How to Measure Your Bra Size at Home
(UK Guide)
A proper UK bra measurement only takes two readings and a soft tape measure. Get these right at home and the calculator does everything else — band size, cup letter, sister sizes, EU equivalent. No appointment needed.
Step-by-Step Guide
Works in centimetres and inches. All UK bra sizes supported.
Measure Your Underbust
This is the number that becomes your UK band size — the 32, 34, or 36 on the label.
- → Remove your bra, or wear one with no padding or lining
- → Wrap the tape around your ribcage, directly beneath your bust where the band would sit
- → Pull it firm against your skin — snug enough not to slip, but not crushing
- → Use a mirror to check the tape sits perfectly level all the way around
- → Write down the number in cm or inches
Measure Your Bust
Subtract your underbust from this number (in inches) and the result tells you your cup letter.
- → Lean forward about 45 degrees before placing the tape — this lets your breast tissue fall into its natural position
- → Place the tape around the widest part of your bust
- → Keep the tape touching your skin without compressing or bunching
- → Breathe normally while you read the number
- → Record it in the same unit as your underbust (both cm or both inches)
Enter Your Measurements
Type your two numbers into the calculator and you'll have your UK band, cup, sister sizes, and EU equivalent in seconds. No rounding, no guessing — just your result.
Inches to Cup Size: The Complete UK Conversion Chart
If you want to calculate your cup size manually, subtract your snug underbust measurement from your full bust measurement. Use the resulting difference in inches to find your corresponding UK cup letter below. Notice how UK sizing uses double letters (DD, FF, GG, HH, JJ) after D!
| Bust Minus Underbust (Inches) | UK Cup Letter |
|---|---|
| 0 inches (< 0.5") | AA |
| 1 inch (1.0") | A |
| 2 inches (2.0") | B |
| 3 inches (3.0") | C |
| 4 inches (4.0") | D |
| 5 inches (5.0") | DD |
| 6 inches (6.0") | E |
| 7 inches (7.0") | F |
| 8 inches (8.0") | FF |
| 9 inches (9.0") | G |
| 10 inches (10.0") | GG |
| 11 inches (11.0") | H |
| 12 inches (12.0") | HH |
| 13 inches (13.0") | J |
| 14 inches (14.0") | JJ |
| 15 inches (15.0") | K |
Why UK Cup Math is Different
In US and EU sizing systems, double letters are rare or non-existent (e.g., US DDD is UK E, US G is UK F). When buying British brands like Bravissimo, Freya, Panache, or Marks & Spencer, always rely on this UK cup progression so you don't end up two or three cup sizes too small!
What You Need to Measure Your Bra Size
Good news: the kit list is very short.
A dressmaker's or tailor's tape works best. A rigid ruler won't follow the curves of your body accurately.
Useful for checking the tape is completely level at the back — even a small tilt can change your reading by an inch.
That's genuinely all it takes. Two measurements and the calculator handles everything else.
UK Cup Size Difference Chart
Subtract your underbust from your bust (both in inches) and match the result to a cup letter below.
| Difference (inches) | Difference (cm) | UK Cup Size |
|---|---|---|
| Less than 1" | Less than 2.5 cm | AA |
| 1" | 2.5 cm | A |
| 2" | 5 cm | B |
| 3" | 7.5 cm | C |
| 4" | 10 cm | D |
| 5" | 12.5 cm | DD |
| 6" | 15 cm | E |
| 7" | 17.5 cm | F |
| 8" | 20 cm | FF |
| 9" | 22.5 cm | G |
| 10" | 25 cm | GG |
| 11" | 27.5 cm | H |
Common Bra Measuring Mistakes
These four errors account for most wrong-size results when measuring bra size UK.
❌ Measuring over a padded bra
Measure on bare skin or wearing an unlined, unpadded bra. Padded cups add bulk that artificially inflates your bust reading and pushes your cup letter up.
❌ Pulling the underbust tape too tight
Snug is correct — squeezing is not. Over-tightening your underbust gives a band number that is too small, which then throws the cup calculation off by a size or more.
❌ Letting the tape angle downward at the back
Check in a mirror that the tape is running straight and level all the way around. Even a small downward tilt at the back adds length to your underbust reading.
❌ Applying the old +4 formula
Adding 4 inches was a workaround for rigid, non-stretch fabrics used decades ago. Modern bra bands use elastane and Lycra — they stretch. Use your actual ribcage measurement for an accurate, supportive band.
How to Measure Bra Size UK When Pregnant
The technique is the same whether you're pregnant or not — underbust and bust into the calculator. But your size changes rapidly during pregnancy, especially around the ribcage and across the cups. Most women find they move up one or two band sizes and two to four cup sizes between early pregnancy and established breastfeeding.
Remeasure every four to six weeks during pregnancy and while nursing. Rather than buying a full set of maternity bras at once, buy a couple at around 16 weeks, more at 32 weeks, and then nursing bras around six to eight weeks after the birth once your milk supply has settled.
When to Remeasure Your Bra Size
Most women's bra size changes more often than they realise. Every six months is a good habit, but remeasure sooner if you notice your bras feeling differently than usual.
- ✓ After any weight gain or loss of 5+ lbs
- ✓ During and after pregnancy
- ✓ After surgery or hormonal changes (e.g. new contraception)
- ✓ When your current bras suddenly feel different — tighter, looser, or uncomfortable
- ✓ After the menopause
Shopping a US, EU or Australian Brand?
Once you know your UK size, convert it instantly to US, EU, Australian, and French sizing using our dedicated tool.
International Size ConverterMeasuring FAQ
How do I measure my underbust for a UK bra size?+
Wrap a soft tape measure firmly around your ribcage, directly below your bust where the bra band sits. Pull it snug — firm enough that it won't slide down, but not so tight you can't breathe. Keep it completely level front to back, and note the measurement in cm or inches. Round to the nearest even number to get your UK band size.
Should I measure my bra size in cm or inches?+
Either works fine — our UK bra size calculator accepts both. Most UK bra sizes are labelled with inch-based band numbers (28, 30, 32…), but measuring in cm is equally accurate. Just make sure you enter both measurements in the same unit.
What if my measurements fall between two sizes?+
For the underbust, round up to the next even number if you fall between. For example, 31 inches rounds to 32, and 33 inches rounds to 34. Bands stretch, so starting slightly firmer is better than starting too loose. For the cup, if you fall exactly between two letters, try both — bra styles vary enough that one will almost certainly feel better.
How tight should my underbust measurement be?+
Firm but not tight. The tape should sit flush against your skin without compressing it. A useful check: you should be able to slide one finger under the tape, but not two. This is also roughly how your finished bra band should feel on the loosest hook when new.
Do I measure over or under my clothing?+
Measure on bare skin or over a thin, unpadded bra. Measuring over padded cups or thick clothing will inflate your bust reading and give you an inaccurate cup size. If you're wearing a bra for the measuring process, choose an unlined, non-padded style.
How do I measure bra size UK when pregnant?+
The technique is exactly the same — underbust and bust measurements entered into the calculator. However, your size changes significantly and quickly during pregnancy, so remeasure every 4–6 weeks rather than waiting 6 months. Most women go up 1–2 band sizes and 2–4 cup sizes during pregnancy and early breastfeeding. Buy maternity bras in stages rather than all at once.