The short version: measure snugly around your ribcage under your breasts and round to the nearest even number. That is your band. Measure around the fullest part of your bust and subtract the band. Each inch of difference is one cup: 1 inch is an A, 2 a B, 3 a C, 4 a D, 5 a DD, 6 an E.
Before you start
- Use a soft fabric or fibreglass tape. Old cloth tapes stretch with age. If yours is decades old, check it against a ruler.
- Measure on bare skin, or in a thin unpadded bra. Padding inflates the bust figure. A sports bra or minimiser squashes it.
- Stand in front of a mirror. Turn side-on to check the tape is level at the back, where it most often slips down.
- Stand normally. Shoulders relaxed, breathing as usual, arms down once the tape is in place.
Step 1: measure your underbust
Wrap the tape around your ribcage directly beneath your breasts, where a bra band sits. Check in the mirror that it runs level all the way round. Breathe out normally and pull the tape snug: firm against the skin, without digging in.
Tape position and tension are covered in detail in how to measure your underbust.
Write the number down exactly, including any half inch. If you get 30¾, write 30¾. Rounding comes later.
Step 2: measure your bust
Move the tape up to the fullest part of your bust, usually across the nipples. Keep it level at the back. This time the tape should only rest on the skin. If it presses a groove into the breast tissue, it is too tight and will undersize your cup.
The leaning check
Stand with your feet apart and bend forward at the hips until your back is flat, like a table top. Let your breasts hang freely and measure around the fullest part again.
For firm or self-supporting breasts the two figures will be close. For softer tissue, or breasts that sit lower without a bra, the leaning figure is often an inch or two bigger. That happens because the standing measurement misses tissue that a bra would lift and contain. If the gap is more than an inch, use the average of the two as your bust figure.
All three bust positions, and how to combine them, are in how to measure your bust.
Step 3: find your band
Round your underbust to the nearest even number. That is your band size. Add nothing to it.
| Underbust | Band | Underbust | Band |
|---|---|---|---|
| 27–29 in (69–74 cm) | 28 | 35–37 in (89–94 cm) | 36 |
| 29–31 in (74–79 cm) | 30 | 37–39 in (94–99 cm) | 38 |
| 31–33 in (79–84 cm) | 32 | 39–41 in (99–104 cm) | 40 |
| 33–35 in (84–89 cm) | 34 | 41–43 in (104–109 cm) | 42 |
If you land on an odd number you are between two bands. Neither is wrong. As a guide, go down if you have soft tissue around your ribs or like a firm fit, and go up if your ribcage is bony or firm bands irritate you. Then let the bra decide: how tight a band should be explains what to feel for.
Step 4: work out your cup
Subtract your band size from your bust measurement. Count one cup for every inch.
| Difference | UK cup | Difference | UK cup |
|---|---|---|---|
| Under 1 in | AA | 6 in | E |
| 1 in | A | 7 in | F |
| 2 in | B | 8 in | FF |
| 3 in | C | 9 in | G |
| 4 in | D | 10 in | GG |
| 5 in | DD | 11 in | H |
The UK sequence has double letters that catch people out. DD comes before E, and FF comes before G. The full ladder is in UK cup sizes in order, and every band and cup combination is laid out in the UK bra size chart.
Worked examples
A straightforward one
Underbust 34 inches, bust 38 inches. The band is 34. The difference is 4 inches, which is a D. Starting size: 34D.
With a leaning measurement
Underbust 30½ inches. Standing bust 35 inches, leaning bust 37 inches. The band rounds to 30. The two bust figures are two inches apart, so use the average, 36. The difference is 6 inches. Starting size: 30E. The standing figure on its own would have given 30DD, a cup too small.
In centimetres
Underbust 86 cm, bust 102 cm. Divide by 2.54 to get 33.9 and 40.2 inches. The band is 34. The difference is about 6 inches. Starting size: 34E.
If you would sooner skip the arithmetic, the bra size calculator does it in either unit.
Mistakes that change the result
- Adding inches to the underbust. Older size guides add four or five inches before choosing a band. That produces a band that is too loose and a cup that is too small. See why the +4 method is wrong.
- A tape that dips at the back. A sloping tape travels further around you and can add an inch or more.
- Holding your breath or pulling the tape painfully tight on the underbust. Snug on a normal out-breath is the target.
- Pulling the bust tape tight. It should not compress anything.
- Measuring over a padded or moulded bra. You will measure the bra as well as yourself.
- Measuring once. Take each measurement twice. If the two differ, take a third.
If the result surprises you
It is very common to measure into a smaller band and a larger cup letter than you have been wearing. Someone in a 36C often measures as a 32DD or 32E. That can look alarming, but the cup volume is similar. A 36C, 34D and 32DD all hold about the same amount. What has changed is that the band now does its job. The idea is explained in what sister sizes are.
A measured size is still a first estimate. Tape measures cannot see breast shape, and brands cut their bras differently. The confirmation comes when you try the bra on: put it on, scoop and swoop, and go through how a bra should fit.
Measuring at particular times of life
The method is the same for a first bra, though the fitting needs a lighter touch: see our first bra fitting guide. During pregnancy and breastfeeding your measurements keep moving, so use the nursing bra calculator, which builds in the right allowance for your stage. For exercise, the sports bra calculator starts from the size you find here.
Want more precision?
The two-measurement method is quick and good enough for most people. If you are between sizes, or your results never seem to match what fits, a fuller method that takes three underbust and three bust measurements can help. We explain it in the ABraThatFits method, explained for UK sizes.
Frequently asked questions
What time of day should I measure?
Any time works, as long as you are consistent. If your breasts change noticeably through your cycle, measure at the point when they are at their fullest, because a bra that fits then will still be wearable for the rest of the month.
Can I measure myself without help?
Yes. Stand side-on to a mirror so you can see whether the tape is level across your back. That is the one thing a second person would otherwise check for you.
What if I do not have a tape measure?
Wrap a piece of non-stretchy string or ribbon around you, mark where it meets, and lay it flat against a ruler or a steel tape. It is slower but gives the same numbers.
How often should I re-measure?
About once a year, and after anything that changes your body: pregnancy, breastfeeding, a noticeable change in weight, menopause, or starting or stopping hormonal contraception.
Not measured recently? It takes two minutes.
Open the bra size calculator →