Bra Size Calculator
Enter your measurements to estimate a starting bra size (US/UK format).
Tip: This tool gives a starting point. Bra fit can vary by brand, style, and breast shape.
If you have ever wondered whether your bra size is correct, you are not alone. A large number of people wear the wrong size without realizing it, which can cause discomfort, poor support, and clothes that do not fit the way they should. This measure bra size calculator is designed to give you a quick, practical starting point using two simple measurements: your underbust and your full bust.
How this measure bra size calculator works
The calculator uses a straightforward approach:
- Band size is estimated by rounding your snug underbust measurement to the nearest even number.
- Cup size is estimated from the difference between your full bust and your calculated band size.
- Final size combines both values (for example, 34C).
This is a widely used sizing method for online size estimation and first-time fitting. It is especially useful when you are shopping online and need a baseline before trying different styles.
How to measure at home for better accuracy
1) Measure your underbust
Wrap a soft tape measure directly under your bust, around your ribcage. Keep it level all the way around your body and pull it snug (not painfully tight). Exhale naturally before reading the number.
2) Measure your full bust
Measure around the fullest part of your bust. Keep the tape flat and level, and avoid compressing breast tissue. If possible, stand straight in front of a mirror to keep the tape horizontal.
3) Re-check both measurements
Take each measurement twice and use the average if they differ. Small errors (even 0.5 in or 1 cm) can change cup estimation.
Cup difference quick reference
Most US/UK systems increase cup size about one step per inch of bust-to-band difference.
| Difference (inches) | Approx. Cup |
|---|---|
| 0 | AA |
| 1 | A |
| 2 | B |
| 3 | C |
| 4 | D |
| 5 | DD/E |
| 6 | DDD/F |
| 7 | G |
| 8 | H |
Understanding sister sizes
Even if the calculator suggests one size, nearby sizes can fit better depending on brand and bra style. Sister sizes keep cup volume similar while changing band tightness:
- Go down one band size (for example 34 to 32), then go up one cup (C to D).
- Go up one band size (34 to 36), then go down one cup (C to B).
This is useful if the cup feels right but the band is too tight or too loose.
Common bra fit mistakes
- Band riding up in back: usually means band is too loose.
- Straps digging in: often caused by too much weight on straps and not enough support from the band.
- Cup spillage: cups likely too small.
- Gaping cups: cups may be too large, or bra shape may not match your breast shape.
- Underwire sitting on tissue: cup size or wire shape may be incorrect.
Frequently asked questions
Is this calculator 100% exact?
No online tool can be perfect for every body type and bra brand. Think of this as a strong starting estimate.
Should I measure while wearing a bra?
For best consistency, measure over a thin, non-padded bra or without a bra. Avoid heavily padded bras when taking measurements.
How often should I re-measure?
Re-measure every 6-12 months, or anytime your weight, hormones, pregnancy status, or workout routine changes significantly.
Final tip
Use the result from this measure bra size calculator as your baseline, then test one or two sister sizes. Comfort, support, and shape are the real indicators of a great fit.