Bra Size Calculator: Find Your Band and Cup Size
Use our free Bra Size Calculator to estimate your bra size using bust and underbust measurements. Find your band size, cup size, international conversions, and sister sizes in seconds.
What Is a Bra Size Calculator?
A bra size calculator helps you estimate a starting bra size based on your body measurements.
It uses your underbust measurement to estimate the band and your bust measurement to estimate the cup. Our calculator also provides approximate US, UK, EU, and AU/NZ sizes.
Because bra sizing differs between brands and styles, the calculated size is a starting point rather than a guaranteed fit.
How to Use the Bra Size Calculator
Follow these simple steps:
- Select inches or centimeters.
- Choose Quick Size or Detailed Size.
- Enter your required bust and underbust measurements.
- Select your preferred sizing system: US, UK, EU, or AU/NZ.
- View your estimated bra size, band, and cup.
- Compare international sizes and nearby sister sizes.
- Use Copy Result to save your measurements and estimated size.
The calculator updates automatically as you enter measurements.
How to Measure Bra Size at Home
You only need a flexible measuring tape and a mirror to check that the tape stays level.
Step 1: Measure Your Underbust
Wrap the tape around your ribcage directly below your bust.
Keep the measuring tape straight and comfortably snug without causing discomfort.
Record the measurement in inches or centimeters.
Step 2: Measure Your Full Bust
Wrap the tape around the fullest part of your bust.
Keep it level across your back without compressing the tissue.
This is your full bust measurement.
Step 3: Calculate Your Bra Size
Enter both measurements into the calculator.
The tool estimates a band size and cup size using a simplified method that does not automatically add four inches to your underbust measurement.
For additional measurement detail, switch to the six-measurement mode.
Quick vs Detailed Bra Size Calculator
Our tool offers two measurement methods.
| Quick Size | Detailed Size |
|---|---|
| Snug underbust | Loose underbust |
| Full bust | Snug underbust |
| Two measurements | Tight underbust |
| Fast starting estimate | Standing bust |
| Leaning bust | |
| Lying bust |
Quick Size is suitable for visitors who want a fast initial estimate.
Detailed Size uses the average of the standing, leaning, and lying bust measurements to estimate cup size. The loose and tight underbust measurements provide additional context for checking band fit.
Neither method guarantees that a particular bra will fit.
How Is Bra Size Calculated?
Bra sizes usually contain two parts:
- Band size: A number such as 30, 32, 34, or 36 in US/UK sizing.
- Cup size: A letter such as A, B, C, D, or DD.
Our calculator estimates the band by rounding the snug underbust measurement to the nearest even-numbered US/UK band.
It then calculates the difference between the bust measurement and the selected band.
Cup Difference = Bust Measurement − Band Size
Bra Size Calculation Example
Suppose your measurements are:
- Snug underbust: 32 inches
- Full bust: 36 inches
36 − 32 = 4 inches
Using the calculator's cup progression, a four-inch difference corresponds to a D cup.
Your estimated starting bra size is 32D.
This simplified result should always be checked against the fit of an actual bra.
Bra Cup Size Chart
The following chart shows the cup progression used by the calculator.
| Approximate Difference | UK Cup | US Cup |
|---|---|---|
| 1 inch | A | A |
| 2 inches | B | B |
| 3 inches | C | C |
| 4 inches | D | D |
| 5 inches | DD | DD |
| 6 inches | E | DDD |
| 7 inches | F | G |
| 8 inches | FF | H |
| 9 inches | G | I |
The tool also supports additional cup sizes. US cup lettering is not completely standardized across brands, particularly beyond D, so always check the retailer's chart.
US, UK, EU and AU Bra Size Conversion
Bra sizes can use different labels depending on the country.
For example, a starting size of 32D may appear as:
| Sizing System | Example Size |
|---|---|
| US | 32D |
| UK | 32D |
| EU | 70D |
| AU/NZ | 10D |
These are approximate equivalents.
The calculator converts the band and cup labels using its built-in sizing tables. However, different manufacturers may use different cup progressions and garment measurements.
What Are Bra Sister Sizes?
Sister sizes are neighboring bra sizes with approximately similar cup volume but different band sizes.
When the band size decreases, the cup letter generally increases by one step. When the band increases, the cup letter decreases by one step.
For example, the UK sister sizes around 32D are:
| Size | Description |
|---|---|
| 30DD | Smaller band, larger cup letter |
| 32D | Starting size |
| 34C | Larger band, smaller cup letter |
Sister sizes can be useful when the cup volume seems appropriate but the band needs adjustment.
They are not guaranteed to fit identically because band tension and cup shape can differ.
How Should a Bra Fit?
A comfortable bra should provide support without excessive pressure or discomfort.
Check these common fitting points:
- Band: Should sit securely and approximately level around the body.
- Cups: Should contain the breast tissue without unwanted spillage or substantial gaps.
- Straps: Should stay in place without carrying all the support.
- Underwire: If present, should not dig into breast tissue.
- Movement: The bra should feel comfortable when sitting, standing, and moving.
If your band rides up, cups gape, or straps dig in, use the calculator's fit troubleshooting section to explore possible causes.
Why Do Bra Sizes Differ Between Brands?
Bra sizing is not completely consistent across manufacturers.
Even bras with the same size label may feel different because of:
- Band construction and fabric stretch
- Cup depth and shape
- Underwire design
- Strap placement
- Brand-specific sizing charts
- Different international cup-letter systems
For a better fit, use the calculated size as a starting point and compare it with the specific brand's measurements.
Why Use Our Bra Size Calculator?
Our free online calculator includes:
- Quick two-measurement sizing
- Optional six-measurement mode
- Measurements in inches or centimeters
- US, UK, EU, and AU/NZ size estimates
- Band and cup size breakdown
- Sister size suggestions
- International bra size conversions
- Bra-fitting tips
- Automatic calculations
- Copy Result and Reset
Measurements are processed locally in your browser, without requiring an account.
Frequently Asked Questions
How do I know my bra size?
Measure your snug underbust and full bust, then enter both values into the Bra Size Calculator. It will suggest a starting band and cup size.
Can I calculate bra size in centimeters?
Yes. Select centimeters and enter your measurements. The calculator automatically converts the values for its sizing calculations.
What is the difference between band size and cup size?
Band size refers to the numbered measurement around your ribcage. Cup size represents a letter-based difference between bust and band measurements in the selected sizing method.
What bra size is 32-inch underbust and 36-inch bust?
Using this calculator's simplified method, the estimated starting size is 32D.
Are US and UK bra sizes the same?
Some smaller cup sizes use the same labels, but US and UK cup progressions can differ for larger cups.
What is the sister size of 34C?
Common UK sister sizes include 32D and 36B.
Is the six-measurement method more accurate?
It provides additional measurement information, but accuracy still depends on measurement technique, body shape, and bra construction. It does not guarantee a better fit.
Why is my calculated bra size different from my usual size?
Different measurement methods, brand sizing, and cup shapes can produce different results. Your current bra may also use a different sizing convention.
Can bra size change over time?
Yes. Bust and underbust measurements can change over time due to body changes and other factors. Rechecking your measurements can be helpful when your bras no longer fit comfortably.
Is the Bra Size Calculator free?
Yes. You can estimate your size, compare international labels, and explore sister sizes without registration.
Remember: Bra size results are estimates for clothing fit, not medical assessments. The most useful size is one that provides suitable support and feels comfortable on your body.