How the Bra Size Calculator Works
A bra size has two parts: a number for the band, and a letter for the cup. The band tells how big the bra is around the body, and the cup tells how much room there is for the bust in relation to the band. The Bra Size Calculator finds both from two measurements that you take yourself.
How to measure
- Underbust: put a soft tape around your ribcage, just under the bust, level all the way round. Breathe out, and pull the tape firm, but not tight.
- Bust: put the tape around the fullest part of your bust, level at the back, and not tight. Stand straight, and do not press the bust.
It is easier to do it in front of a mirror, in a thin bra without much padding. You can measure in inches or in centimeters.
The steps
band = underbust made to the nearest even number (in inches) cup = bust - band, rounded to a whole inch, changed to a letter
A difference of 1 inch is an A cup, 2 inches is a B cup, 3 inches is a C cup, and 4 inches is a D cup. After that, the letters depend on the system. A difference of 0 or less is AA. Example: an underbust of 32 inches and a bust of 36 inches give a band of 32, a difference of 4 inches, and so a size of 32D.
How the band is found
| Underbust | Band |
|---|---|
| 27 to under 29 in (69 to 74 cm) | 28 |
| 29 to under 31 in (74 to 79 cm) | 30 |
| 31 to under 33 in (79 to 84 cm) | 32 |
| 33 to under 35 in (84 to 89 cm) | 34 |
| 35 to under 37 in (89 to 94 cm) | 36 |
| 37 to under 39 in (94 to 99 cm) | 38 |
| 39 to under 41 in (99 to 104 cm) | 40 |
Bands are made in even numbers. A measurement exactly half way between two bands (33 inches) goes up to the next one (34).
Cup letters
| Bust minus band | In centimeters | US letters | UK letters |
|---|---|---|---|
| 1 in | 2.5 cm | A | A |
| 2 in | 5.1 cm | B | B |
| 3 in | 7.6 cm | C | C |
| 4 in | 10.2 cm | D | D |
| 5 in | 12.7 cm | DD | DD |
| 6 in | 15.2 cm | DDD | E |
| 7 in | 17.8 cm | G | F |
| 8 in | 20.3 cm | H | FF |
| 9 in | 22.9 cm | I | G |
| 10 in | 25.4 cm | J | GG |
| 11 in | 27.9 cm | K | H |
The US and the UK use the same letters up to DD (5 inches), and after that they differ. In the US, the letter after DD is often DDD (or E), and in the UK it is E, then F, FF, G and so on. Some brands use other letters, so check the chart of your brand. Each block of the chart is 0.2 of an inch of extra volume in the cup:
1 in █████ A (US) 2 in ██████████ B (US) 3 in ███████████████ C (US) 4 in ████████████████████ D (US) 5 in █████████████████████████ DD (US) 6 in ██████████████████████████████ DDD (US) 7 in ███████████████████████████████████ G (US) 8 in ████████████████████████████████████████ H (US)
Sister sizes
Sister sizes are sizes with a similar cup volume, but a different band. When the band gets one size (2 inches) bigger, the cup letter goes one letter smaller, and the other way round. So 32D, 34C and 30DD hold about the same amount. They are useful when a bra fits well in the cup, but is too tight or too loose in the band. The chart shows a family of sister sizes. The gray bar is the band (over 20), and the colored bar is the cup:
30DD band ██████████ cup ████████████████████ 32D band ████████████ cup ████████████████ 34C band ██████████████ cup ████████████ 36B band ████████████████ cup ████████ 38A band ██████████████████ cup ████
The calculator shows the sister size with a looser band and the one with a tighter band next to your result.
The European band
In Europe, the band is often given as the underbust in centimeters, in steps of 5 (for example 70, 75, 80). The calculator shows this number too, from your underbust. Because of the way that the older systems were made, a conversion chart from a US size to a European size can be different from this number, and it depends on the brand. Use the chart of the brand that you are buying.
Signs of a good fit
- The band is firm and level, and does not ride up at the back. You can just fit two fingers under it.
- Most of the support comes from the band, and not from the straps.
- The bust fills the cups without spilling out or leaving a gap.
- The center of the bra lies flat against the chest.
Tips
- Measure again from time to time. Your size can change with weight, age, pregnancy and the time of the month.
- Try different sizes. Brands and styles fit in different ways, so the size on the label can vary by a band or a cup.
- Use the sister sizes if the band or the cup is not right.
What this calculator does not include
- The shape and the fullness of the bust, the width of the chest and the shoulders, and the type of bra (sports, nursing or others).
- Differences between brands.
- A professional fitting. If you can, ask a bra fitter, especially for large cup sizes. The calculator does not give a size for a difference of more than 11 inches (US letters) or 15 inches (UK letters).
This tool gives an estimate for general information. Sizes are different from brand to brand, so try the bra on before you buy.