How to Measure Your Bra Size at Home (Australian Bra Size Chart)

If your band has migrated halfway up your back by lunch and your straps are trying to saw through your shoulders, your bra size might need a rethink. Fair enough. Boobs change, bodies change, and most of us have been buying the same size since someone first handed us one in a fluorescent fitting room. Grab a soft tape measure. You’ll need two measurements, a tiny bit of maths and absolutely no advanced boob algebra.

Start with measuring around your ribcage, right under your boobs. That's your underbust. Then measure loosely around the fullest part of your bust. That's your overbust. Underbust in cm gives you your Australian band size (78 cm is a 14). Overbust minus underbust gives you your cup (a 14 cm difference is a C). You can find chart and worked example below.

What your bra size actually means

A bra size is two things stuck together. A band number and a cup letter.

The band number is your ribcage measurement, rounded to Australian sizing. It's the bit that does most of the support work, which is why the band matters more than people think.

The cup letter isn't a fixed boob size. It's the difference between your overbust and your underbust. That's why a 10C and a 14C hold very different amounts of boob, even though they share a letter. Keep that in mind. It comes up again with sister sizing.

How to measure your bra size at home

You need a soft tape measure, a mirror, and about two minutes.

1. Wear an unpadded bra for best results. A padded bra will throw your overbust off.

2. Stand normally. No hunching, no puffing your chest out. Arms relaxed.

3. Measure your underbust. Wrap the tape around your ribcage, directly under your boobs. Snug and level all the way around. Exhale, then read the number in centimetres (78 cm is roughly 30.7 inches, if you prefer imperial).

4. Measure your overbust. Wrap the tape around the fullest part of your bust. Not squashed, not floating off your skin. Level at the back.

5. Measure twice. Bodies move. If you get two different numbers, take the average.

Some brands recommend trying on a few sizes instead of measuring first. That can work, but a tape gives you a much more useful starting point than carrying ten bras into a fitting room.

If you want more detail on our approach, the Nala fit guide walks through it with pictures.

Australian bra size chart

Australian bras run from band 8 to 26, and cups A to H+. Find your underbust cm in the first table for your band. Then find your bust difference in the second table for your cup.

Underbust to AU band size

 

 

Bust difference to cup size

 

How to work out your cup size

Your cup letter only makes sense alongside your band size. Take both measurements to the Nala chart and use the closest match as your starting point.

Sitting on the edge of two sizes? Fabric and cup shape can change how each bra feels, so check the fit once it’s on. Look for cups that contain your boobs comfortably without gaping, squashing or spillage.

Worked example. Your underbust is 78 cm, so your band is a 14. Your overbust is 92 cm. 92 minus 78 is 14. A 14 cm difference is a C cup. You're a 14C.

Landed between cups? If your difference is 15 cm, you're sitting between a C and a D. Try the smaller cup first if the bra has a bit of stretch, and go up if you're spilling out. Between bands works the same way. Try the snugger band first because the elastic will give.

AU to UK, US and EU bra size conversion

Australian sizing sits closest to UK, but the two aren't identical. US uses a totally different band number. EU uses the actual centimetre number for the band. Here's the quick reference.

 

 

Cup letters are worth double-checking too. AU and UK use DD, E, F. US often runs DD, DDD, G. If you're shopping overseas, look up the brand's own chart against your AU size. Our international sizing conversions guide goes deeper if you need it.

Sister sizing, and why your size is not one number

Your bra size comes with close relatives. Sister sizes hold roughly the same cup volume but use different band lengths, which is handy when the cups feel right and the band doesn’t.

• Moving to a larger band? Choose a smaller cup.

• Moving to a smaller band? Choose a larger cup.

The cup capacity stays similar while the band tension changes..

 

 

If the cups fit but the band feels tight, look at the sister size with a larger band. If the band rides up or feels loose, check the smaller-band option. Our sister-sizing guide has more examples.

How to tell if a bra actually fits

The tape gets you into the right neighbourhood. Your boobs get the final say. Once the bra’s on, give it a quick fit check.

• Band: It should sit level all the way around and feel snug, with room for two fingers underneath. If it’s heading north up your back, it’s too big.

• Cups: Your boobs should sit comfortably inside them, with no gaping, bulging or sneaky side escapees.

• Straps: Secure, but not carving their initials into your shoulders. If they’re doing all the heavy lifting, your band is probably too loose.

• Centre front: On an underwire bra, the fabric between the cups should sit comfortably against your sternum. If it’s floating, the cups may be too small or the style may not suit your shape.

The fit mistake we see all the time

A loose band often gets paired with a cup that’s too small. The band creeps up, the straps dig in and your boobs end up squeezed into whatever room is left.

If the cups feel cramped while the band moves around, the size combination needs another look. Use the sister-size table above to find an option with similar cup room and a firmer band. Once it’s on, lift your arms and check that the band stays level across your back.

Fit problems and what they mean

Band riding up your back

A band that keeps climbing your back is too loose. Check the sister-size table above for the nearest firmer option, then make sure the cups still contain your boobs comfortably.

Cups gaping at the top

Two options. The cup is too big, so go down a cup. Or the shape is wrong for your boobs (fuller on the bottom, wider set, higher). Try a different style before you swap sizes.

Cups spilling over the top or sides

Spilling usually means the cup needs more room. Keep the same band and move up one cup first. If the band also feels tight, recheck both measurements before choosing another size.

Straps digging into your shoulders

Your band isn't doing enough work. Tighten the band by going down a size, and the straps will stop taking all the weight.

Underwire poking or sitting on breast tissue

The wire may be the wrong width or shape for your boobs. Another cup style could solve the poking. If your ribs are simply done negotiating with wires, have a look at our wire-free bras. The fit and shape will vary by style, so check the support details before choosing one.

Bra sizing FAQs

Can I measure without a tape?
You can use a piece of string or a phone charging cable, then hold it against a ruler. Not ideal, but it'll get you a ballpark underbust and overbust to plug into the chart.

Does my bra size change?
Yep. Weight shifts, hormonal changes, pregnancy, feeding, coming off the pill, exercise routine changes. Re-measure any time your bras stop feeling right.

Why does the same size fit differently across brands?
Because bra sizing isn't standardised. A 12C in one brand can be a 10D in another depending on cut, stretch and how the brand grades their patterns. Always check the brand's own chart.

What if I'm between sizes?
Try the snugger band first, since the elastic softens with wear. If you're between cups, go smaller if the bra has stretch, bigger if it doesn't.

Is a wire-free bra sized the same?
Start with the same band and cup size. The fit may feel different because each style uses its own fabric and construction, so run through the checklist once it’s on.

How often should I re-measure?
Every 6 to 12 months, or any time your body changes noticeably.

Do I need a professional fitting?
Not to work out your bra size. A tape and this chart will get you there. A fitting can help if you've tried a few sizes and nothing feels right, or if you want a second opinion.

Why doesn't my calculated size feel right?
Usually because the style isn't right for your shape, not the size. Fuller-on-bottom boobs need different cups to wider-set ones. Have a read of how to buy the best bra for your breast shape.

What's the difference between bust size and cup size?
Bust size (overbust) is the full circumference around the fullest part. Cup size is the difference between overbust and underbust. One is a measurement, the other is a calculation.

Does maternity change my bra size?
Almost always. Ribcage expands, boobs grow, and then everything shifts again with feeding. Re-measure through pregnancy and again a couple of weeks after your milk settles. Our maternity bras are cut with all of that in mind.

Where to next

Now you know your size, land on the right style.

• Shop bras across the full range

• Wire-free bras for support without the poke

• Strapless bras for the tops that need one

• Maternity bras for pregnancy and feeding