Bra Size Calculator

For the most accurate results,  measure without a bra or shirt on.

Note: Results are in U.S. cup sizes.



Step 1
Wrap the measuring tape around your ribcage (under your bust where the bra band sits). Pull the tape as tightly as you want your bra to fit.


Step 2
Upright Bust
Stand / Sit up straight. Loosely wrap the tape around the fullest part of your bust.


Step 3
Leaning Bust
Lean forward around 90 degrees. Let your breasts hang fully and loosely wrap the tape around the fullest part of your bust.


Step 4
Breast Fullness
If you are Very Center-Full1 (breasts touching when supported), the calculator will add a cup size.
If you are Very Side-Set2 (can fit your palm vertically between breasts when supported), the calculator will go down a cup size.
Very Center-Full1 Very Center-Full
Very Side-Set2 Very Side-Set
Step 5
Fit Preference
With relaxed fit, expect less lift and a more forgiving band. Best for people who don't want to alter the natural shape of their breasts, and prioritize ribcage comfort.

With firm fit, expect more support and a tighter band. Best for people looking for major lift and don't mind a tighter band around the ribcage.

Not sure? We will make a recommendation based on customers in your size range.
Frequently Asked Questions

First, make sure you measured correctly. Measure topless (a bra or even a shirt can mess with the measurements). Pull the tape snug for underbust. Lean forward and let your breasts hang fully when measuring leaning bust. If you are not sure about RELAXED FIT or FIRM FIT, start with FIRM FIT if you want any level of lift.

If the calculator is still giving you a size that puts you in disbelief, we encourage you to give it a try. You could order your current size along with the new size – returns are free. If your shoulder straps fall off, you get spillage, the bra band isn't staying down… we have an inkling that the new size will make a difference. Visible spillage (anything more than a smidge) means at least 2 cup sizes too small. If the bra band is riding up, it's at least 1 band size too big.

The most popular sizes at Understance are 36DDD and 34G. Many of our customers switched from 38C to 36DDD, 46DD to 42K, 34D to 30G… When a bra fits well, your breasts are not smooshed by the cups. They are contained, separated, and lifted.

All size calculators are approximations, but our calculator is off by one size or less 80%+ of the time. If you've visited a store that carries a full size range, tried on several neighboring sizes, and found your best size, stick with that size. However, if you bought your current bra at a big box store that only carries A-DD, then definitely give the new size a try – and see if it unlocks a new world of comfort.

Our calculator uses "plus 0" and "plus 2", depending on your preference for a firm or relaxed fit.

If you prefer a firm and supportive fit, prioritizing shoulder relief and separation, you will get your "plus 0" size. It will be a smaller band size, and a larger cup size.

If you prefer a loose and relaxed fit, prioritizing ribcage comfort and keeping the natural breast shape, you will get your "plus 2" size. It will be a larger band size, and a smaller cup size.

Our size calculator measures your underband differently. Loose underband and tight underband can differ by 4’’ or more. Instead of taking an average of the two, we ask that you measure your underband as tightly as you'd like your bra to fit. If you are familiar with size calculators that take loose, snug, and tight measurements, our measurement will be closest to "snug."

Measure tighter if: your bra band tends to ride up in the back and gets pushed down in front (the “seesaw effect”), the straps are too far apart and cut into your armpit, or you prefer a firm fit.

Measure looser if: you have ribcage sensitivities, you have a more muscular body type, you only want nipple coverage with minimal support, or you prefer a relaxed fit.

We recommend checking the following for the right fit:

1. The bra band should stay put without being uncomfortably tight. It should be parallel to the floor, not riding up in the back.

2. Shoulder straps shouldn’t dig in, slip off, or cut into your armpits.

3. Your breasts should be contained in the cups without overflow or gaps.

4. The underwire should contour your breasts without poking anywhere.

5. Generally, the center gore should lie flat against your chest. However, if your breasts are touching when supported (there is no room for the center gore between your breasts), you are wearing a wireless bra with no center gore, or you have an inverted sternum, the center gore doesn’t need to lie flat against your chest.

Remember to do the "scoop and swoop" (reaching into the bra cups and scooping all the breast tissue into them). Do this every time you put a bra on.

Understance uses U.S. sizing. If you are more familiar with U.K. sizing, here’s a side-by-side comparison of cup sizes: