UK Bra Size Calculator (Inches)
Use your measurements in inches to get an estimated UK bra size. For best accuracy, measure with a soft tape while braless or in a non-padded bra.
Note: This tool gives a starting point. Bra fit can vary by brand, style, and breast shape.
How UK bra sizing works in inches
UK bra sizes combine a band size (the number) and a cup size (the letter). When you measure in inches, your underbust helps estimate band size, and the difference between bust and band helps estimate cup size.
Example format: 34F, 32DD, or 30G.
Band size (number)
In most modern fittings, the underbust measurement is rounded to the nearest even number (for example, 31.5 becomes 32). Some people still use the traditional “+4” method, where you add 4 inches before rounding. This page lets you try both methods so you can compare.
Cup size (letter)
Cup size is based on the difference between full bust and calculated band size. In UK sizing, cup letters progress with double letters after D:
- 1" difference = A
- 2" = B
- 3" = C
- 4" = D
- 5" = DD
- 6" = E
- 7" = F
- 8" = FF
- 9" = G
- 10" = GG
- 11" = H
- 12" = HH
- 13" = J
- 14" = JJ
- 15" = K
How to measure yourself at home
1) Measure underbust
Place the tape directly under your bust, level around your ribcage. Keep it snug and parallel to the floor. Breathe out normally and record the number in inches.
2) Measure full bust
Measure around the fullest part of the bust. Keep the tape gently resting against the body without compressing tissue. Record this measurement in inches.
3) Enter both values in the calculator
Use decimals if needed (for example, 30.5 or 36.2). Then calculate to get your estimated UK bra size and suggested sister sizes.
Understanding sister sizes
Sister sizes keep a similar cup volume while changing the band. If one band feels too tight or too loose, a sister size can help:
- Go down one band size (e.g., 34 to 32), and go up one cup letter.
- Go up one band size (e.g., 34 to 36), and go down one cup letter.
Example: 34E is close in volume to 32F and 36DD.
Common fit checks after calculating
- Band: Should feel firm on the loosest hook when new.
- Cups: No spilling over or gaping at the top.
- Center gore: Should sit flat against the chest (for most wired bras).
- Straps: Should not carry all the weight or dig in deeply.
UK vs US cup labels
Band numbers are usually similar, but cup lettering can differ between UK and US systems after D. UK brands commonly use DD, FF, GG, and so on. Always check the brand’s own size chart if you are ordering online.
FAQ
Is this calculator exact?
No calculator is perfect. This gives you a strong starting size, then you fine-tune based on fit and bra style.
Why do different brands fit differently in the same size?
Pattern shape, wire width, cup depth, and fabric stretch vary widely across brands and models.
Can my size change over time?
Yes. Weight changes, hormonal shifts, pregnancy, menopause, and activity level can all affect fit. Re-measure every few months if your bras feel different.