UK Bra Size Calculator
Enter your measurements to get a starting UK bra size. This tool works with inches or centimetres and uses common UK sizing logic.
How to use this UK bra fitting calculator
Finding your bra size can feel surprisingly complicated, especially because different brands, styles, and fabrics fit differently. The good news: with two accurate measurements, you can get very close to your ideal UK bra size.
This calculator gives you a starting point, not a final verdict. Think of it as your best first size to try on, followed by a quick fit check and small adjustments if needed.
What you need before measuring
- A soft measuring tape
- A mirror to check tape position
- A non-padded bra (or no bra if preferred)
- 1–2 minutes and relaxed posture
Step-by-step measuring guide
- Underbust: Place tape directly under your bust, keep it level, and pull snug.
- Full bust: Measure around the fullest part of your bust without compressing tissue.
- Use the same unit: Enter both measurements in inches or both in cm.
- Calculate: The tool estimates your UK band and cup size.
How UK bra sizing works
UK bra sizes combine a band size (number) and a cup size (letters): for example, 32F or 36DD.
- Band size reflects your ribcage measurement, rounded to an even number.
- Cup size is based on the difference between full bust and band size.
UK cup progression is unique because it includes double letters after D. A typical sequence looks like: AA, A, B, C, D, DD, E, F, FF, G, GG, H...
| Bust - Band Difference (inches) | Approx UK Cup |
|---|---|
| 0 | AA |
| 1 | A |
| 2 | B |
| 3 | C |
| 4 | D |
| 5 | DD |
| 6 | E |
| 7 | F |
| 8 | FF |
Why your “calculated size” can still vary by brand
Even with perfect measurements, two bras in the same printed size can feel different. This happens because of:
- Different underwire widths
- Stretchy vs firm band materials
- Cup shape (balcony, plunge, full cup, sports)
- Manufacturing tolerance between styles
If one size is close but not perfect, use sister sizing: going up one band means going down one cup, and vice versa. Example: 34E is a sister size to 32F and 36DD.
Quick fit checklist after you calculate
Band fit
- Should feel secure on the loosest hook when new.
- Should sit level across your back (not riding up).
- You should fit roughly two fingers under the band.
Cup fit
- No spillage at top or sides.
- No empty space or wrinkling in the cup.
- Underwire (if present) should sit around breast tissue, not on it.
Straps and center gore
- Straps should support gently, not dig into shoulders.
- The center gore should lie flat against your sternum in wired bras.
Common bra fitting mistakes in the UK
- Measuring over thick clothing
- Using a twisted or angled measuring tape
- Assuming cup letters are absolute (they change with band size)
- Wearing a worn-out bra and blaming the size
- Ignoring shape compatibility (not just size)
FAQ: bra fitting calculator uk
Is this calculator accurate?
It is accurate as a practical estimate when your measurements are accurate. Final fit should always be confirmed by trying bras on.
Can I use centimetres?
Yes. The calculator converts cm to inches internally and then applies UK sizing logic.
What if I’m between sizes?
Start with the suggested size, then test one sister size in each direction. This usually solves “almost right” fits quickly.
How often should I re-measure?
Every 6–12 months, or sooner after weight change, pregnancy/postpartum changes, hormonal shifts, or starting/stopping exercise routines.
Final note
The best bra size is the one that feels supported, comfortable, and stable throughout the day. Use the calculator for direction, then trust a real fit check. A small adjustment can make a big difference in comfort.