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Most People Wear the Wrong Bra Size
Bra fit is one of the hardest things to get right online — it's a big reason lingerie returns run high (see Why Lingerie Returns Are So High). A lot of the trouble comes from sizing myths: sticking to the size you think you are, ignoring sister sizes, and assuming every brand fits the same. Here's how to find your size properly.
Step 1 — Measure Your Band
Wearing an unpadded bra (or none), wrap a soft tape snugly around your ribcage directly under your bust, level all the way around. Round to the nearest whole number. This is your band size.
Step 2 — Measure Your Bust
Wrap the tape around the fullest part of your bust, keeping it level and not too tight. This is your bust measurement.
Step 3 — Calculate the Cup
Subtract your band from your bust measurement. The difference gives the cup:
- 1 inch ≈ A
- 2 inches ≈ B
- 3 inches ≈ C
- 4 inches ≈ D
- 5 inches ≈ DD/E
So a 34" band with a 37" bust (3" difference) ≈ 34C. (Use the cm equivalents if the brand lists centimeters.)
Step 4 — Understand Sister Sizes
This is the step most guides skip. A sister size has the same cup volume but a different band — e.g., 34C, 32D, and 36B hold a similar cup. If your calculated size feels off in the band, a sister size often fits better. Knowing them turns one rigid number into a small range you can fine-tune.
Step 5 — Check the Brand and Reviews
Bra sizing varies between brands just like everything else in fashion. Read reviews for "runs small in the band" or "cups run large," and check the brand's own size guide. The most effective help, though, is a direct recommendation: in one study, bra returns fell from 20% to 5% when shoppers followed a product recommendation instead of picking from a listing.
Where YourSizer Fits
When a store uses YourSizer, you don't have to second-guess band, cup, and sister sizes alone — you get a product-specific size answer based on you. Until then, measure carefully and keep your sister sizes handy.
Sources
Frequently Asked Questions
How do I measure my bra size at home?
Measure your band snugly under the bust, measure the fullest part of your bust, then subtract band from bust — each inch of difference is roughly one cup size.
What is a sister size?
A bra size with the same cup volume but a different band, e.g., 34C, 32D, and 36B. If your band feels off, a sister size often fits better.
Why do my bra returns keep happening?
Bra fit is precise and varies by brand, and sizing myths lead to wrong picks. A direct size recommendation has been shown to cut bra returns from 20% to 5%.