1 Underbust (Band)
2 Bust (Cup)
Sister Sizes
If the band feels too tight or loose, try these:
International Conversions
Quick Fit Checklist
- The band should be level at the back and firm.
- The gore (centre wire) should tack flat against your sternum.
- Breasts should be fully enclosed (no "quad-boob" spillage).
Why Use Our UK Bra Size Calculator?
Many mainstream sizing guides still rely on the outdated “+4” method, which often puts you into a band that is too large and a cup that is too small. That can lead to poor support, discomfort, and constant readjusting.
This calculator uses modern, UK-first fitting logic to give you a practical starting size. Use Quick Mode for a fast estimate, or Accurate Mode for a better fit using six measurements.
How to Measure for a Bra
1. The Underbust (Band)
Measure around your ribcage directly under your bust. Keep the tape level and parallel to the floor.
- Snug: Comfortably tight (your primary measure).
- Tight: As tight as possible on a full exhale (helps judge firmness).
- Loose: Tape resting on the skin (neutral breath).
2. The Bust (Cup)
Measure around the fullest part of your breasts. Keep the tape lightly touching — do not compress tissue.
- Standing: Normal posture.
- Leaning: Bend forward ~90° (very helpful for projected shapes).
- Lying: Flat on your back.
Frequently Asked Questions
How accurate is this bra size calculator?
This calculator gives a strong starting size using modern UK fitting logic (not the outdated “+4” method). For the best accuracy, use Accurate Mode and take all measurements carefully. Brand and style differences still matter, so treat the result as your starting point and fine‑tune by fit.
Should I add 4 inches to my band size?
Generally, no. The old “+4” method was created for less stretchy vintage materials. Modern bras are designed to fit close to your underbust. Adding 4 inches often causes the band to ride up and removes most of the support.
What are sister sizes and when should I use them?
Sister sizes have the same cup volume with a different band. If the band feels too tight, go up a band and down a cup (e.g., 34E → 36DD). If the band feels too loose, go down a band and up a cup (34E → 32F).
Why does my band ride up at the back?
A band that rides up is usually too big or too stretchy. The band should sit level around your body and do most of the support work. Try a smaller band and increase the cup letter to keep the same cup volume.
What does it mean if the centre gore doesn't sit flat?
The gore is the centre panel between the cups. If it doesn’t tack (sit flat), the cups may be too small, the wires may be the wrong shape for your breast root, or the style may not have enough depth. Try a larger cup or a more projected style.
What is the difference between UK and US cup sizes?
UK and US sizes match up to D, then they diverge. UK uses double letters like DD, FF, GG, while US typically progresses differently (DD, DDD/F, G, H, etc.). This tool shows a conversion table to help when shopping.
Should I measure with a bra on or off?
Ideally, measure without a bra. If that’s uncomfortable, use a non‑padded bra that doesn’t compress or add volume. Keep the tape level and snug, and avoid pulling it too tight for bust measurements.
What if one breast is larger than the other?
That’s very common. Always fit the cup to your larger side. You can tighten the strap slightly on the smaller side or use a removable pad (a “cookie”) to balance the fit.
Disclaimer: Sizing is a starting point. Comfort varies by brand and body shape.