Bra Size Calculator
What you need
You only need:
- Underbust measurement: Measure firmly around your rib cage, directly underneath your breasts.
- Bust measurement: Measure around the fullest part of your breasts without pulling the tape tightly.
For the most accurate result, use a soft measuring tape and measure in inches or centimeters.
How to calculate your bra size
- Measure your underbust.
- Determine your band size according to the sizing system used by the brand.
- Measure your bust at its fullest point.
- Calculate the difference between your bust and band measurements.
- Match that difference to a cup-size chart.
- Try the calculated size and assess the fit.
Important: Bra-size conversion is not universal. US, UK, EU, and other sizing systems use different band and cup conventions.
Bra Size Measurement Chart
A common starting point for US/UK-style sizing is to compare your bust and band measurements:
| Bust-to-band difference | Approximate cup size |
|---|---|
| 1 inch | A |
| 2 inches | B |
| 3 inches | C |
| 4 inches | D |
| 5 inches | DD/E |
| 6 inches | DDD/F |
| 7 inches | G |
| 8 inches | H |
This chart is a general guide. Some brands use different cup progressions, particularly for larger cup sizes.
How to Measure Your Bra Size Correctly
1. Measure your underbust
Stand naturally and wrap the measuring tape around your torso immediately below your breasts. Keep the tape level all the way around your body.
The tape should be snug but not painfully tight.
Record the measurement.
2. Measure your bust
Wrap the tape around the fullest part of your breasts. Keep the tape horizontal and avoid compressing breast tissue.
Record this measurement separately.
3. Determine your cup size
The cup size is generally based on the difference between the band measurement and bust measurement.
For example, if your band measurement is approximately 34 inches and your bust measurement is approximately 38 inches, the four-inch difference corresponds roughly to a D cup, giving an estimated size of 34D in a common US/UK sizing system.
How Should a Correctly Fitting Bra Feel?
Your calculated size is only a starting point. A properly fitting bra should generally have:
| Bra area | What to look for |
|---|---|
| Band | Snug and level around your body |
| Cups | Breast tissue contained without spilling or gaping |
| Center gore | Lies comfortably against the breastbone when the style is designed to do so |
| Straps | Secure without digging into your shoulders |
| Underwire | Surrounds the breast without sitting on breast tissue |
| Back band | Does not ride significantly upward |
The band provides most of the bra’s support, so it should feel secure without being uncomfortably tight.
What If Your Bra Size Doesn't Fit?
If your cups fit but the band feels too loose or tight, you may need a sister size.
Sister sizes change the band and cup together while keeping approximately the same cup volume:
| If your size is | Try |
|---|---|
| 34C | 32D or 36B |
| 36D | 34DD or 38C |
| 38DD | 36DDD/F or 40D |
Sister sizing is useful for fine-tuning fit, but it does not mean every neighboring size will fit identically. Cup shape, wire width, bra construction, and brand sizing also matter.
Why Does the Same Bra Size Fit Differently?
Bra sizing is not completely standardized. Two bras labeled with the same size can fit differently because of:
- Different brand sizing systems
- US versus UK cup-size conventions
- Cup shape and depth
- Underwire width
- Stretch in the fabric
- Bra construction
- Breast shape and fullness
- Individual fit preferences
For this reason, a bra size calculator provides an estimate, not a definitive size.
Bra Size Conversion
When shopping internationally, check the brand’s own conversion chart rather than assuming that a US size directly corresponds to a UK or EU size.
| Sizing system | Example format |
|---|---|
| US | 34D |
| UK | 34D |
| EU | 75D |
| France | 90D |
| Australia | 12D |
The exact conversion becomes more complicated as cup sizes increase, so always use the manufacturer’s chart when available.
Frequently Asked Questions
What is a bra size calculator?
A bra size calculator estimates your bra size from your underbust and bust measurements. It typically uses the underbust measurement to determine the band size and the difference between bust and band measurements to estimate the cup size.
Should I measure my bra size with a bra on?
A thin, unpadded bra can make measuring easier, but heavily padded or push-up bras can distort the measurement. Measuring without a bra or while wearing a thin, unpadded bra is generally preferable.
Should the measuring tape be tight?
The underbust tape should be snug and level, while the bust measurement should be taken without compressing the breasts.
Is bra size based only on breast size?
No. Bra size combines a band measurement with a cup size. The cup letter by itself does not describe an absolute breast size because cup volume changes with the band size.
For example, a 32D and 38D do not have the same cup volume.
How often should I recalculate my bra size?
Re-measure whenever your body measurements change noticeably or your bras begin fitting differently. Weight changes, pregnancy, breastfeeding, aging, and other body changes can affect bra fit.
The Bottom Line
A bra size calculator is a useful starting point for finding your bra size. Measure your underbust and fullest bust accurately, calculate your approximate band and cup size, and then verify the result by checking how the bra actually fits.
For the best result, use the calculator together with the specific sizing chart provided by the bra manufacturer, because sizing and fit can vary significantly between brands and styles.