How to Measure Your Bra Band and Cup Size at Home
Two measurements, three minutes, and the cup-letter math. That's all you need for an accurate bra size — no fitter required.
The Two-Measurement Method
- Wear a non-padded bra or none. Padded bras add 0.5–1 inch to bust measurement.
- Measure underbust. Tape around ribcage directly under breasts, parallel to floor, snug not tight. Read on a normal exhale. The number in inches = band size.
- Measure bust. Tape around the fullest part of breasts, parallel to floor. Don't compress.
- Subtract underbust from bust. The difference = cup letter.
Cup letter math
Worked Examples
| Underbust | Bust | Diff | Cup | Final size |
|---|---|---|---|---|
| 30" | 33" | 3" | C | 30C |
| 32" | 34" | 2" | B | 32B |
| 32" | 36" | 4" | D | 32D |
| 34" | 37" | 3" | C | 34C |
| 34" | 39" | 5" | DD | 34DD |
| 36" | 39" | 3" | C | 36C |
| 36" | 42" | 6" | DDD/F | 36F |
| 38" | 44" | 6" | F | 38F |
| 40" | 47" | 7" | G | 40G |
The Band Is 80% of the Fit
Band-first principle
Try-on test: with arms raised overhead, the back of the band should stay level with the front. If it rides up 1+ inch, drop one band size and go up one cup letter (sister sizing — same volume, tighter band). See our sister-size guide.
Reading International Sizes
| US/UK | EU/IT | FR/ES | AU |
|---|---|---|---|
| 32A | 70A | 85A | 10A |
| 32B | 70B | 85B | 10B |
| 32C | 70C | 85C | 10C |
| 34A | 75A | 90A | 12A |
| 34B | 75B | 90B | 12B |
| 34C | 75C | 90C | 12C |
| 34D | 75D | 90D | 12D |
| 36C | 80C | 95C | 14C |
| 36D | 80D | 95D | 14D |
For full international bra conversions and sister sizing see our bra size chart.
Common Mistakes
Measuring with a padded bra
Adds 0.5–1 inch. Always measure with non-padded bra or none.
Pulling the tape tight to make underbust smaller
Causes a band that strangles you. Snug, not tight.
Compressing the bust measurement
Always let bust tape rest naturally at the fullest point.
Adding 4 to underbust for band
That's an outdated method. Modern brands use underbust directly.
FAQs
How do I measure my bra size at home?
Underbust = band. Bust − underbust = cup letter (1" = A, 2" = B, etc.).
Should I round band size up or down?
Round to nearest even number. Bands come in even sizes (30, 32, 34).
What's a typical bra size?
US average is 34DD. UK average is 36D.
Why does band feel different across brands?
Brands measure band stretch differently. Try sister sizing if rides up.
How often to remeasure?
Every 6 months, or after weight change/pregnancy.
Band or cup more important?
Band. ~80% of support comes from band.
Two Numbers, Right Bra
For full bra system reference see bra size chart; for cup-volume swaps see sister sizes; for activewear see sports bra measurement.
Selling lingerie on Shopify? Cut sizing returns.
Tailor Size Guide adds underbust + bust matching with sister-size suggestions to every bra listing.