US Bra Size Calculator

If you buy bras in the United States, you shop in US sizes — a system with its own quirks, from DDD cups to brands that quietly swap in an F where the DDD should be. This free US bra size calculator estimates your US bra size from two simple tape measurements: your underbust and your bust. It takes less than a minute, accepts inches or centimeters, and hands you a US size you can take straight to a size chart or a fitting room.

Here is how it works. Enter your underbust — measured snugly right under your bust — and your bust — measured around the fullest part. The calculator rounds your underbust to the nearest even inch to set your band size, then turns the difference between your bust and band into a US cup letter, where each inch of difference equals roughly one cup step. Use Simple mode for the quick two-measurement estimate, or switch to Advanced mode for a more refined result based on six measurements.

Your result is an estimate and a starting point, never a guarantee of fit. US brands do not all cut the same way, and the same cup letter can feel different between styles and manufacturers. Always check the brand's own size chart when you can — and if you ever shop UK or EU labels, remember their cup letters diverge from US letters above a DD.

Enter Your Measurements

Not sure how to measure? See how to measure your bra size.

How to Measure for a US Bra Size

You only need a soft measuring tape and about two minutes. Wear a thin, unpadded bra (or nothing at all) so the tape sits against your body, and stand in front of a mirror so you can keep the tape level.

  1. Measure your underbust. Wrap the tape snugly around your ribcage, directly under your bust where the band would sit. Keep it level all the way around, breathe normally, and write down the number.
  2. Measure your bust. Wrap the tape around the fullest part of your bust — usually across the nipples — keeping it level and firm but not tight. Write down the number.
  3. Enter both numbers above in inches or centimeters and press Calculate. Your US band comes from the underbust, your US cup from the difference between the two.

For the full step-by-step guide with photos-style walkthroughs and troubleshooting, see how to measure your bra size.

US Bra Size Chart

This chart lists common US bra sizes by band and cup. Band sizes are in inches; cups follow the US letter progression. Note that some US brands label the DDD cup as F instead — the two are treated as the same cup here. Scroll sideways on small screens.

BandABCDDDDDD (F)G
3030A30B30C30D30DD30DDD30G
3232A32B32C32D32DD32DDD32G
3434A34B34C34D34DD34DDD34G
3636A36B36C36D36DD36DDD36G
3838A38B38C38D38DD38DDD38G
4040A40B40C40D40DD40DDD40G
4242A42B42C42D42DD42DDD42G
4444A44B44C44D44DD44DDD44G

AA cups and cups above G exist in US sizing too, but the sizes above cover the most commonly stocked range. Cups above DDD continue as G, H, I, J in the US system.

How US Bra Sizing Works

US bra sizing has two parts: a band number and a cup letter. Both are inch-based.

Band sizes

The band number is your underbust measurement rounded to the nearest even inch — 30, 32, 34, 36 and so on. US bands are always even numbers. If your underbust measures 33 inches, for example, your band is 34; at 33.6 it rounds to 34 as well, while 32.4 rounds down to 32.

Cup sizes

The cup letter comes from the difference between your bust and your band, with roughly one inch per cup step: a 1-inch difference is an A, 2 inches a B, 3 inches a C, 4 inches a D, 5 inches a DD, 6 inches a DDD, and then G, H, I, J as the difference keeps growing. The full US cup progression used by this calculator is AA, A, B, C, D, DD, DDD, G, H, I, J.

The DDD question

The most confusing part of US sizing is the cup after DD. The traditional US label is DDD, but some US brands label this exact cup F instead (a habit borrowed from other systems). A few brands also use E as an equivalent of DD. Labelling varies by manufacturer, which is why this calculator sticks to the standard US letters: DD, then DDD, then G. When comparing brands, treat DDD and F as the same cup and check the brand's own chart.

A worked example

Say your underbust measures 33.5 inches and your bust measures 37 inches. The band rounds to 34. The difference is 3 inches, which is a C cup. Your estimated US size is 34C.

US to UK Bra Size Conversion

US and UK band numbers are identical — a 34 band is a 34 band in both systems. The cup letters, however, match only from AA through DD and then diverge. This table converts common US sizes to their closest UK equivalents at the same band, using a 34 band as the example:

US sizeUK sizeHow close is the match?
34A34ALetters match exactly
34B34BLetters match exactly
34C34CLetters match exactly
34D34DLetters match exactly
34DD34DDLetters match exactly
34DDD34EApproximate — closest UK cup
34G34FApproximate — closest UK cup
34H34FFApproximate — closest UK cup
34I34GApproximate — closest UK cup
34J34GGApproximate — closest UK cup

These conversions are approximations, not exact equivalents. No international standard forces brands to align, so a US 34G from one label and a UK 34F from another may still fit differently. Use the table as a starting point when crossing between US and UK brands, and always check the manufacturer's own chart. Our UK bra size calculator and the US, UK and EU size guide go deeper on the differences.

US Sister Sizes

Sister sizes are sizes that hold roughly the same cup volume on a different band. Go down a band and up a cup, or up a band and down a cup. For example, a US 34C has the sister sizes 32D (tighter band, same cup volume) and 36B (looser band, same cup volume).

Sister sizes are handy when your calculated band feels too tight or too loose, or when a particular size is out of stock. They are approximate — the fit still depends on the brand and style. To find yours instantly, use our sister size calculator, or read the full explainer in our sister sizes guide.

Common Measuring Mistakes

  • A tape that isn't level. The tape should sit horizontally all the way around your body, front and back. A tape that dips at the back gives a falsely large reading — use a mirror to check.
  • Measuring over a padded or push-up bra. Padding adds inches to the bust measurement that aren't your body, which inflates the cup result. Measure in a thin unpadded bra or without one.
  • Pulling the underbust tape too tight — or leaving it slack. It should be snug enough not to slip, but you should still be able to breathe comfortably. The band does most of the supporting work, so this number matters most.
  • Anchoring to your old size. Bodies change and bras stretch. If you start from the size you "have always worn" instead of fresh measurements, you can carry an old error forward for years.
  • Ignoring brand differences. A calculator gives you a starting size, not a universal truth. Two brands can label the same body differently, so treat the result as the first size to try, not the last word.

Frequently Asked Questions

What is a DDD cup in US sizing?

DDD is the US cup letter that comes right after DD — it represents roughly a six-inch difference between your bust and band measurements. Some US brands label this same cup as F instead of DDD, so 34DDD and 34F from the same brand are usually the same size. Our calculator reports this cup as DDD.

Is a US DD the same as a UK DD?

Yes — US and UK cup letters match from AA through DD, and band numbers are the same in both systems. The two systems only diverge above DD: a US DDD is roughly a UK E, a US G is roughly a UK F, and so on. See the conversion table on this page for the full mapping.

Why is my calculator result different from the size I usually wear?

There are a few common reasons. Brands do not all grade their patterns the same way, so a 34C from one label can fit like a 34B or 34D from another. Older bras also stretch over time, which can make a worn-out band feel like your size when it no longer is. And if your measurements were taken over a padded bra or with the tape at an angle, the inputs may be off. Treat the result as a starting point and try the size — plus its sister sizes — before deciding.

Should I round my band size up or down?

This calculator rounds your underbust to the nearest even inch, which suits most people. If your underbust falls halfway between two even numbers, try both band sizes: the smaller band with a cup letter up (for example, 32D instead of 34C) often gives better support, since bands stretch with wear.

Do US bra sizes use inches or centimeters?

US band sizes are based on inches, and the cup calculation works from the inch difference between bust and band. If you measured in centimeters, just select Centimeters in the calculator — it converts your measurements to inches before calculating.

What should I do if my calculated size is hard to find in stores?

Sizes at the ends of the range — very small bands, very large bands, or cups above G — can be scarce on high-street racks. Specialty lingerie shops and online retailers usually carry a wider range, and sister sizes can open up more options: if 30G is hard to find, 32F (US) holds a similar cup volume on a slightly looser band.

Are sister sizes really the same cup volume?

Approximately, yes. When you go down one band size and up one cup letter — for example, from 36C to 34D — the cup volume stays roughly the same while the band gets firmer. It is an approximation, not an exact science, and the fit can still differ between brands and styles.

How often should I measure myself?

Whenever your bras start fitting differently. Weight changes, hormonal shifts, pregnancy, and aging can all change your size, and elastic wears out over time. A quick re-measure once or twice a year — or any time the fit feels off — is a sensible habit.

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