In this direct-fit calculator, a 3-inch difference between your rounded band and full bust starts at a C cup. That letter is only part of a full bra size: the band still changes the cup's volume.
Cup difference tool
Cup Size Calculator
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Cup Size Chart
A cup letter corresponds to the difference between full bust and rounded band; your result highlights below. This quick chart is for comparing letters, not for replacing the band portion of your complete bra size.
AA<1 in · <2.5 cm
A1 in · 2.5 cm
B2 in · 5.1 cm
C3 in · 7.6 cm
D4 in · 10.2 cm
DD5 in · 12.7 cm
DDD/E6 in · 15.2 cm
G7 in · 17.8 cm
H8 in · 20.3 cm
Why Cup Letters Are Relative
A 32C and a 38C use the same letter but hold very different volumes because the band changes the cup’s scale. Cup letters are a ratio, not a standalone volume measurement, so always read the number and letter together when comparing bras.
| Size | Band | Difference | Volume comparison |
|---|---|---|---|
| 32C | 32 | ≈3 in | Smaller cup volume than 34C and 38C. |
| 34C | 34 | ≈3 in | A midpoint comparison. |
| 38C | 38 | ≈3 in | Substantially more cup volume than 32C. |
How Sister Sizes Change Cup Volume
To keep close cup volume, move down one band and up one cup, or up one band and down one cup. The letter changes because cup volume is tied to the band number.
| Size | Band feel | Why it relates to 34C | When to test |
|---|---|---|---|
| 32D | Firmer | Close cup volume to 34C. | A 34 band rides up or feels loose. |
| 34C | Baseline | Baseline cup volume. | The band is level and comfortable. |
| 36B | Looser | Close cup volume to 34C. | A 34 band is painfully tight, not simply new-bra snug. |
Cup Size Calculator FAQs
Your cup letter is useful for comparing differences, but it only becomes a complete size when paired with a band. These answers explain why labels that look alike can fit differently.
A cup letter alone does not describe a fixed size or volume. A 32C and a 38C use the same letter but hold different volumes because the band changes the scale. Fit, shape, and comfort are more useful than calling a cup small or large.
A stretched band, an older plus-four chart, and brand-specific cup grading can all make your old label differ from a new measurement. You may also be wearing a sister size. Check your current bra’s fit signs, then use the measurement result as a clear starting point for trying nearby options.
Yes. A cup letter is relative to the band, so 32C and 38C are not the same cup volume. The letter only tells you the difference pattern within a band. That is why two people can both wear C cups while needing very different bra sizes and cup shapes.
It depends on the sizing system. In US sizing, DD is generally the next step after D and DDD/E often follows it. In UK sizing, DD is followed by E. Always check the brand’s stated system before comparing labels, especially once cup letters move beyond DD.
Related Tools & Guides
Use a full-size tool for the band, or move to a visual comparison when you want to see how the letters relate. Each page uses the same direct-fit calculation.