Grabbing a tape measure is the easy part — knowing exactly where to wrap it, and how snug to pull it, is what actually determines whether the number you end up with is useful. Here's the short version, plus a video walkthrough if you'd rather watch than read.
Video: “How To Measure Your Bra Size - Tutorial” · hosted on YouTube.
The two measurements that matter
Every bra size, in every system, comes down to two numbers: your underbust (the band) and your bust (the fullest point). The gap between them is what determines your cup letter — everything else is just presentation.
Underbust, wrapped snug
Directly beneath the bust, tape level front and back, snug but not compressed. This becomes your band number.
Bust, wrapped loose
Around the fullest point, resting rather than pulling. This becomes your bust number.
Subtract the two
Bust minus underbust, in inches, gives your cup index — feed both into the bra size calculator for an instant result.
Getting it right
Three things people usually get wrong
Measuring over a padded bra
Padding inflates the bust reading specifically, throwing off your cup result.
Pulling the band too tight
Snug is the goal — you should still slide two fingers underneath comfortably.
Letting the tape ride up
Check a mirror to make sure the tape stays level all the way around.
Questions
Measuring FAQs
No — both measurements can be taken solo in front of a mirror, though a second pair of hands can help keep the tape level.
Roughly every 6 to 12 months, and sooner after any significant weight change, pregnancy, nursing, or surgery.
Round both to the nearest whole number and re-check — a half-inch of tape slack is a common cause of an inconsistent reading.
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