sizing
How to Measure Your Bra Size at Home (With a Cup Size Chart)
Most people are wearing the wrong bra size, and often not by a small margin. The reason usually isn't carelessness: measuring takes about two minutes, and almost nobody is shown how to do it properly. This guide walks through it step by step, in centimetres and inches, with a cup size chart, the fit checks that matter more than any number, and how sizing works for wireless bras.
What you need
A soft measuring tape and a mirror. No tape? A piece of string and a ruler work too. Measure without a bra, or in a thin unpadded one, because padding adds centimetres to your bust measurement. Avoid the few days just before your period, when breast tissue can be temporarily swollen (here's why).
Step 1: Measure your underbust (band size)
Wrap the tape directly under your bust, where a bra band sits. Keep it snug but not tight, and level all the way around; use the mirror to check it isn't rising at the back. Breathe out normally and read the number. This is your underbust, and it sets your band size.
- Centimetres (Asian and European sizing): round to the nearest 5. An underbust of 68–72 cm is a 70 band; 73–77 cm is a 75 band.
- Inches (UK and US sizing): many brands round your underbust to the nearest even number, so 31.5 inches becomes a 32 band. Some older US charts add 4 or 5 inches instead, which is one reason the same person can be a different size in different brands.
Step 2: Measure your bust
Wrap the tape around the fullest part of your bust, usually across the nipples. Keep it level and resting on the skin without compressing anything. This is your bust measurement.
Step 3: Work out your cup size
Subtract your underbust from your bust. The difference gives your cup letter:
| Cup | Difference (Asian sizing, cm) | Difference (UK/US, inches) |
|---|---|---|
| A | about 10 cm | 1 in |
| B | about 12.5 cm | 2 in |
| C | about 15 cm | 3 in |
| D | about 17.5 cm | 4 in |
| E / DD | about 20 cm | 5 in |
Put the two together: an underbust of 71 cm (a 70 band) and a bust of 83.5 cm (a 12.5 cm difference) is a 70B. Treat the result as a starting point rather than a verdict. Breast shape, cup depth and each brand's pattern all shift the real fit a little.
Sister sizes: why one number isn't the whole story
Cup letters aren't fixed volumes; they're relative to the band. Going up one band size and down one cup letter keeps roughly the same cup volume, so 70C, 75B and 80A are "sister sizes". That's why one bra size can cover several band-and-cup combinations, and why, if the band feels tight but the cups fit, the usual fix is the sister size (up a band, down a cup) rather than a completely different bra.
Fit checks that matter more than the tape
- The band sits level and doesn't ride up at the back. Most of a bra's support comes from the band, not the straps.
- Two fingers fit under the band, but not much more.
- The cups hold everything without gaping at the top or spilling over the edges.
- The straps stay put without digging in. If they're doing the heavy lifting, the band is too loose.
- It still feels fine at 6pm. A bra that's comfortable in a fitting room but not after a full day isn't the right fit.
Common measuring mistakes
- Measuring over a padded or push-up bra.
- Pulling the tape tight to get a smaller number.
- Letting the tape slope down at the back.
- Relying on a size from years ago. Weight changes, pregnancy and age all change your size.
Sizing a wireless bra
Wire-free styles like Kiri's Every Day Bra hold their shape with four-way stretch fabric rather than a rigid wire, so they're more forgiving between sizes. If you're between two sizes in a wireless style, size up: the stretch takes up any extra room, while a band that's too tight simply digs in. (Period underwear is the opposite: size down.) Our size guide shows which Asian and US/UK sizes fall into each of our sizes (for example, XS covers 70B and 32B), and wireless vs underwire explains how the two support you differently.
When to remeasure
Remeasure after any noticeable weight change, during and after pregnancy or breastfeeding (see what changes after baby), or if it's been more than a year. If your bras have started to dig, gap or ride up, that's usually the sign.
Quick answers
Is band size or cup size more important?
Band size. It provides most of the support, and getting it right usually fixes strap and cup problems too.
Why am I a different size in different brands?
Brands use different sizing systems (centimetres or inches, with or without adding to the underbust) and different patterns. Always check your measurements against a brand's own chart.
Can I measure myself accurately at home?
Yes. Two measurements, a level tape and a mirror are enough to find a reliable starting size, and the fit checks above confirm it.
