How to Measure for a Knix Bra Size
Two measurements, under 3 minutes. Find your standard size, then match it to the right Knix system — WingWoman uses bands 28–48; wireless styles use Knix's alpha-plus scale.
Verified Jun 2026 · Source: Knix official size guide ↗
Knix Bra Size Calculator
Enter your band and bust measurements for your standard band-and-cup size — use it directly for the WingWoman, or convert it on Knix's site for alpha-plus styles.
Measure snugly around your ribcage (underbust) and at the fullest part of your bust.
Where to place the tape
Band sits level around your rib cage just under the bust. Bust wraps the fullest point.
Measure your bust
Wrap a tape around the fullest part of your bust. Keep it level and not too tight.
Measure your underbust
Wrap the tape snugly around your ribcage, just below your breasts. Keep it level.
Enter your measurements
Use our calculator to get your size in US, UK, EU, and AU systems with sister sizes.
How to Measure for a Knix Bra: Step by Step
Wear a non-padded bra
Put on a regular T-shirt bra or unlined bralette — not a push-up, sports bra, or minimizer. Padded styles add volume and skew your bust measurement.
Tip: If you can see the shape of your natural bust in the mirror, you're ready to measure.
Measure your band (underbust)
Wrap a soft tape measure snugly around your rib cage directly under your bust, level all the way around. Knix uses your underbust measurement directly — no inches added — and says to round up to the next even number if you land on an odd or fractional number.
Tip: The tape should feel firm but not tight — you should be able to breathe normally.
Measure your bust
Wrap the tape around the fullest part of your bust. If you are fuller at the bottom, lean forward from the waist to measure the fullest point. Keep the tape level. Round to the nearest whole inch.
Tip: Look in a mirror from the side to confirm the tape isn't dipping or riding up.
Calculate your standard cup size
Subtract your band from your bust. Each inch of difference equals one cup size: 1 inch = A, 2 = B, 3 = C, 4 = D, 5 = DD, 6 = DDD. Knix uses this same standard math — their own example: a 38-inch bust minus a 34-inch band is 4 inches, a D cup, so 34D.
Tip: Example: 38-inch bust minus 34-inch band = 4 inches = D cup → 34D.
Match it to the right Knix system
Knix uses two systems. For the WingWoman Contour Bra, use your standard band-and-cup size directly (it comes in bands 28–48, cups A–H). For most wireless, everyday, and sports styles, Knix uses its own alpha-plus scale (XS, S+, M++, and so on) — enter your standard size or measurements into Knix’s on-site size guide and it returns your alpha-plus code.
Tip: The older Evolution 1–8 number system has been retired — ignore any 1–8 charts you find elsewhere.
Verify with sister sizes if the fit feels off
On standard band-and-cup styles, try a sister size if the band feels wrong: go down one band and up one cup (34D → 32DD) for a tighter band, or up one band and down one cup (34D → 36C) for more room. The cup volume stays the same.
Tip: Both directions hold the same amount of breast tissue — only the band fit changes.
Knix's Two Sizing Systems, Explained
This is the part that trips people up. The WingWoman Contour Bra uses standard US band-and-cup sizing — bands 28 to 48, cups A through H — so your measured size is your size. Most other Knix styles use the brand’s own alpha-plus scale (XS through XXXXL++), where the letter maps to the band and the plus signs add cup depth; for those, you enter your size or measurements into Knix’s on-site guide to get the code. The old Evolution 1–8 number system has been retired, so ignore any 1–8 conversion charts still floating around.
Do Knix Bras Run True to Size?
Yes — Knix runs true to size. Because the bras are wireless, the band often feels snug for the first few wears and washes, then relaxes to its final fit. Don’t size up on day one; give a new Knix bra a few days first. If after that the band is genuinely too tight or too loose, a sister size on standard band-and-cup styles is the fix, not a different cup volume.
What If Your Size Doesn't Fit?
On standard band-and-cup styles like the WingWoman, sister sizes share cup volume but shift the band. Band too tight? Go up a band and down a cup (34D → 36C). Cup overflowing? Go down a band and up a cup (34D → 32DD). On alpha-plus styles, try the next plus level up or down rather than a different letter.
Next steps
Got your size? Compare it against Knix's full chart, or check the fit checklist to make sure your bra is working as hard as you are.
Also see: how a well-fitting bra should feel · signs you're wearing the wrong bra size · bra fit troubleshooter
Measuring for another brand?
The band-and-bust method is the same across brands — only the size range and style notes differ. Brand-specific measuring guides: