How to Measure Your Bra Size
Two measurements, one soft tape, about a minute. This is the exact technique professional fitters use, with diagrams you can follow, a calculator that updates as you go, and the mistakes that throw the number off. No tape at hand? Four ways to measure without one.
Enter your measurements as you take them
Wondering how your result compares to others? See what the "average" figures actually mean.
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The two measurements, one at a time
Underbust: your band
Wrap the tape directly under the bust, where the band of a bra sits. Pull it snug (firm against the ribcage, the way a well-fitting band feels) and level all the way round. Exhale normally and read it.
- Tape flat, no twists, directly under the breast root
- Level front to back: check in a mirror
- Snug: it should feel like a firm band, not a loose necklace
- Round to the nearest whole inch; odd numbers round up to the even band
Bust: your cup
Wrap the tape around the fullest point of the bust, usually at nipple level, over a thin unpadded bra or bare. Keep it level and let it rest without compressing tissue: light contact, no squeeze.
- Fullest point, not the top of the breast
- Level: the back of the tape at the same height as the front
- Touching, not squeezing: compression costs you a cup
- Soft tissue? Lean forward 45° so it fills its natural shape
Subtract: your size
Bust minus band is your cup, one letter per inch: 1″ = A, 2″ = B, 3″ = C, 4″ = D, 5″ = DD, 6″ = DDD. Your band is the underbust number. The equation below follows the calculator above.
- The cup is a difference, not a bust number
- Same letter on a bigger band = bigger cup
- Odd underbust? Try both neighbouring bands with sister sizes
Why two people measuring the same body get different sizes
Two things move the number more than anything else: how tight you pull the tape, and whether it stays level. Try both.
Level all the way round: the shortest path around the ribcage, and the true band measurement.
Snug measure vs. the old +4 rule
Older charts told you to add four or five inches to your underbust to get a band size. That rule dates from an era of non-stretch fabrics and it inflates band sizes today: it's the reason so many people wear a band that's too loose and a cup that's too small.
The modern snug-measure method uses the underbust measurement directly. Modern bands stretch; a 34 band is designed to fit a 33–34-inch ribcage snugly, on the loosest hook when new.
Key takeaway: if a calculator adds inches to your underbust, it's using the outdated method. Ours doesn't, and every size page tells you what your +4 size really is.
Same body: the old rule pushes you into a loose band and a cup three letters too small.
Five bodies, five sizes
The same two steps applied to different measurements. Notice how the cup letter follows the difference, not the bust number.
| Underbust (snug) | Band | Bust (fullest) | Difference | Size | Sister sizes |
|---|---|---|---|---|---|
| 28½″ · 72 cm | 28 | 32″ · 81 cm | 4″ | 28D | 30C |
| 31″ · 79 cm | 32 | 34″ · 86 cm | 2″ | 32B | 30C · 34A |
| 33″ · 84 cm | 34 | 37″ · 94 cm | 3″ | 34C | 32D · 36B |
| 35½″ · 90 cm | 36 | 42″ · 107 cm | 6″ | 36DDD | 34G · 38DD |
| 39″ · 99 cm | 40 | 44″ · 112 cm | 4″ | 40D | 38DD · 42C |
Odd underbust readings round to the nearest even band; when it's a coin toss, try both bands and use sister sizes to keep the cup volume constant.
The things fitters check that charts leave out
Most people have one breast slightly larger. Measure the bust with the tape over the fuller side's fullest point and fit the cup to the larger breast: a removable pad or a slightly deeper cup style evens the smaller side. Never fit to the smaller breast.
If tissue sits low when unsupported, take the bust measurement leaning forward at about 45° so the breast hangs into its natural fullest shape, or over a thin unpadded bra that lifts it. Standing measurements on soft tissue read one to two cups small.
Measuring in centimeters works identically: switch the calculator above to cm, or use the centimeter calculator and cm lookups. Each cup step is about 2.5 cm of difference. EU labels are then band × 2.5 − 10 from the US band, not your raw centimeter reading.
Fit a new bra on the loosest hook. Bands lose tension with wear and washing; over six to nine months you move inward to the middle and tightest hooks. A band that only fits on the tightest hook when new is already too big.
Four things that throw the number off
A slack tape adds an inch or two and inflates the band. Pull it snug: you should feel it against the ribs. Try the tension demo above.
The tape must stay level. A dip of even an inch changes the reading. Use a mirror or a second person.
Push-up and padded styles add material at the bust line. Measure over a thin unpadded bra or bare.
The bust tape should touch, not squeeze. Compressing tissue shrinks the difference and gives a cup that's too small.
Measuring: answered
How do I measure my bra size at home?
Measure snugly under the bust for the band, then around the fullest point for the bust. Subtract band from bust; each inch of difference is one cup letter (1″ = A, 2″ = B, 3″ = C, 4″ = D, 5″ = DD, 6″ = DDD).
Should I add inches to my underbust measurement?
No. The +4/+5 rule is outdated and produces bands that are too loose. Modern bands stretch and are designed to match your snug underbust measurement directly.
Should the tape be tight or loose?
Snug for the underbust: firm against the ribcage like a well-fitting band. Light contact for the bust: touching without compressing tissue. Two inches of slack on the underbust turns a 34C into a 36B.
What if my underbust is an odd number?
Bands come in even numbers. If you measure 33, try both 32 and 34 and let the band decide: it should be snug on the loosest hook when new. Then use sister sizes to keep the cup volume right.
Do I measure with a bra on or off?
Either works if the bra is thin and unpadded and lifts you into a natural position. Never measure over padding or push-up.
How do I measure my bra size in cm?
Exactly the same way: snug underbust, fullest bust. Switch the calculator on this page to centimeters. Each cup step is about 2.5 cm of difference; the EU label is then US band × 2.5 − 10.
How often should I re-measure?
Whenever your body changes (weight, pregnancy, hormonal shifts) and at least once a year. Bra bands also stretch with wear, so a size that fit six months ago may not now.
Can I measure my bra size without a tape measure?
Use a piece of string or a phone charging cable, mark it, and lay it against a ruler. Keep the same tension rules: snug for the underbust, light for the bust.
Opens HauteFlair’s own hub page; use your measured size there. HauteFlair is owned by the same company as Brasize.ai; that relationship never changes the sizing math, charts, or fit advice on this page. How this site makes money.
Got your two numbers?
The calculator on this page already has your size, or run the full calculator for sister sizes and eight-system conversions.
Calculate My Bra Size →