How to measure for a bra when Japanese sizing feels off

Japanese bra sizing is based on the JIS standard, which uses the underbust measurement in centimetres for the band and a cup letter system where the difference between underbust and bust determines the cup. If you have only ever bought bras sized in European or US notation, the conversion is not immediately obvious.

The JIS band and cup system ¶

In the JIS system, band sizes run in 5-centimetre increments: 65, 70, 75, 80, 85, and so on. The band size corresponds to the underbust measurement in centimetres, measured on an exhale. If your underbust measures 73 centimetres, you would typically try a 70 band first, then a 75 if the 70 feels restrictive.

Cup sizes in the JIS system use the difference between the bust measurement (at the fullest point) and the underbust measurement. A 10-centimetre difference is an A cup, 12.5 centimetres is a B cup, 15 centimetres is a C cup, and so on in 2.5-centimetre increments. This is similar to the UK system but the increments differ slightly from European sizing.

Where bras behave differently from structured bras ¶

bras do not have rigid cups, underwire channels, or boning, so the fit logic is slightly different. The band is the primary source of support, and it needs to sit firmly without digging in. For styles, we recommend measuring the underbust on an exhale and rounding to the nearest band size rather than sizing down for a tighter fit.

The cup in a bra is knitted with varying stitch density rather than moulded foam, so it has more give than a structured cup. If you are between cup sizes, the construction will usually accommodate the smaller of the two sizes without gaping.

What to do if you are between sizes ¶

If your measurements fall within 2 centimetres of the upper threshold for a given size, go up. The fabric has enough stretch to accommodate, and a slightly larger band will not sag or lose its position during the day. Going down when you are between sizes is the most common cause of a band that feels tight by mid-afternoon.

If you have your measurements and are still unsure, send them through the contact form. We will give you a specific recommendation based on the style you are considering.