First Thing Fit Guide

How to measure your bra:

Not sure of your First Thing size? 

Our measurement chart is a helpful guide to finding your recommended size. Make sure you wear a non-padded bra and use a soft measuring tape. 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 as a guide only. 

Breast shape, volume, bra style and your preferred band fit can all influence your ideal size. For the best guidance on fit, also check the Size & Fit notes on each product page.

How our Sister Sizing works:

Fit not quite right? Try sister sizing! Go down a band size and up a cup for a firmer fit, or up a band size and down a cup for a looser fit — with the same cup capacity.

  • The Strapless - Black, Bras - First Thing Underwear

    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.

  • The G-String - Umber, Undies - First Thing Underwear

    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.