Bra Size Calculator: Find Your Perfect Fit in Minutes

A bra size calculator will remove all the guesswork from buying a bra by converting two basic measurements into a perfect cup and band size. Ever wonder “what is my bra size?”. Ever found yourself frustrated by a bra that digs in or gapes? 

This guide will take you through all the details of measuring, calculating and converting your bra size without having to go to a fitting room.

How Bra Sizing Works

There are 2 parts to a bra size, the cup size (letter referring to the difference in volume between the bust and the band) and the band size (the number indicating the circumference of the torso). 

Countries can have different measurements and labels, so the same body could be a 34D in the US, a 75E in most of the EU and a 90D in France all of which are correct!

What Is a Bra Size Calculator?

A bra calculator is an online applet that turns the actual band and bust size into a standard size (such as 34B or 36DD). 

Rather than having to rely on the old sizing label, or even a hasty fitting in-store, you input two numbers and receive a size immediately, with conversion to other international sizes when shopping from UK, US, EU or Canadian brands.

Research on bra fitting has always revealed that most women wear their bras the wrong size, typically too loose and too small. The best bra measurement calculator takes away the guesswork, and uses the same formula that professional fitters do.

How to Measure Bra Size at Home

Proper measuring is the key to accurate size measurement of a bra. Place your hands against the back of your head, stand straight with a tight fitting (padded if needed) bra.

Measure your band’s size.

Take the first step: Band size measurement.

Tape the tape snugly, parallel to the floor around your ribcage, directly underneath your bust. This is the bottom bust measurement. Give your answer to the nearest inch. If the number is even, add 4 inches, if it is odd add 5 inches this is your band size.

Step 2 of the fitting process: Measure Bust Size 

Wrap tape around the widest part of your chest, but not so tightly that it is restricting your breathing. This is the bust size that is measured to determine cup size.

Step 3: Determine the size of each cup

In your bust measurement, subtract your band measurement. Every inch is equal to one cup letter:

So if your band is 34 and the bust-to-band difference is 3 inches, your bra size is 34C.

Bra Size Chart by Band and Cup

Use this bra size chart as a quick reference once you know your band and bust numbers.

Because sizing isn’t perfectly standardized across brands, always treat chart results as a starting point rather than a guarantee.

Cup size by region

Band size by region

Common Bra Fitting Mistakes

• Wearing too big a band: A loose band can’t support the bust properly, forcing the cups to work harder.
• Wearing too small a cup: Spillage at the top or sides usually means you need a larger cup, not a smaller band.
• Not re-measuring after weight change: Bra size shifts with weight fluctuation, pregnancy, and even the time of month.
• Ignoring the “sister size”: If a size feels close but not quite right, going up a band and down a cup (or vice versa) often solves fit issues while keeping similar volume.

Why Bra Size Isn’t Always Consistent Across Brands

There is no standard manufacturing for all brands, cuts and fabrics, thus the same size bra might fit differently for each brand. A “36C” in one might feel like a “36B” or “36D” in another. 

That is why a sizing calculator will be a good starting base to use and then try a size larger or smaller within that brand for a best fit in actual use.

Tips for a More Accurate Result

• Measure in the morning or midday, since bust size can change slightly throughout the day.
• Re-measure every 6–12 months, or after significant weight change or pregnancy.
• Always measure over a non-padded bra, not bare skin, for the most realistic reading.
• If your calculated size feels off, try adjacent sizes using the sister-size method before assuming the calculator is wrong.

Frequently Asked Questions

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

Ans: Use a soft tape to measure the underbust (band) and bust (cup) then determine the cup size by using the difference between the measurements and a standard sizing chart. 

Q2: What is the difference between band size and cup size? 

Ans: Band size is the measurement around your ribcage, and cup size is the measurement of the bust in relation to the band.

Your full bra size is a combination of both of these numbers, for example 34C. 

Q3: Why does my bra size differ between brands? 

Ans: Due to slight variations in the size of the molds, fabrics, and proportions of cuts used by manufacturers, sizes are not completely standardised. 

While a calculator provides a good starting point, there can still be a difference in fit across brands. 

Q4: How often should I check my bra size? 

Ans: Band and cup size may change over time and it is good practice to re-measure every 6-12 months or whenever there is significant weight loss or gain. 

Q5: Is a bra size calculator accurate? 

Ans: Yes, provided the measurement is taken right, a bra fitting calculator provides a pretty accurate measurement of a bra size using the same formula as professional fitters would use with some variation between brands, of course, which may require some refinement.