Bra Size Calculator

Bra Size Calculator: Find Your Size in Under a Minute

This bra size calculator will give you an accurate size based on only two measurements, your band and your bust. Enter in either inches or centimeters, and you will see your size in US, UK, EU and AU systems side by side so you know exactly what to look for no matter where you are buying. The entire process takes less than a minute, and all you need is a soft tape measure and a couple of minutes in front of a mirror.

(Bra Size Calculator Tool: Band Measurement | Bust Measurement | Unit Toggle (Inches/cm) | Region Output: US, UK, EU, AU shown together)

How to Measure Yourself for a Bra Size Calculator

And you can’t get an appropriate size without a bra size calculator. This is how it’s supposed to be done:

• Measure your band up. Be sure the tape is even all the way around your back and wrap it tightly around your rib cage, just below your bust. “Snug” means you can slide one finger underneath, not loose and not squeezing. 

• Take bust measurement. Wrap the tape around the largest section of your bust so that it is level, but not tight or compressed.

• Please wear clothing appropriate for measurement. Do this in a non-padded bra or no bra at all, standing up straight with your arms relaxed at your sides. A padded or push-up bra will throw off your bust measurement. 

This is where almost everybody gets confused. Measuring your band in inches is NOT your real band size. If your underbust measurement is an odd number, add 4. If it comes out odd, add 4. So a 30-inch underbust (even) becomes 35, which then rounds to the nearest band size sold, usually 34 or 36. It looks like a weird regulation, but it exists because band sizing was standardized decades ago around this exact modification, and it’s stuck ever since. 

Your bust measurement, on the other hand, translates straight to your cup size if you compare it against your band size, which gets us to the calculation itself. 

How to Calculate Bra Size (The Formula)

Now you have your two measurements, working out your bra size guide calculator is a simple two-step process.

Step 1: Band Size (in.) If your underbust measurement is an odd number, add 4. If it is odd, add 4. Round up to the nearest even number, as that’s what is actually sold in stores.

Example: 28″ underbust measurement (even) -> 28 + 5 = 33 -> rounds to the nearest sold size, 34 

Step 2: Size of cup Measure your bust and remove the band size number (the real bust to band difference before the last rounding). Each inch of difference is a letter: 

• 1 inch difference = A
• 2 inches = B
• 3 inches = C
• 4 inches = D
• 5 inches = DD/E
• 6 inches = DDD/F

Full worked example Underbust measurement of 28 inches (which equates to a 34 band) and 37 inches bust. The difference is 37-34=3 inches which is a C cup. 34C size.

This method of bra size calculation in inches works whether it is your first time measuring or you are double-checking a bra size you’ve been wearing for years, because bras expand and bodies alter.

Bra Size Calculator: US, UK, AU and EU Compared

One size doesn’t mean the same thing everywhere, and this trips up a lot of people shopping from overseas brands. Here’s how a few common sizes line up across systems:

Two patterns are worth knowing. First, band numbers stay close between US, UK, and AU systems, while EU sizing uses a completely different scale based on centimeters, so a 34 band becomes a 75 in EU. Second, and this is the number one source of confusion, cup letters start to shift by one letter between the US and UK/EU systems once you get above a D cup. A US DD is a UK E. A US DDD (or F) is a UK F. Below a D cup, the letters usually match up fine, which is exactly why the mismatch catches people off guard the first time they buy from a UK or European brand.

Bra Size Calculator USA

In the US system it is usually DD or DDD after a D cup and sometimes G or H for the bigger sizes. All with the same one-inch-per-letter rule from the above formula.

Bra Size Calculator UK

The UK method uses the same band size math, but the cup letters go forward. In the UK size it skips DD and goes from D to E, then F, FF, G etc. If you’re used to US sizing this is usually the biggest change.

What Is a Sister Size? (And Why You May Need One)

A sister size is the same cup volume but a different band measure with the help of a bra cup size calculator. If you are in your size in the cup but it is tight in the band or vice versa, usually a sister size is the fix, not an entirely new size range.

The rule is easy. Either go up a band size and down a cup size, or go down a band size and up a cup size, the cup volume will be about the same either way.

For example, if the 34C fits your ribcage but the cup is good try a 36B. The larger band provides your ribcage more room, while the smaller cup letter preserves the same overall capacity, because a larger band spreads that volume out more.

This is particularly beneficial if a company doesn’t stock your exact size or your band size has changed slightly but your cup volume has not. 

Signs Your Current Bra Size Is Wrong

Here are some obvious signs that you need to recalibrate:

• The band rides up your back. It should be level, parallel to the ground, not creeping up during the day.
• Straps cut into your shoulders. Most of the support should come from the band, not the straps. 
• The cups gape or spill over. Gaping usually suggests the cup is too big; pouring over the top or sides usually means it’s too small. 
• The middle gore is not flat. The center piece between the cups should rest flat against your chest, not float above it. 

None of these symptoms suggest you are doing anything wrong. Bodies alter, bras stretch, and companies cut sizes differently, so recalculating is just basic maintenance. 

When to Re-Measure Your Bra Size

Re-measure every 6-12 months or so. Bra elastic will stretch out with regular wear, even if nothing about your body has changed. Anytime you detect this routine check re-measure:

• Weight change, gain or loss
• Pregnancy or postpartum
• Initiating or discontinuing some drugs affecting body composition
• Postoperative recovery

There’s no such thing as a forever set-in-stone size, and it takes but a minute with a tape measure to check again.

Conclusion

Getting your size right with the help of a bra size calculator makes a bigger difference to comfort than most people expect, and it only takes two measurements and a couple of minutes to get there. If your current bra shows any of the fit issues above, band riding up, straps digging in, cups gaping, it’s worth remeasuring rather than assuming the size on the tag is still accurate for your body today. And if the exact size you calculate isn’t available from a brand you like, try the best bra size calculator first before assuming nothing will fit. Bodies change over time, so treat this as something worth rechecking, not a one-time task.

Frequently Asked Questions

Q1. How do I calculate my bra size at home?

Measure comfortably around your band just below your bust and around the fullest point around your bust. Then depending on whether it is odd or even add 4 or 5 to your band measurement. Then subtract your bust measurement from your band measurement. This is your cup letter.

Q2. Why do UK and US bra sizes have different cup letters?

Below a D cup the two systems usually match. They differ above D.A US DD is a UK E and a US DDD is often a UK F. It is just another name for the same measurement.

Q3. What is a sister size and how do I find mine?

Sister size is the same cup volume in a different band size. If you go up one band size and down one cup size, or down one band size and up one cup size, the volume is about the same.

Q4. Should I measure over or under my bra?

Measure without a bra or with a non-padded bra for most accurate measurement. Most important thing is to be consistent with each measurement so you are tracking real changes not discrepancies in measurement.

Q5. Why do I get a different size at every store?

There is no common production standard from brand to brand, so the cut, the stretch in the fabric and the philosophy on size all differ. It’s usual to get a slightly different size at different retailers, not a sign you measured wrong.

Q6. How often should I recheck my bra size?

A decent thumb rule is 6 to 12 months or sooner if you observe any alteration in your physique. Even if your figure doesn’t change, the band and straps stretch out with regular wear.