Bra Size Calculator
Enter your underbust (band) and bust measurements to estimate your US bra size.
Example
With a band (underbust) of 32" and a bust of 36", the band size is 32 and the difference is 4 inches, giving a D cup, so the estimated size is 32D.
How it works
Band size = your underbust measurement rounded to the nearest even number. Cup size comes from the difference between bust and band: each full inch of difference is one cup (1"=A, 2"=B, 3"=C, and so on, with 0" or less = AA).
Good to know
The Bra Size Calculator turns two tape-measure readings — your band (underbust) and your bust (fullest point) — into an estimated US bra size like 32D. It's built for anyone shopping online without a fitting room, restocking a favorite style, or simply checking whether their current size still matches their body after weight, hormonal, or postpartum changes. Everything is computed live in your browser, so the two numbers you type never get sent anywhere.
Reach for it before buying online, when a band feels too tight or loose, or whenever a new brand's sizing leaves you guessing. To read the output, look at the three stats it breaks out: the band size is your underbust rounded to the nearest even number, the difference is bust minus band in inches, and the cup is the letter that difference maps to. The big combined figure (band number plus cup letter) is what you'd actually search for on a label.
One practical note on how this particular tool works: it rounds the band to the nearest even number rather than adding the older "+4 inches" allowance that many vintage charts used, so the number you get is closer to modern boutique and "true to body" sizing. If a brand still uses the +4 method, you may find their tag runs a band size larger than this estimate.
A few things to keep in mind: measure the band snugly and level, and the bust loosely over a thin non-padded bra for the most reliable difference. A 0-inch or negative difference reads as AA, and very large differences fall into the calculator's DD, DDD/F and beyond range — but because cup volume and band fit interact (sister sizing), treat the result as a starting point and try the size above and below it.
Frequently asked questions
How do I measure for band and bust?
For the band, wrap a tape snugly around your ribcage just under your bust and keep it level. For the bust, measure loosely across the fullest part of your chest while wearing a non-padded bra. Both should be in inches.
What does the bust-minus-band difference mean for cup size?
Each inch of difference roughly equals one cup size: about 1 inch is an A cup, 2 inches a B, 3 inches a C, 4 inches a D, 5 inches a DD, and so on. A difference of 0 or less is an AA cup.
Is my data uploaded anywhere?
No — this calculator runs entirely in your browser. Your inputs never leave your device, and it works offline once loaded.
Is this calculator free?
Yes, completely free with no sign-up and no limits.
People also ask
What bra size is a 32 band and 36 bust?
A band of 32 inches stays at band size 32, and a 4-inch difference between bust and band gives a D cup, so the estimated size is 32D.
Should I add 4 inches to my band measurement for bra size?
This calculator does not add 4 inches; it rounds your underbust to the nearest even number, matching most modern sizing. The older +4 method tends to produce a looser, larger band, so use it only if a specific brand's chart calls for it.
How many inches is each cup size?
Roughly one inch of bust-minus-band difference equals one cup: about 1 inch is A, 2 is B, 3 is C, 4 is D, and 5 is DD, with 0 inches or less counting as AA.
Why does my bra size feel wrong even though I measured carefully?
Fit varies a lot by brand, style, and fabric stretch, and band and cup interact through sister sizing. Use the calculated size as a baseline and try the size above and below it.
Can I measure my bra size at home without a fitting?
Yes. With a soft tape measure you only need two numbers — a snug, level band reading just under the bust and a loose reading across the fullest part — and the calculator does the rest.
Does this bra size calculator work in UK or EU sizes?
No, it estimates US sizing only. US, UK, and EU systems use different band numbering and cup letters, so you'd need a separate conversion chart to translate the result.
What does a negative or zero difference between bust and band mean?
It means there is little to no cup volume above the band, which the calculator reports as an AA cup, the smallest size it offers.
Should I measure my bra size with a bra on or off?
Measure the band directly against your ribcage, and measure the bust over a thin, non-padded bra so the fullest point is captured without extra padding skewing the difference.
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