Bra Size Calculator
Select Simple to get a quick recommendation with 2 measurements, or switch to Advanced for precise sizing, sister sizes, and shape‑based style tips.
What is a bra size
A bra size is a band number plus a cup letter that together describe ribcage fit and breast volume.
How to measure for a bra
Use a soft tape and stand relaxed. Measure snug underbust for band and measure bust over the fullest point for cup.
- Keep the tape level around the body and close to the skin.
- Exhale gently when measuring the underbust for accuracy.
- Take standing, leaning, and lying bust measurements if using Advanced mode.
What the bra calculator does
The calculator rounds bands to retail sizes, maps cup volume by system, shows sister sizes, and suggests styles based on shape inputs.
Signs your bra fits
A good fit feels secure without pain and looks smooth under clothing.
- Band sits level and firm on the loosest hooks when new.
- Gore rests comfortably on the sternum without lifting.
- No quad boob at the top edge and no gaping at the cup.
- Straps do not dig in and do not carry the band load.
When to try a sister size
You should try a sister size when the band or cup is close but not quite right.
- If the band feels tight and the cups are correct, go up one band and down one cup.
- If the band feels loose and the cups are correct, go down one band and up one cup.
International size differences
US and UK use inch based cup steps while EU and JP use centimetre steps. FR and ES band labels are EU plus fifteen and IT labels are EU minus five.
Shape and style tips
Choose styles that match fullness, root width, and projection for comfort and shape.
- Full on top often prefers balconette or plunge to avoid cutting at the top edge.
- Full on bottom often prefers three part cups or stretch lace to fill the top edge.
- Narrow roots often prefer deeper cups and narrower wires.
- Shallow shapes often prefer molded T shirt cups or shallower demi cups.
Common mistakes to avoid
A few small adjustments improve comfort and support.
- Do not size up the band to fix cup spillage. Choose the correct cup volume first.
- Do not rely on straps for lift. The band should do most of the work.
- Replace worn bands that you can pull more than two inches from the back.
Bra size calculator FAQs
How do I calculate my bra size?
Measure snug underbust for band, measure bust at the fullest point for cup, and let the calculator map these to your chosen system.
What is a sister size?
A sister size keeps cup volume the same while changing the band. Up one band and down one cup or down one band and up one cup.
Why are my cups gaping?
The cup may be too large or the cup shape may be too shallow for your fullness. Try a smaller cup or a style with stretch lace.
Why do I get spillage at the top edge?
The cup is likely too small or your shape is full on top. Try one cup up or a balconette or plunge edge.
How tight should the band be?
The band should feel firm on the loosest hooks, sit level around the body, and not ride up during movement.
Can I use centimetres and get US UK sizes?
Yes. Choose centimetres for input and select US UK as the sizing system. The tool converts automatically.