Bra Size Calculator

About the Bra Size Calculator

Finding the right bra size can be surprisingly tricky — studies show that up to 80% of women wear the wrong size. This bra size calculator takes your underbust (band) and overbust (bust) measurements and determines your bra size in US, UK, and EU systems, complete with sister size recommendations for a better fit.

The difference between your bust measurement and your band measurement determines your cup size. Each inch of difference corresponds to one cup size increment. But sizing isn't universal — a US 34D is the same as a UK 34D but an EU 75D, and cup letter progression differs between systems (the UK uses double letters like DD, FF, GG while the US jumps to DDD/F).

Beyond the basic calculation, it shows sister sizes — alternative size combinations with the same cup volume. If a 34C feels too tight in the band, try a 36B as a sister. The interactive size chart, fit tips, and brand-specific guidance help you navigate the confusing world of bra sizing with confidence.

When This Page Helps

Wearing the wrong bra size causes discomfort, poor support, and faster wear on bras. This calculator turns two body measurements into a size recommendation across US, UK, and EU systems, then shows sister sizes when the first choice is close but not ideal.

It is useful because band and cup sizing vary by region and brand, so a measurement-based result is more reliable than a generic size label.

How to Use the Inputs

1. Measure your underbust (band) snugly around your ribcage, just below the bust.
2. Measure your overbust (bust) at the fullest point, keeping the tape level.
3. Enter both measurements in inches or centimeters.
4. Select your preferred measurement unit.
5. View your calculated size in US, UK, and EU formats.
6. Check the sister size chart for alternative fits.
7. Use the fit guide to troubleshoot common issues.

Example Calculation

Tips & Best Practices

• Measure while wearing a thin, non-padded bra or no bra for the most consistent measurements.
• The band should do 90% of the support work, not the straps.
• New bras should fit on the loosest hook — tighten as they stretch over time.
• Cup size is relative to band size: a 32D cup is smaller than a 36D cup.
• If the center gore doesn't lay flat against your sternum, the cup is likely too small.
• Scoop and swoop breast tissue into the cup after putting on the bra for proper fit.

Understanding Bra Sizing Systems

Bra sizing varies significantly around the world. The US system uses even numbers for bands (30, 32, 34…) and letters for cups (A through N+). The UK system is similar but diverges in cup progression above D, using double letters. The EU system uses centimeter-based bands (65, 70, 75…) with its own lettering.

Common Fit Problems

The most common issue is wearing a band too loose and cups too small. Signs of a poor fit include the band riding up in back, straps digging in (doing the band's support job), cups overflowing or gapping, and the center gore floating away from the chest.

The Sister Size Strategy

Sister sizing is one of the most useful fitting tools. Each row of a sister size chart represents the same cup volume: 30DD = 32D = 34C = 36B. If your calculated size isn't available, moving along the sister size row keeps the same volume while adjusting the band.

Frequently Asked Questions

• How do I measure my underbust correctly?

  Wrap a soft measuring tape snugly around your ribcage, directly under your breasts. Keep the tape level and breathe out naturally. The tape should be firm but not tight enough to dig in.

• What's a sister size?

  Sister sizes share the same cup volume but with different band sizes. For example, 34C, 32D, and 36B are all sister sizes with the same cup volume. Going up a band means going down a cup, and vice versa.

• Why do US and UK sizes differ?

  The US and UK use different cup letter progressions above D. The UK uses DD, E, F, FF, G, GG, H while the US uses DD, DDD (or F), G, H, I. The same physical size can have different letters.

• Should I round up or down for band size?

  Round to the nearest even number. If your underbust is exactly odd (e.g., 33"), try both the size below (32) and above (34) to see which feels better.

• How do EU bra sizes work?

  EU sizes use centimeters for the band (e.g., 70, 75, 80) and the same letter cups but following their own progression. A US 32 band = EU 70, US 34 = EU 75, US 36 = EU 80.

• How often should I get re-fitted?

  Every 6–12 months, or after any significant weight change, pregnancy, or hormonal changes. Bra sizes can change over time due to many factors.

• What if I'm between sizes?

  Try both sizes and the sister sizes. Band stretch, cup shape, and brand variance mean the "right" size can differ between bras. A properly fitting band should be snug on the loosest hook.