Bra Size Calculator (Inches)
Use this quick calculator to estimate your US bra size using inches. Measure with a soft tape and keep it level around your body.
Tip: This gives a starting size. Final comfort can vary by brand, bra style, and fabric stretch.
How to use a bra size calculator in inches
A good bra starts with good measurements. This bra size calculator inches tool uses two numbers: your underbust and your full bust. From there, it estimates your band size and cup size using a standard inch-based method.
If you have ever felt like your straps are digging in, your band rides up, or your cups gap, your current size may be off. Even a one-size adjustment can make a major difference in comfort and support.
Step 1: Measure your underbust
Wrap a soft measuring tape directly under your bust, where the band sits. Keep the tape snug and level all the way around. Breathe out normally and record the measurement in inches.
Step 2: Measure your full bust
Measure around the fullest part of your bust, again keeping the tape level. The tape should rest gently against your body without compressing breast tissue.
Step 3: Enter measurements and calculate
Input both values in the calculator above. The tool rounds to a practical band size and uses the bust-to-band difference to estimate cup letter.
How this calculator estimates cup size
In inch-based systems, cup size is often calculated from the difference between full bust and band size. A larger difference means a larger cup letter.
| Bust - Band Difference | Approx. US Cup |
|---|---|
| 0 in | AA |
| 1 in | A |
| 2 in | B |
| 3 in | C |
| 4 in | D |
| 5 in | DD / E |
| 6 in | DDD / F |
| 7 in | G |
| 8 in | H |
| 9 in | I |
| 10 in | J |
What are sister sizes?
Sister sizes are different size labels with similar cup volume. For example, if 34C feels too tight in the band, 36B may feel better while keeping similar cup volume. If 34C feels too loose in the band, 32D may be a better test.
- Band up (looser): go up one band size, down one cup letter.
- Band down (tighter): go down one band size, up one cup letter.
Common bra fit signs to watch for
- Band rides up in the back: likely band is too loose.
- Spillage at the top or sides: cups may be too small.
- Cup wrinkling or gaping: cups may be too large or shape mismatch.
- Straps doing all the work: band may not be providing enough support.
- Center gore does not tack: cup volume or wire shape may be off.
Best practices for more accurate results
Measure more than once
Take each measurement 2–3 times and average them. Small tape shifts can change your estimated cup size.
Use the same units throughout
This page is designed for inches only. Mixing inches and centimeters will give incorrect results.
Consider bra style differences
A plunge bra, sports bra, and balconette may fit differently even in the same size. Always test fit with the style you plan to wear most.
Frequently asked questions
Is this bra size calculator inches tool exact?
It is a strong starting point, not an absolute final answer. Brand grading, cup shape, wire width, and stretch can all influence final fit.
Why does the calculator size differ from my current bra label?
Many people wear an inherited or guessed size for years. Also, sizing can vary between brands, regions, and even bra models.
How often should I re-measure?
Re-check every 6–12 months, or sooner after body changes, pregnancy/postpartum, major training cycles, or significant weight changes.
Final takeaway
Using a bra size calculator in inches is one of the fastest ways to find a better fit baseline. Start with your measured size, test neighboring sister sizes, and prioritize comfort plus support over the label alone.