Bra Size Calculator
Drag the sliders to your measurements — your size, international conversions, sister sizes and fitting advice update instantly. No sign-up. Completely free.
Units:
⚙ How this calculator works
1
Measure underbust → determine band size
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.
Band Size = round(underbust) → nearest standard band size
e.g. 31″ → 32 · 33″ → 34 · 35″ → 36 · 32″ → 32
e.g. 31″ → 32 · 33″ → 34 · 35″ → 36 · 32″ → 32
2
Measure fullest part of bust
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.
3
Calculate the difference → 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.
Difference = Bust − Band
1″ = A · 2″ = B · 3″ = C · 4″ = D · 5″ = DD/E · 6″ = E/F · 7″ = F/G…
1″ = A · 2″ = B · 3″ = C · 4″ = D · 5″ = DD/E · 6″ = E/F · 7″ = F/G…
4
Combine band + cup → final bra size
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.
Example:
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)
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)
5
International conversions
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.
EU Band ≈ UK Band + 38 cm (approx)
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
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
6
Sister sizes — same cup volume, different band
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.
34B ⇔ 32C ⇔ 36A (all equal cup volume)
36DD ⇔ 34E ⇔ 38D (all equal cup volume)
Rule: go up one band → go down one cup (or vice versa)
36DD ⇔ 34E ⇔ 38D (all equal cup volume)
Rule: go up one band → go down one cup (or vice versa)
📐 Cup size reference chart
Cup size
Difference (inches)
Difference (cm)
AA0 inches or lessLess than 2.5 cm
A1 inch2.5 cm
B2 inches5 cm
C3 inches7.5 cm
D4 inches10 cm
DD / E5 inches12.5 cm
E / F6 inches15 cm
F / G7 inches17.5 cm
FF / G8 inches20 cm
G / H9 inches22.5 cm
GG / H10 inches25 cm
H / I11 inches27.5 cm
📏 How to measure your bra size correctly
1
What you need: A soft fabric measuring tape (not a metal one). Wear a non-padded, well-fitting bra or no bra at all. Stand straight in front of a mirror.
2
Measure your under-bust (band size): Wrap the tape measure snugly around your ribcage, directly under your bust. The tape should be firm but you should still be able to breathe. It must be parallel to the floor all the way around. Breathe out naturally and note the measurement.
3
Measure your bust (cup size): Lean forward slightly at about 45 degrees so your breast tissue falls naturally. Wrap the tape loosely around the fullest part of your bust — usually across the nipple line. Keep the tape parallel to the floor and don’t pull it tight. Stand up straight and note the measurement.
4
Round your measurements: Round each measurement to the nearest whole inch (or cm). If you’re between sizes, round up for a more comfortable fit.
5
Re-measure if unsure: Take each measurement 2–3 times and use the average. Measurements can vary by up to half an inch depending on posture and tape tension.
Under-bust
Bust (fullest point)
⚠️ Common measuring mistakes to avoid
Tape not parallel
If the tape rides up at the back, you’ll get a smaller reading. Always check it’s level all the way around in a mirror.
Pulling too tight
The band tape should feel snug but not constricting. You should be able to slide two fingers underneath it comfortably.
Measuring at the wrong time
Breast tissue can fluctuate throughout your cycle. Measure a few days after your period ends for the most stable result.
Wearing a padded bra
Padded bras add 1–2 cup sizes to your bust measurement. Always measure in a non-padded bra or no bra for accuracy.
Wrong posture
Stand straight with arms relaxed at your sides for the band. Lean forward at 45° when measuring the bust so tissue falls naturally.
Using a metal tape
Metal tapes are rigid and won’t curve around your body accurately. Use a soft fabric or plastic measuring tape only.
❓ Frequently asked questions
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.
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.
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.
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 UK after D.
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.
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.
This calculator provides an estimated size as a starting point. Fit varies between brands and styles. We always recommend a professional in-store fitting for the most accurate result.