Bra Size Calculator

Use our free bra size calculator to find your perfect fit. Enter your measurements and get instant results in US, UK, EU, and 7+ international sizing systems.

Underbust / Band Measurement (measure snugly around ribcage, just below breasts)

inches

Bust Measurement (Standing) (measure at the fullest point of your bust)

inches

Your data is never stored or shared. All calculations happen in your browser.

Enter your measurements to see your bra size results here

Results include US, UK, EU, FR, IT, AU, and JP sizes

How Our Bra Size Calculator Works

Finding a comfortable bra size starts with two simple measurements: your underbust (band) and your fullest bust point. Our calculator applies standard sizing formulas used by many lingerie brands and converts the result into US, UK, EU, and other common labeling systems. Treat the output as a strong starting point—not a final verdict—because fit varies by brand, style, fabric, and body shape.

Many women report wearing a size that feels slightly off, and industry estimates often suggest that a noticeable share of shoppers could improve comfort by remeasuring and trying nearby sizes. This tool helps you begin that process at home with clear numbers you can compare against size charts and sister sizes.

What You Need Before You Measure

Gather a soft measuring tape, a mirror, and a well-fitting unpadded bra or no bra at all. Stand naturally with arms relaxed at your sides. Measure on bare skin or over a thin, non-compressing layer. Write down each number to the nearest half inch or centimeter.

Underbust (band): Measure directly under the bust where the band sits, keeping the tape level all the way around.
Bust: Measure around the fullest part of the chest, usually across the nipple line, without pulling the tape tight.
Posture: Breathe normally. Do not suck in or push the chest forward.

If possible, ask someone to help you keep the tape parallel to the floor. A skewed tape is one of the most common reasons home measurements disagree with store fittings.

Step-by-Step: Band and Cup From Measurements

Step 1 — Measure the band

Wrap the tape snugly under your bust. It should feel firm but not painful. Round to the nearest half inch. For US sizing, many charts add inches to the raw underbust measurement to determine band size, while UK and EU systems may use centimeters mapped to labeled bands. Our calculator handles those conversions so you do not have to memorize regional rules.

Step 2 — Measure the bust

Measure at the fullest point. The tape should rest lightly on the skin without compressing breast tissue. Note the reading and subtract your band-related measurement according to the system you are using. The difference between bust and band corresponds to cup volume in alphabetical steps (A, B, C, D, and so on).

Step 3 — Enter values and review results

Input your numbers into the calculator above. You will see a primary size plus equivalents in other countries. Compare with your current bra: if the band rides up, you may need a smaller band and larger cup (sister size). If cups gape, try a smaller cup or a different cup shape.

Reading Your Results: Band vs Cup

The band provides most of the support—roughly 80% of lift in a well-designed bra comes from the band, not the straps. A band that is too loose will climb up the back; too tight may cause digging and shallow cups. Cups should encapsulate tissue without spillage at the top or sides. Center gore should lie flat against the sternum in many full-coverage styles, though plunge and bralette cuts differ.

Cup letters are not absolute volumes. A 34C and a 36B can hold similar breast volume (sister sizes) but distribute it differently around the body. That is why trying both your calculated size and one sister size up or down often improves fit faster than chasing a single letter.

When to Remeasure

After weight change of more than 10–15 pounds
During or after pregnancy and nursing
Following major hormonal shifts or surgery
When your current bras consistently fail the fit checks below
Every 12–18 months as bodies change gradually with age and activity

Practical Fit Checks After You Calculate

Use these quick tests when trying on bras in your calculated size:

Band level: The back band should sit horizontal, not rising toward the shoulders.
Two-finger rule: You should fit two fingers under the band at the back hook; tighter on the loosest hook when new.
Cup containment: No quad-boob at the top; no empty space at the apex.
Straps: They should not carry most of the weight; adjust so they stay up without digging.
Movement: Raise arms; the band should not shift dramatically.

Brand and Style Variance Disclaimer

Sizing is not standardized across manufacturers. A 34D in one brand may feel like a 32DD in another. Demi cups, balconettes, sports bras, and bralettes fit differently even at the same labeled size. Fabric stretch, hook placement, and wire width all change how a size feels. Use our calculator output as a map, then confirm with try-on or retailer size guides.

Common Mistakes That Skew Calculator Results

Measuring over a padded bra that adds volume to the bust reading
Pulling the tape too tight on the underbust
Standing at an angle so the tape is not level
Rounding inconsistently (mixing half inches with whole inches)
Measuring immediately after exercise when the chest is swollen

Repeat measurements twice and average if they differ by more than half an inch. Consistency matters more than perfection.

Next Steps on BraSizeHelper

Explore our how to measure guide, compare numbers on the measurement chart, or use the sister size calculator if you are between band sizes. For international shopping, see bra size conversion.

Bra Size Estimator, Calculator & “Figure Out My Size” Searches

People search for a bra size calculator, bra calculator, bra size estimator, or phrases like “figure out bra size” and “determine bra size.” They usually want the same outcome: a starting band and cup from underbust and bust measurements.

This tool is built for that workflow. Enter inches or centimeters, choose standard or advanced mode, and review sister sizes when a brand runs tight or loose. Then confirm fit on the body—calculators estimate; try-ons decide.