Bra Size Calculator — Free Online Tool

What Is Bra Size Calculator?

A free online bra size calculator that computes your band and cup size from underbust and bust measurements in inches or centimeters. Converts to US, UK, EU, FR, and AU sizing systems. Includes a comprehensive size chart for reference. Uses standard bra sizing formulas for accurate results.

Finding the correct bra size is surprisingly difficult — studies show that up to 80% of people wear the wrong size. Bra size depends on two measurements: underbust (the band size) and bust (the cup size). Bra Size Calculator computes your size from these measurements and converts between US, UK, EU, FR, and AU sizing systems.

Measure your underbust (directly under your bust, keeping the tape snug but not tight) and your bust (at the fullest part, with the tape loose enough to be comfortable). Enter these measurements in either inches or centimeters. The calculator determines the band size (rounded to the nearest even number) and cup size (difference between bust and band measurements).

The results show your calculated size in all five systems: US, UK, EU, FR, and AU. These systems use different scales — for example, a US 34C is a UK 34C but an EU 75C. The sister size display shows alternative sizes that hold the same cup volume on different band sizes — for example, 34C sister sizes include 32D (smaller band, same volume) and 36B (larger band, same volume).

The complete size chart shows all band and cup combinations from AA through L cups, making it easy to browse related sizes. The calculator uses standard bra sizing formulas: band size is underbust rounded to nearest even inch (with +4 adjustment for certain measurements), and cup size is the difference between bust and band measurements.

Real-World Use Cases for Bra Size Calculator

Finding Your Size for Online Lingerie Shopping

An online shopper measures underbust 30 inches and bust 36 inches. Enter these in inches. The calculator shows US 30DDD/F, UK 30E, EU 65F, FR 80F, AU 8E. The sister size display shows 32DD and 28G as alternatives. Use the US or UK size depending on the brand's origin.

Converting a Known Size to EU for European Brands

A customer knows they wear US 36C and wants to buy from a French brand. Enter US 36C in the known size field. The converter shows EU 80C and FR 95C. The size chart confirms this size across all systems.

Checking Sister Sizes When the Calculator Size Feels Tight

The calculator says 34D but the band feels tight and cups gap. Try the sister size 36C (larger band, smaller cup, same volume). The sister size chart shows all equivalent volume options. The right fit is often the calculator result or one sister size away.

Why Use Bra Size Calculator?

Inches and centimeters support
US, UK, EU, FR, AU conversions
AA through L cup sizes
Automatic band rounding to nearest even

How to Use Bra Size Calculator — Step by Step

Select inches or centimeters.

Enter your underbust measurement.

Enter your bust measurement.

View your calculated size in US, UK, EU, FR, and AU.

Who Is Bra Size Calculator Best For?

online lingerie shoppers
people needing bra fitting
fashion retail

Pro Tips for Bra Size Calculator

1Bra sizing varies significantly between brands. Use the calculator to find your starting size, then check brand-specific size guides and customer reviews for fit guidance.
2Sister sizes (e.g., 34C ↔ 32D ↔ 36B) hold the same cup volume on different band sizes. If the band is too tight, go up a band and down a cup. If the band is too loose, go down a band and up a cup.
3The band should be snug on the loosest hook when new. As the elastic wears, move to tighter hooks. A properly fitted band provides about 80% of the support; the straps should only provide 20%.
4Measurements should be taken while wearing a non-padded bra for the most accurate results. Take measurements at the end of the day when your body has naturally expanded slightly.

Bra Size Calculator — Frequently Asked Questions

How do I measure my underbust?

Measure directly under your bust, keeping the tape snug but not tight. Ensure the tape is level around your torso.

What if my measurement falls between sizes?

The calculator rounds to the nearest even band size and finds the closest cup size. Try neighboring sizes for the best fit.

How accurate are the calculations?

All calculations use double-precision floating-point arithmetic following IEEE 754 standards. Financial calculations like loans and compound interest are verified against standard spreadsheet formulas.

Can I round results to a specific number of decimal places?

Results are typically displayed with up to 10 significant digits. You can mentally round to your desired precision for most practical use cases.

Is Bra Size Calculator really free to use?

Yes, Bra Size Calculator is completely free with no hidden charges, no usage limits, and no premium tiers. You can use it as often as you need without signing up or providing any personal information.

Ready to Use Bra Size Calculator?

Free online tool — works in your browser, no sign-up required. Start using it right now.

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