Find Your Starting Bra Size
Enter your measurements to estimate a comfortable bra size. This calculator gives a strong starting point for band size and cup size.
Tip: Measure while standing straight, wearing a non-padded bra, and keeping the tape level all around.
How this bra size calculator works
A bra size has two parts: a band size (the number) and a cup size (the letter). The band comes from your ribcage measurement, while the cup comes from the difference between your full bust and band size.
This tool estimates your fit by rounding your underbust to the nearest even band and then mapping your bust difference to a cup letter. It is designed to be practical and easy to use for online shopping and first-time fitting.
How to measure correctly at home
1) Measure your underbust
Wrap a soft measuring tape snugly around your ribcage, directly under the bust. Keep it horizontal and firm, but not painfully tight.
2) Measure your full bust
Measure around the fullest part of your bust while standing naturally. Keep the tape flat and level across your back.
3) Enter both numbers in the calculator
Select inches or centimeters, input the values, and click calculate. You will get an estimated size plus sister sizes.
Understanding the result
- Estimated size: Your starting point (for example, 34C).
- Sister sizes: Similar cup volume with different band tension (for example, 32D and 36B).
- Fit note: A short guide based on your measurements to help with comfort and support.
Signs your bra may not fit well
- Band rides up in the back (often too loose).
- Straps dig into shoulders (band may not be doing enough support).
- Cups gap at top or wrinkle (cup may be too large or shape mismatch).
- Spillage over cup edge (cup may be too small).
- Center gore does not sit flat against chest (cup size or style may be off).
Best practices after you calculate
Try 2–3 nearby sizes, especially sister sizes. Different brands and bra styles can fit differently even with the same label. Balconette, plunge, full-coverage, and sports bras all shape and support differently.
Think of the calculator output as your starting size, not a strict rule. Comfort, shape match, and support are what matter most.
Frequently asked questions
Is this calculator accurate?
It is accurate enough for a strong starting point. Final fit depends on brand sizing, fabric stretch, and bra style.
Can I use this for sports bras?
Yes. Use the result as a baseline, then check the brand’s sports-bra chart and support level (light, medium, high impact).
Why do sister sizes matter?
They help when one size feels close but not perfect. If your band feels tight, go up a band and down a cup. If your band feels loose, do the reverse.
Disclaimer: This bra fit calculator is for educational and informational use. It does not replace an in-person professional fitting.