size guide

The best way to know your bra size is to spend 5 minutes measuring your boobs.

Use our easy calculator below to input your measurements and get your bra size.

Troubleshooter ... my bra size doesn't show up, what now?

Our calculator measurements cover 28-36 D-J cup sizes. However, our launch size range only has sizes 30-36 D-G.

If you are just outside of our size launch range, you may be within it, if you choose your 'sister size'. There are two simple principles to 'sister sizing':

1. If you go up a back size, go down a cup size. e.g. a 30DD becomes a 32D.

2. If you go down a back size, go up a cup size. e.g. a 36DD becomes a 34E.

If you go up a back size but stay the same cup size, you'll notice extra room in the cup. If you go down a back size but stay the same cup size, the opposite will happen, and you'll notice the cup is tighter.

checking the fit

Once you're in your Impact sports bra, make sure you've adjusted yourself to check its a good fit.

Scoop your boobs into the cups and have the straps done up tight enough! See what 'good' looks like below.


✔️ Boobs comfortably inside the sports bra

✖️ Boobs spilling out the side / showing lots of cleavage (means cup size is too small)

✖️ Gaping fabric (means cup size is too big)


✔️ Fits firmly on the loosest hook

✔️ Level all the way around

✖️ Riding up your back


✔️ As a measure, the hook should be level with or above your armpit.

✔️ Fits firmly

✖️ Digging in (then loosen)️ / too loose (then tighten)


Our fit check service is an easy way to get comfort you're in the right size. Simply drop us an email to with:

1. Details of i) the bra size you bought, ii) your normal bra size, and iii) your underband and cup measurements from the bra calculator.

2. Photos of you in the impact sports bra: front on and side on. Remember to keep your arms relaxed.