Teen Bra Size Calculator
Finding a first size, or a new size after things changed again, takes two measurements and two minutes. Enter them below and you will get a starting size plus its sister sizes. Everything runs on your device; nothing is saved, sent or seen by anyone but you.
Whatever the result says is simply geometry, a band number and a volume letter. It is not a grade, not a comparison to anyone, and it will probably change again, because sizes usually keep shifting into the early twenties. That is the body doing exactly what it is supposed to do.
This calculation runs entirely in your browser. Your measurements are never stored or sent anywhere.
Measuring alone or with help, both are fine
You can do this solo in front of a mirror: wrap the tape snug and level around your ribcage right under your bust, breathe out normally, note the number. Then measure loosely around the fullest part. If a parent or someone you trust is helping, they hold the tape ends level at the back; either way takes a minute. Measure without a padded bra on, or braless if you are comfortable.
First bras do not need underwires or padding unless you want them. Soft crop styles, bralettes and light t-shirt bras cover most needs while sizes are still moving, and they are easier to fit correctly. What matters is a band that stays put without digging and cups that hold everything without squeezing.
When to measure again
Every three or four months during growth years, or sooner if a bra that fit starts digging, gaping or riding up. Keep the receipt habit: buy one or two at a new size, not five, because the size may move within the year. And if one side is a little bigger than the other, that is true for most people at every age; fit the larger side and the smaller one will be fine.
Frequently asked questions
Last updated August 2026.