First Thing Fit Guide

How to measure your bra:

Not sure of your First Thing size? All you need is some quick measurements to find your perfect size. Make sure you are wearing a non-padded bra to take the measurement. First step is to determine your ‘underbust’ size to get your band size. The second step is to determine your cup size measuring the fullest part of your breasts. Then use the matrix below to find your perfect size. 

Underwire bras size chart showing body sizes 8, 10, 12, 14 and 16, underbust measurements and cup sizes A to E
Wireless Bralette size guide showing underbust sizes 8, 10, 12, 14 and 16 with cup sizes A, B, C, D and DD
Maternity bra size guide
First Thing — Size and fit guide
Sister sizing fit guide

How our Sister Sizing works:

Fit not quite right? Give sister sizing a go! Bra sizes don't work the same way as clothing sizes as the band size varies with the size of the cup like a ratio. So, you can move up & down sizes to find the perfect fit. For example, if you're a 12B but would prefer a firmer fit, then your sister size is a 10C.

Black strapless bra, side view

BRAS

We recommend going down to your sister size in our Strapless Bra for a snug and supportive fit. Take your normal size in the Everyday Bra. If you are between sizes, size down to your sister size. Take your normal size in our Mesh and Lace bras.

Umber G-string underwear, back view

UNDIES

Our undies fit true to size, so we recommend taking your normal size. Depending on how much coverage you like, size up or down accordingly.