Female Fashion TipsStyle Guide
How to Measure Bra Size Correctly (No Fitting Room)
Most women are wearing the wrong bra size — usually a band too big and cups too small. Two minutes at home with a soft tape measure fixes it — no fitting room, no guesswork. Here is how to measure, how to turn two numbers into your size, and the mistakes that change the answer.
The short answer — how to measure bra size
Measure snugly around your ribcage, just under your bust: that is your band size (odd number? round up to the next even one). Measure around the fullest part of your bust, tape level but not tight. The difference is your cup: 1 inch = A, 2 = B, 3 = C — so a 34-inch band with a 37-inch bust is a 34C.
What You Need
Everything you need is probably already in a drawer at home:
- A soft measuring tape — the flexible tailor’s kind, not a metal one.
- A mirror — to check the tape stays level at the back.
- Your best-fitting unpadded bra — or no bra at all.
- Two quiet minutes — standing straight and breathing normally.
Work in inches if you can (centimetres ÷ 2.54) — US and UK sizing is built on them.
Step 1 — Measure Your Band Size
Wrap the tape around your ribcage, just under your bust, where the band sits. Keep it snug — this one should feel firm — and level all the way round; check the mirror for riding up at the back. Breathe out normally and read the number.
Even number? That is your band size. Odd? Round up to the next even number: an underbust of 33 inches means a 34 band, and 31 means a 32.
Forget the old +4 rule
Older advice told you to add 4 or 5 inches to your underbust. That dates from before bands had elastic. Modern brands size from your real underbust number; adding inches gives you a too-loose band — the most common fit problem there is.
Step 2 — Measure Your Bust
Now wrap the tape around the fullest part of your bust, across the nipple line, keeping it level all the way round. The tape should sit flat without digging in — snug is too tight here. Measure it as it is; do not compress it.
Wear a thin, unpadded bra, or measure bare skin. Padding can add an inch or more that belongs to the bra, not to you — and every phantom inch changes your cup.
Step 3 — Work Out Your Cup Size
Your cup size is the difference — bust minus band. Each inch equals one cup size:
| Difference | 0 in | 1 in | 2 in | 3 in | 4 in | 5 in | 6 in |
|---|---|---|---|---|---|---|---|
| Cup size | AA | A | B | C | D | DD | DDD |
Worked example: underbust 33 inches means a 34 band; bust 37. 37 − 34 = 3 inches = a C cup — your size is 34C. US and UK cup letters match up to a D, then part ways; the size chart below covers that.
Sister Sizes: The Same Cup on a Different Band
Sister sizes hold the same cup volume on different bands: a 32C and a 34B hold roughly the same cup — the 34 just spreads it over a longer band. The rule is simple: band up, cup down. Go up one band size, drop one cup letter, and the volume stays the same.
| Smaller band | Same cup volume | Larger band | |
|---|---|---|---|
| 30D | 32C | 34B | 36A |
| 32D | 34C | 36B | 38A |
If a 34B fits in the cup but the band digs in, do not jump to a 36B — that changes the cup too. Try the sister, 36A: same cup, looser band. Most “almost fits” problems end one sister step away.
5 Mistakes That Change Your Size
These five errors turn a correct method into a wrong size:
- Measuring over a padded bra or clothes. Padding and fabric add inches that are not you, inflating your cup size. Measure over a thin unpadded bra, or on bare skin.
- A twisted or sloping tape. If the tape drops or rides up at the back, the reading grows. Check it in the mirror before you read either number.
- Trusting your old bra’s size. Bands stretch with wear, so a two-year-old bra’s printed size describes a bra that no longer exists. The tape is the truth; the label is history.
- Measuring once and never again. Bodies change with weight, hormones, pregnancy and age — the size in your drawer never updates itself. Re-measure once or twice a year.
- Holding your breath or pulling the tape tight. Both shrink the reading. Snug for the band, flat for the bust — and breathe like you are not being measured at all.
Signs Your Current Bra Does Not Fit
Not sure your current size is wrong? Any of these signs means it is time to measure:
- The band rides up your back — too big; your straps are doing its job.
- Your straps dig into your shoulders — the band should carry the weight, not the straps.
- You spill out of the cups — overspill at the top or sides means the cup is too small.
- A brand-new bra only fits on the tightest hook — new bands should start on the loosest hook and move in as they stretch.
When to Re-Measure
Bra size is not a lifetime assignment. Re-measure every 6 to 12 months, and sooner when your body changes: a weight shift of around 5 kg (10 lb), pregnancy and the months after, or hormonal changes such as menopause. Two minutes with the tape keeps every bra you buy honest.
Why Your Bra Size Changes Your Body-Shape Result
Your bust measurement is one of the three numbers that decide your body shape. A padded bra can add an inch to it; a too-small bra can squash an inch away. Either error can nudge you across a boundary — an hourglass reads as a rectangle, a pear as an hourglass — and suddenly the outfit advice you are following suits a different figure.
Measure your bust the same way — thin unpadded bra, tape level, no compression — then put that number into our free Body Shape Calculator to find your shape and best dress styles, and follow the step-by-step rules in our guide to dressing for your body type. Right bra first, right shape second, right dresses third.
Full Bra Size Chart: US, UK and EU
Band sizes convert between US/UK and EU like this:
| Band (US and UK) | 28 | 30 | 32 | 34 | 36 | 38 | 40 | 42 | 44 |
|---|---|---|---|---|---|---|---|---|---|
| Band (EU) | 60 | 65 | 70 | 75 | 80 | 85 | 90 | 95 | 100 |
Cup letters match up to a D, then diverge — a US DDD is a UK E:
| US Cup | AA | A | B | C | D | DD | DDD | G | H | I |
|---|---|---|---|---|---|---|---|---|---|---|
| UK Cup | AA | A | B | C | D | DD | E | F | FF | G |
The bottom line: two measurements and you have a size you can trust — plus sister sizes to fine-tune it. Treat it as a starting point, not a verdict: judge every bra by fit, and re-measure when your body changes. Your shoulders and back will notice the difference before your mirror does.
Related Guides
- Dress for Your Body Type — find your shape with the free body shape calculator.
- How to Dress for Your Body Type — the step-by-step guide that turns your measurements into outfit formulas.
- Female Fashion Tips — every guide on the site, from colour analysis to hairstyles for short hair.
Frequently Asked Questions
How do I measure my bra size at home?
Two numbers and a soft tape measure. Measure snugly under your bust for your band size (round up to the next even number if odd), then measure the fullest part of your bust. Subtract band from bust: each inch of difference is one cup size — 1 inch is an A, 2 a B, 3 a C.
Should I measure with a bra on or off?
Either works, as long as the bra is thin and unpadded — padding adds inches that are not you. Bare skin is most accurate. Avoid push-up bras, and never measure over jumpers or thick tops.
What is the +4 method and should I use it?
The +4 method is an old habit from before elastic bands: add four inches to your underbust to get your band size. With modern stretchy bands it puts almost everyone in a band that is too loose, leaving the straps to do the work. Skip it — brands now size from your real underbust number.
What are sister sizes?
Sister sizes hold the same cup volume on different bands — 30D, 32C, 34B and 36A all hold roughly the same amount. Go up one band size and drop one cup letter to keep the volume. They are your best fix when the cups fit but the band feels wrong.
My two measurements give different sizes in different brands — why?
Bra sizing is not standardised: brands cut bands and cups slightly differently, and fabrics vary in stretch. Your measurements give a starting size, not a guarantee. Try the sister sizes either side and judge by fit — band level and snug, cups smooth, straps comfortable.
How often should I re-measure?
Every 6 to 12 months, and sooner after a weight change of around 5 kg (10 lb), pregnancy, or hormonal changes such as menopause. Bodies shift gradually and bras stretch with wear, so last year’s size quietly stops being true. It takes two minutes.
What if I’m between sizes?
Start with the sister size: band tight but cups right means up a band and down a cup; band loose means the reverse. A new bra should fasten on the loosest hook, saving tighter hooks for when it stretches. Between cup sizes, choose by fit — no spilling, no gaping.
Does bra size affect how my body shape is calculated?
Yes — your bust measurement is one of the three numbers body-shape calculators use, so a bra that squashes or boosts your bust can shift, even flip, your result. Measure in a thin, unpadded bra, or none, for an honest number — then use that same number everywhere, calculators included.