Bra Size Calculator
Enter your measurements below to get a practical starting bra size, plus sister sizes for easier shopping.
Tip: Use a soft tape measure and keep it level around your body. This is a starting point, not a final fitting.
How this bra measuring guide calculator works
This calculator gives you a practical starting bra size using two key ideas: your band size comes from your underbust measurement, and your cup size comes from the difference between your bust and band. If you provide multiple bust measurements (standing, leaning, and lying), the calculator averages them for a more balanced estimate.
Because bra brands, styles, and materials vary, no calculator can guarantee a perfect fit in one try. The goal here is to reduce guesswork so you can start with sizes that are much closer to your ideal fit.
Step-by-step measuring instructions
1) Get prepared
- Use a flexible measuring tape.
- Measure over a non-padded bra or thin bralette.
- Stand naturally with relaxed shoulders.
- Keep the tape parallel to the floor.
2) Measure your underbust
Wrap the tape directly under your bust, where your bra band sits.
- Snug underbust: firm but comfortable (required in calculator).
- Tight underbust: as tight as you can reasonably pull (optional, helps with band comfort range).
3) Measure your bust
Measure around the fullest part of your chest.
- Standing bust: normal upright position (required).
- Leaning bust: lean forward about 90 degrees (optional).
- Lying bust: lie flat on your back (optional).
If your standing and leaning measurements are very different, that usually means you benefit from trying a few cup options around the recommendation.
Understanding your calculator result
Band size
The calculator rounds your snug underbust to a standard even band size (for example 30, 32, 34, 36). Most support should come from the band, not the straps. A well-fitted band should feel secure on the loosest hook when the bra is new.
Cup size
Cup size is based on the difference between bust and band measurements. In general, each inch of difference increases cup volume by one step. Cup letters are not absolute across all band sizes; a 32D and 36D do not have the same cup volume.
Sister sizes
Sister sizes keep similar cup volume while changing band tension:
- Go down one band and up one cup (example: 34C → 32D).
- Go up one band and down one cup (example: 34C → 36B).
This is useful when your cup feels right but the band is either too tight or too loose.
Quick fit checklist after you try on a bra
- Band stays level and does not ride up in back.
- Center gore (middle panel) lies flat against your chest, if the bra style is designed for that.
- Cups contain tissue fully without spilling, wrinkling, or gaping.
- Underwire (if present) sits around breast tissue, not on it.
- Straps are supportive but not digging into shoulders.
Common bra sizing mistakes
Measuring over thick clothing
Bulky fabric can add extra centimeters or inches and push you into the wrong band and cup.
Starting with the wrong band strategy
If you only tighten straps to add support, your band may be too loose. A properly fitted band does most of the heavy lifting.
Ignoring brand and style differences
Plunge bras, balconettes, sports bras, and full-coverage styles can fit very differently. Treat your result as a starting size, then compare nearby sister sizes as needed.
When to remeasure
Recheck your measurements every 6 to 12 months, or anytime your body changes noticeably due to weight change, pregnancy/postpartum transitions, hormonal changes, medication, or major training shifts.
FAQ
Is this calculator US or UK sizing?
The cup progression used here follows a common US-style sequence with double-letter steps included. Some brands translate cup labels differently, so always check the brand chart.
What if I get a size I have never worn before?
That is very common. Many people have worn the wrong size for years because of inconsistent sizing standards across brands and stores. Try your result and the sister sizes before deciding.
Can I use centimeters instead of inches?
Yes. The calculator accepts centimeters and automatically converts to inches internally for cup-difference calculations, then gives clear results.
Note: This guide is educational and not a medical assessment. If you experience persistent discomfort, skin irritation, or pain, consider a professional fitting and medical advice.