Find Your Starting Bra Size
Enter all 6 measurements for a more accurate result. This calculator gives a starting size to try in fitting rooms.
How this bra that fits calculator works
This bra fitting calculator uses six body measurements to estimate two things: your band size and your cup size. The band comes from your snug ribcage measurement, while the cup is estimated from the difference between your bust volume and band size.
Unlike old “add 4 inches” methods, this approach starts with the size of your actual ribcage. That usually leads to a firmer, more supportive band and a cup that better matches breast volume. The final number and letter are a starting point, not a strict rule.
The 6 measurements you need
- Loose underbust: tape resting gently around your ribcage.
- Snug underbust: tape comfortably firm (this drives band size).
- Tight underbust: tape pulled as tight as tolerable.
- Standing bust: fullest part of bust while standing naturally.
- Leaning bust: fullest part while bending forward at 90°.
- Lying bust: fullest part while lying flat on your back.
Step-by-step measuring instructions
- Measure without a padded bra (or braless if comfortable).
- Exhale gently before underbust measurements.
- Keep the tape parallel to the floor all the way around.
- For bust measurements, do not compress breast tissue.
- Record to the nearest 0.5 cm or 0.25 inch for best accuracy.
- Repeat each measurement once to reduce random error.
Understanding band and cup size
A bra size has two parts, like 34F. The number is the band. The letter is cup volume relative to that band. That means cups are not absolute—34F is a different volume than 38F.
Sister sizes matter
If the band feels too tight but cups are right, go up one band and down one cup (for example, 32F → 34E in UK labeling). If the band feels too loose, do the reverse.
| Fit issue | Try this adjustment |
|---|---|
| Band too tight, cups okay | Band +2, Cup -1 step |
| Band too loose, cups okay | Band -2, Cup +1 step |
| Cups overflow | Go up 1–2 cup steps |
| Wrinkled cups | Go down 1 cup step or try another cup shape |
Common fitting problems (and quick fixes)
Straps dig into shoulders
Usually a sign the band is too loose or the cups are too small. The band should do most of the support work, not straps.
Center gore won’t tack
If the center panel floats away from your sternum, cups may be too small or the bra shape may not match your root width/projection.
Band rides up in back
Try a smaller band. A level, snug band is key for support and comfort.
Underwire sits on breast tissue
You may need a larger cup or a wider wire. Also ensure you “scoop and swoop” while putting the bra on.
UK vs US cup labels
Brands do not label cup letters the same way. Many fuller-bust brands use UK sizing. US labels often differ after DD.
- UK sequence: D, DD, E, F, FF, G, GG, H...
- US sequence: D, DD/E, DDD/F, G, H, I...
Always check the brand’s size chart and whether the site lists UK or US cups.
Final reminder
Your calculated size is a starting line, not a finish line. Different bras fit differently based on cup shape, wire width, fabric stretch, and brand grading. Try nearby sister sizes and prioritize comfort, support, and breast tissue containment over the label.