Measure Your Bra Size
Drag the sliders to your measurements — your size, international conversions, sister sizes and fitting advice update instantly. No sign-up. Completely free.
Measure snugly around your ribcage directly under your bust. This underbust measurement is then rounded to the nearest standard band size — typically the nearest even number — to produce your band size.
e.g. 31″ → 32 · 33″ → 34 · 35″ → 36 · 32″ → 32
Measure around the fullest part of your chest, keeping the tape parallel to the floor. This is your bust measurement. Cup labels vary by region (US, UK, EU, AU), but the difference between bust and band always determines the cup size.
Subtract your band size from your bust measurement. Each inch of difference maps to a cup size. The progression below applies to UK sizing — US, EU and AU use slightly different labels for the same difference.
1″ = A · 2″ = B · 3″ = C · 4″ = D · 5″ = DD/E · 6″ = E/F · 7″ = F/G…
Your bra size is the band number followed by the cup letter. The same size is expressed differently depending on which country’s sizing system a brand uses.
Underbust = 32″ → Band = 32
Bust = 37″ → Difference = 37 − 32 = 5″
5″ difference → DD/E cup
Final size: 32DD (UK) · 32DD (US) · 70E (EU) · 32DD (AU)
Band and cup labels are written differently across regions. The EU system uses centimetre-based band numbers, while US and AU use the same band numbers as UK but different cup labels at larger sizes.
UK 28 → EU 60 · UK 30 → EU 65 · UK 32 → EU 70
UK 34 → EU 75 · UK 36 → EU 80 · UK 38 → EU 85
Cup labels differ after D:
UK DD = US DD = EU E = AU DD
UK E = US DDD = EU F = AU E
Sister sizes share exactly the same cup volume but use different band and cup combinations. Use them when your exact size is out of stock, or when the band feels right but the cup doesn’t.
36DD ⇔ 34E ⇔ 38D (all equal cup volume)
Rule: go up one band → go down one cup (or vice versa)
FAQs
Why does my bra size vary between brands?
Bra sizing is not globally standardised. Each brand uses slightly different block patterns, grading increments, and labelling conventions. A 34B in one brand may fit like a 34C in another. Always check the brand’s own size guide and try before you buy — or order multiple sizes when shopping online.
What are sister sizes, and when should I use them?
Sister sizes share the same cup volume but use different band and cup combinations. For example, 32C, 34B, and 36A all hold the same volume of breast tissue. Use a sister size when your calculated size isn’t available, or when the band feels right, but the cup doesn’t — try going up a cup and down a band, or vice versa.
How often should I get remeasured?
Your bra size can change with weight fluctuation, pregnancy, breastfeeding, hormonal changes, and even significant muscle gain or loss. As a general rule, remeasure every 6–12 months, or any time your current bras feel noticeably looser or tighter than when they were new.
What’s the difference between UK, US, EU, and AU sizing?
UK and AU band sizes use the same numbers and are nearly identical in cup labelling (both use DD, E, F, FF, G, etc.). US sizing uses the same band numbers but different cup labels — DD is used, but then jumps to DDD instead of E. EU sizing uses centimetre-based band numbers (e.g. 70, 75, 80) and lettered cups that diverge from the UK after D.
My calculated size doesn’t feel right — what should I do?
Calculators give a starting point, not a definitive answer. If the band feels too tight, try the next band size up (and a cup down to maintain volume). If cups gape at the top, try a smaller cup. If underwire digs into breast tissue, try a larger cup. Many department stores and specialist lingerie boutiques offer free professional fittings — these are always worth using.
How do I convert my size to another country’s system?
Your results above show your size in UK, US, EU and AU automatically. If you need a further conversion (e.g. Italian, French, or Japanese sizing), use those figures as your starting point and check a brand-specific conversion chart, as these systems have more variation and are not covered by a single universal standard.