Straight answers to what people actually ask us — about the tools, the math, and how private everything really is.
Yes — every calculator on this site is free, with no signup and no hidden tier. That's not changing.
No. Every calculator runs in your browser using JavaScript. Your numbers never leave your device or reach our servers.
It uses the standard band-and-cup method fitters have relied on for decades. It's an estimate based on two measurements — accurate for most people, but brand cuts vary, so treat the result as a strong starting point, not a guarantee.
Different sites use different rounding rules for the band. We use the modern method (round up to the nearest even inch) instead of the older +4 method — see our fitting process for the exact math.
A sister size is a different band/cup combination that holds roughly the same cup volume. Going up one band size and down one cup letter (or the reverse) usually fits similarly. Try the Sister Size Calculator.
Try the AI Smart Fit Calculator — it estimates your size from your dress size and how your current bra feels.
Because the same two measurements mean slightly different things depending on your situation — a teen's body is still changing, postpartum sizing shifts week to week, and older skin/tissue changes affect fit. Each version gives fit notes suited to that stage.
The underlying measurement is the same — only the band/cup labels differ by country. See Global Size Converter to convert your size to any of 7 systems at once.
Claire spent 10+ years hand-fitting women in specialty lingerie boutiques before building this site. She's not a doctor or clinician — she writes from real fitting-room experience. Read more on the About page.
No. These tools are for fit and shopping guidance only. See our full disclaimer.
Cut, fabric stretch, and each brand's own size chart all shift the fit. Try the Brand Size Decoder for a starting point at specific retailers.
Weight changes, pregnancy, and even a new season of exercise can shift your size. A quick remeasure every 6-12 months (or after a major body change) keeps you accurate.
Yes — the band and cup measurements work the same way regardless of underwire. Just size based on your closest supportive band.
No. This site is calculators and education only. Our Best Bras guides link out to retailers, but we don't sell anything ourselves.
It's on the roadmap — see Get the App for the honest status.
That's usually a shape or style issue, not a size issue. Check Fit Problems for the specific symptom.
The calculators themselves send nothing anywhere — see our Privacy Policy for the full picture, including standard hosting logs.
Yes — email us at hello@bra-sizecalculator.com. Reader requests have shaped a lot of what's on this site.