A bra that rides up, straps that dig into your shoulders, or cups that wrinkle or spill over: in most cases, the problem is caused by choosing the wrong size. The good news is that it only takes a few minutes and a measuring tape to fix it.
In this guide, you will learn how to measure your bust circumference accurately, understand the difference between bust and underbust circumference, and convert your measurements into a bra size.
Why is it important to measure your bust circumference correctly?
According to several lingerie studies, around 8 out of 10 women wear a bra that does not fit them. The right size makes all the difference:
-
Better support without excessive compression
-
Greater comfort every day, at work and during sports
-
A more harmonious silhouette under clothing
-
Less tension in the back, shoulders, and neck
Knowing how to measure your bust circumference is also useful for choosing a bodysuit, a fitted dress, or shapewear, whose sizes are based on the same measurements.
What you need
Before you start calculating your bust circumference, prepare:
-
A flexible measuring tape (for sewing, not DIY)
-
An unpadded bra, or a thin bra without thick underwires (or no bra)
-
A mirror to check that the measuring tape stays perfectly horizontal
-
A pen and paper to record your results
Tip: measure yourself at the end of the day and avoid the period just before your period, when your breasts may be fuller.
How to calculate your bust circumference in 4 steps
You need to take two measurements because bra size combines the underbust circumference (the back size) and the bust circumference (which determines the cup size).
Step 1: measure your underbust circumference
Place the measuring tape just below the bust, where the bra band rests, around your torso. The tape should be perfectly horizontal, flat against the skin, and snug without being tight. Breathe normally and note the measurement in centimeters.
Step 2: measure your bust circumference
Wrap the tape around your bust at its fullest point, generally at nipple level. Keep it horizontal, without compressing your bust or letting it hang loose. This is the measurement referred to when talking about bust size.
Step 3: Calculate the difference
Subtract your underbust measurement from your bust measurement. This difference determines your cup depth.
Example: bust measurement 96 cm − underbust measurement 80 cm = 16 cm difference.
Step 4: Find your bra size
Round your underbust measurement to the nearest multiple of 5: this will be your band size. Then enter the calculated difference in the chart.
|
Difference (cm) |
Cup |
|
12-13 |
A |
|
14-15 |
B |
|
16-17 |
C |
|
18-19 |
D |
|
20-21 |
E |
|
22-23 |
F |
In our example, the underbust measurement is 80 cm and the difference is 16 cm: the size is therefore 80C.
This chart corresponds to the French sizing system. British, American, and Italian systems work differently. So always check the brand's bra size guide.
How to measure your bust without a tape measure
Don't have a tape measure on hand? You can use a piece of string or a non-stretch ribbon. Wrap it around your bust as described above, mark where the two ends meet, then measure the length with a ruler. It's a little less convenient, but the result remains reliable as long as the string does not stretch.
Mistakes to avoid when measuring your bust
Even when following the method, a few mistakes can skew the result.
-
Pulling the tape too tight: You will get a measurement that is too small and a band size that is too tight.
-
Letting the tape tilt: If it drops at the back, the measurement will be inaccurate. Check in the mirror that it remains parallel to the floor.
-
Measuring yourself while wearing a heavily padded bra: Padding adds volume and distorts the bust measurement.
-
Leaning forward or slouching: Stand straight with your arms at your sides.
-
Relying only on your old size: Your body changes with weight, pregnancy, breastfeeding, age, or exercise. Take your measurements again at least once a year.
How to check that the size is right
The calculation provides a starting point, but trying it on confirms the result. A well-fitting bra shows these signs:
-
The band is horizontal, neither riding up at the back nor too tight. You should be able to slide two fingers underneath.
-
The cups fully contain the breasts, without wrinkles or spillage.
-
The center gore lies flat against the sternum.
-
The straps do not dig into the shoulders: the band provides most of the support, around 80%.
-
The underwires surround the breasts without compressing them or pressing against the ribs.
If the band rides up, try a smaller band size with a larger cup (the “sister size”: 85C becomes 80D, for example). The cup volume remains equivalent.
For those also looking for support and shaping under clothing, discover our selection of shaping bodysuits.
Bust measurements vary depending on the brand and style
The same measurement does not always correspond to the same size from one brand to another. The cut, fabric stretch or style (triangle, balconette, push-up, bralette) affects the fit. To avoid surprises:
-
Check the size guide specific to each brand
-
Read customer reviews about the fit (small, large, loose)
-
Take two sizes with you when trying items on, whenever possible
In summary
To calculate your bust measurement, follow the 4-step method: measure your underbust, measure your bust at its fullest point, calculate the difference, then convert it into a size using the chart. Allow five minutes, a tape measure and a little precision to avoid the most common mistakes.
These measurements will be useful for your bras as well as any fitted clothing, and recalculating them each year ensures that you always wear the right size.
FAQ: Calculating your bust measurement
How do you calculate your bust measurement?
To calculate your bust measurement, wrap a soft tape measure around your bust at its fullest point, keeping it horizontal and without pulling it tight. Then measure your underbust directly beneath your breasts. The difference between the two measurements determines your cup size.
How do you calculate bust measurement for a bra?
Measure your underbust and round it to the nearest multiple of 5: this is the band size. Measure your bust, then calculate the difference. A difference of 12-13 cm corresponds to an A cup, 14-15 cm to a B, 16-17 cm to a C, and 18-19 cm to a D.
What is the difference between bust and underbust measurements?
The bust measurement is taken at the fullest part of the breasts. The underbust measurement is taken just below the breasts, where the bra band rests. The latter determines the band size, and the difference between the two determines the cup size.
How can I measure my bust by myself, without help?
It is entirely possible. Stand in front of a mirror to check that the tape remains horizontal, stand up straight with your arms at your sides, and read the measurement on the tape. If the tape slips, hold it in place with one hand at the small of your back.
How often should I take my measurements again?
At least once a year, and after any significant change: weight fluctuation, pregnancy, breastfeeding, menopause, or a change in sports activity. Your breasts change throughout your life.
Should I measure myself with or without a bra?
The most reliable approach is to measure yourself without a bra, or while wearing a thin, unpadded, non-push-up style. A heavily padded bra adds volume and distorts the bust measurement.
What is the most common bra size in France?
Sizes 85B, 90B, and 85C are among the best-selling, but there is no real “average size”: every body shape is different. Only your measurements matter.
Can you calculate your bust measurement without a measuring tape?
Yes, with a piece of string or a non-stretchable ribbon. Wrap it around your bust, mark where the ends meet, then measure the length of the string with a rigid ruler.
What should I do if my measurements fall between two sizes?
Choose the larger size for more comfort, or try the “sister size” (one band size down and one cup size up, or the reverse) depending on whether the band is too loose or too tight. Trying it on is still the best judge.