How do I measure for a bra?

Measure your underbust snugly just under your bust for the band, and measure your bust around the fullest part for the cup. Keep the tape level and wear an unpadded bra or none. Both measurements in centimetres are all this calculator needs.

How is the cup size worked out?

The cup comes from the difference between your bust and underbust measurements. Each roughly 2.5 cm, or one inch, of difference is one cup size, so a 5 cm difference is about a B cup and a 15 cm difference is about an E. The calculator does this conversion for you.

Why does my size vary between brands?

Bra sizing is not perfectly standard, so the same labelled size can fit differently across brands and styles. Use this as a starting point, then try the band and cup either side of it. New Zealand uses UK sizing, so your result matches UK labelled bras.

Bra Size Calculator

This calculator turns two simple tape-measure readings into your estimated UK and New Zealand bra size, the band and cup measurement most high-street and online lingerie brands use for sizing. Getting these numbers right matters, because a band that is too loose or a cup that is too small is a common reason bras feel uncomfortable or look wrong under clothing. To use it, measure snugly around your ribcage directly under your bust for the band, and loosely around the fullest part of your bust for the cup, both in centimetres, wearing an unpadded bra or none at all for accuracy. Enter your underbust measurement, covering roughly 58cm to 112cm, and your bust measurement, and the calculator instantly returns your estimated size, for example 34C, along with the band number and cup letter shown separately so you can see how each was worked out. The band comes directly from your underbust reading, while the cup is worked out from the gap between your bust and underbust measurements, with every 2.5cm, about an inch, of difference adding one cup size, from AA through to J. Because bra sizing is not perfectly standardised across manufacturers, treat the result as a starting point rather than a guaranteed fit: try the band and cup sizes either side of your result, and re-measure if your weight changes, since both figures can shift.

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Underbust (band)

Bust (fullest part)

34C

your estimated UK / NZ bra size

Band34

CupC

A guide only. Sizing varies by brand, so try the band and cup either side for the best fit.

How to measure

For the band, wrap the tape snugly around your ribcage directly under your bust, keeping it level. For the cup, measure loosely around the fullest part of your bust. Wear an unpadded bra or none, and measure in centimetres. The band comes from the underbust measurement and the cup from the difference between the two.

How the cup is calculated

The cup size is based on the gap between your bust and underbust. Every 2.5 cm, about one inch, of difference is one cup size. So a 13 cm difference is roughly a DD cup and a 20 cm difference is roughly an FF. Because this is approximate, the size is a starting point rather than a guarantee.

Tips for a good fit

The band should be firm and level, not riding up at the back.
If the band feels loose, try one size smaller and one cup larger.
Re-measure if your weight changes, as both band and cup can shift.

Who this calculator is for

This calculator is for anyone estimating their bra size from band and bust measurements.

What this calculator assumes

The band and bust measurements you enter.
A standard sizing formula based on the difference between the two.
Brands and styles vary, so treat the result as a starting point to try on.

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