Calculating Bra Size

Finding the correct bra size is essential for comfort, support, posture, and confidence. Studies suggest that many women wear the wrong bra size because they rely on outdated measurements or incorrect fitting methods.

This complete guide explains everything you need to know about calculating bra size, including:

Free Bra Size Calculator
Step-by-Step Measurement Guide
Cup Size Chart
Band Size Chart
UK, US & EU Size Conversion
Sister Size Calculator
Brand Size Comparison
Common Fitting Mistakes
Printable Measuring Guide
Expert Advice
Frequently Asked Questions

Bra Size Calculator

Use the calculator below to estimate your bra size.

Step 1: Measure Your Band

Wrap a measuring tape snugly around your rib cage, directly under your bust.

Example:

Underbust = 31 inches

Round to the nearest even number.

Band Size = 32

Step 2: Measure Your Bust

Measure around the fullest part of your bust while wearing a non-padded bra.

Example:

Bust = 36 inches

Step 3: Calculate Cup Size

Subtract:

Bust - Band = Cup Difference

Example:

36 - 32 = 4 inches

Cup Size = D

Final Bra Size:

32D

Bra Measurement Guide

What You’ll Need

Soft measuring tape
Non-padded bra
Mirror
Pen and paper

Measure Your Underbust

Keep the tape:

Level
Snug
Parallel to the floor

Do not pull too tightly.

Measure Your Bust

Measure around:

The fullest part of your breasts
Keep tape relaxed
Stand naturally

Avoid:

Holding your breath
Raising your shoulders
Wearing a push-up bra

Cup Size Chart

Difference (inches)	Cup Size
1	A
2	B
3	C
4	D
5	DD / E
6	DDD / F
7	G
8	H
9	I

Cup naming may vary slightly by manufacturer and region.

Band Size Chart

Underbust Measurement	Band Size
26–27″	28
28–29″	30
30–31″	32
32–33″	34
34–35″	36
36–37″	38
38–39″	40
40–41″	42
42–43″	44

UK, US & EU Bra Size Conversion

UK	US	EU	France
30	30	65	80
32	32	70	85
34	34	75	90
36	36	80	95
38	38	85	100
40	40	90	105
42	42	95	110

Cup Conversion Example

UK	US	EU
A	A	A
B	B	B
C	C	C
D	D	D
DD	DD/E	E
E	DDD/F	F
F	G	G
FF	H	H

Always check the brand’s sizing guide, as cup lettering can differ.

Sister Size Calculator

Sister sizes have the same cup volume with different band sizes.

Examples:

Current Size	Smaller Band	Larger Band
34C	32D	36B
36D	34DD	38C
32DD	30E	34D
38B	36C	40A

When to Use Sister Sizes

Band feels too tight
Band feels too loose
Cups fit correctly
Brand sizing differs

Video Tutorial

Watching a fitting demonstration can make measuring easier.

A helpful tutorial should show:

How to measure the underbust.
How to measure the bust.
How to calculate cup size.
How to check bra fit.
How to identify common fitting problems

Brand Size Comparison

Sizing can vary between brands because of differences in cup shape, band stretch, and manufacturing.

Brand Type	Band Fit	Cup Fit
Fashion brands	Slightly loose	Standard
Lingerie specialists	True to size	More consistent
Sports bra brands	Firm support	Compression-focused
Luxury brands	Precise sizing	Premium shaping

Tip: If you’re between sizes, compare the brand’s fit guide and read customer reviews before buying.

Common Bra Fitting Mistakes

Measuring Over Clothing

Always measure while wearing a thin, non-padded bra.

Pulling the Tape Too Tight

A tight tape can result in a smaller band size than needed.

Ignoring Sister Sizes

If the cups fit but the band doesn’t, try a sister size before changing cup volume.

Wearing the Wrong Band

A correctly fitted band provides most of the bra’s support.

Keeping Old Measurements

Body shape changes due to:

Weight changes
Pregnancy
Hormonal changes
Exercise
Age

Measure yourself every 6–12 months.

Signs Your Bra Fits Correctly

Band sits level around the body.
Straps stay in place without digging.
Cups fully contain the breast tissue.
Centre gore lies flat against the chest.
No bulging or gaping.
You can comfortably fit two fingers under the band.

Printable Bra Measuring Guide

Expert Advice

Professional bra fitters recommend:

Re-measure every 6–12 months.
Fasten a new bra on the loosest hook to allow for natural band stretch over time.
Replace bras every 6–12 months with regular wear, or sooner if the band loses elasticity.
Different bra styles (balcony, plunge, full coverage, sports) may fit differently even in the same size.
Prioritize comfort and support over the label size if you are between sizes.

Frequently Asked Questions (FAQ)

How do I calculate my bra size?

Measure your underbust to determine your band size, then measure the fullest part of your bust. Subtract the band size from the bust measurement to determine your cup size using a standard cup chart.

What if I’m between two sizes?

Try both your calculated size and a sister size. Different brands and styles may fit differently.

How often should I measure my bra size?

It’s a good idea to remeasure every 6–12 months or after significant weight changes, pregnancy, or hormonal changes.

Why do bras fit differently across brands?

Manufacturing standards, cup shape, band elasticity, and design vary, so the same labelled size can feel different between brands.

What is a sister size?

A sister size has the same cup volume but a different band size. For example, 34C, 32D, and 36B are sister sizes.

Can I calculate my bra size at home?

Yes. With a soft measuring tape and this guide, you can estimate your size at home. Trying on bras is still important to confirm the best fit.

Final Thoughts

Calculating your bra size is the first step toward finding bras that provide the right balance of comfort, support, and confidence. By measuring accurately, understanding band and cup sizing, using sister sizes when appropriate, and checking each brand’s fit recommendations, you can improve your chances of finding a bra that fits well.

For the best results, combine your measurements with a fit check rather than relying on the size label alone. This approach helps ensure that your bra feels comfortable throughout the day and provides the support you need.