Quick Answer: Measure your band snug around your ribcage under your bust, then your bust across the fullest part. The difference between the two numbers determines your cup size — a 1″ difference is an A, 2″ is a B, and so on.
What You Need
A soft measuring tape and a well-fitting (or no) bra. Measure over bare skin or a thin, non-padded bra for the most accurate result. Avoid measuring over a padded or push-up bra — it will throw off both numbers.
Step 1: Measure Your Band
Wrap the tape directly under your bust, around your ribcage, keeping it level and snug — tight enough that it doesn’t slide, not so tight it digs in. Round to the nearest whole number. If the number is odd, round up to the nearest even number for standard sizing, or down for European sizing conventions.
Step 2: Measure Your Bust
Wrap the tape around the fullest part of your bust, keeping it parallel to the floor and not pulled tight. Let it sit naturally against your body.
Step 3: Find Your Cup Size
Subtract your band measurement from your bust measurement. The difference in inches maps to a cup letter:
| Difference | Cup Size |
|---|---|
| 1" | A |
| 2" | B |
| 3" | C |
| 4" | D |
| 5" | DD/E |
| 6" | DDD/F |
Common Measuring Mistakes
- Measuring over a padded bra, which inflates the bust number
- Pulling the band tape too tight, which shrinks the band number artificially
- Measuring bust while slouching, which reduces bust projection
- Rounding in the wrong direction consistently, which compounds error across both numbers
Why the Right Measuring Technique Matters
A measurement taken even slightly wrong compounds into the wrong size recommendation, which is why so many self-measuring guides produce inconsistent results. The two most common errors — pulling the band tape too tight and measuring bust while wearing a padded bra — both push you toward a smaller calculated size than you actually need, which is part of why band-too-big, cup-too-small remains the most common fit mistake industry-wide.
Measuring at Different Times of the Month
Breast tissue can fluctuate meaningfully across a menstrual cycle due to hormonal water retention, sometimes by half an inch or more in bust measurement. If your measurements seem inconsistent between attempts, try measuring at a consistent point in your cycle, and treat a single measurement as a strong starting point rather than a permanent number.
What to Do With Your Numbers
Once you have a band and cup calculation, that’s your starting size — not necessarily your final size. Try it in a familiar, well-reviewed style first. If the band rides up, the cup gaps, or straps dig in, use our Fit Troubleshooting guide to adjust from there rather than remeasuring repeatedly. Sizing is closer to a hypothesis you test than a fixed answer.
Frequently Asked Questions
Should I measure standing or sitting?
Standing, with relaxed posture — not pulled up straight, which can temporarily change your bust measurement.
Do I need someone to help me measure?
It’s easier with help for the band measurement, but entirely possible to do solo with practice, especially using a mirror.
Why does my calculated size not match what I usually wear?
Most people are wearing the wrong size already — this is extremely common. Try the calculated size first; if it feels off, check our Fit Troubleshooting guide.
