shows both so you can shop either system.
EU sizes use the band in centimetres (34 in = 75) with the same early cup letters, e.g. 75D. The calculator converts the band and cup for you.
The method assumes standard proportions and unpadded measurements; breast shape, style (plunge vs balconette) and brand grading all change fit. Use the result and its sisters as the three sizes to try first.