Official chart
Official ThirdLove size chartCompleted brand guide
ThirdLove Bra Size Guide
ThirdLove is built around a fit-first system: standard bra sizing, half-cup sizes for in-between cups, and a Fit Quiz for size and style recommendations. The brand says its bras are designed in AA-H cups, including half cups, and its older size-expansion article described bands from 30 to 48 and cups from AA to I.
The practical rule: use your normal US size as the anchor, but do not skip half cups if you are between sizes or repeatedly see cup gaping, edge digging, or uneven fullness.
Sizing system
ThirdLove's sizing system explained
Band, cup, and half-cup sizing
ThirdLove explains bra size as the usual band number plus cup letter, then adds half cups for people who fall between standard cup sizes. Its education page specifically says not to round measurements to a whole number because ThirdLove makes half-cup sizes.
Fit Quiz and style matching
ThirdLove recommends its Fitting Room/Fit Quiz when shoppers are not sure of size, and its measuring guide says breast shape and fit issues matter alongside tape measurements. That means the chart gives the starting label, while the quiz and style choice narrow the final bra.
Official chart values
ThirdLove band and cup range
ThirdLove's public size materials show band choices from 30 to 48 and cup choices from AA through I, with half-cup options in between several standard cups. Availability can vary by style, so use this as a range guide rather than a promise that every bra is stocked in every size.
Band range shown
Cup range shown
Wireless sizing
ThirdLove wireless and Precise Sizing
Some ThirdLove wireless bras use Precise Sizing instead of a normal band-and-cup picker. The Form Wireless Bra product page describes Precise Sizing as lettered sizing with scaled cup sizes for better comfort and fit.
XS-3X
Best for up to C 1/2 cups
XS+-XL+
Best for D-E 1/2 cups
XS++-XL++
Best for F-G cups
Review notes
How ThirdLove fits from real reviews
ThirdLove fit guide
ThirdLove's 2026 fit guide says the 24/7 Classic T-Shirt Bra runs true to size for most customers and that half cups help when standard cups gap or bind.
ThirdLove Form Wireless
The Form Wireless Bra page lists True to size, moderate coverage, built-in foam cups, adjustable straps, and back closure.
Good Housekeeping
Good Housekeeping named the 24/7 Classic T-Shirt Bra its best T-shirt bra in 2026 and called out half cups, size range, side smoothing, and a 60-day return policy.
The fit story is more nuanced than simply “runs small” or “runs large.” ThirdLove's own guide says the 24/7 Classic T-Shirt Bra runs true to size for most customers, and specifically frames half cups as the solution for shoppers between standard cups. Good Housekeeping's tested guide praises the size range and half-cup options, but also notes that the tested T-shirt bra did not retain its shape after stretching as well as some others.
Style notes
Style-by-style sizing notes
24/7 Classic T-Shirt Bra
Start with your measured US size and consider a half cup if the band is right but the cup edge gaps or cuts in. Good Housekeeping highlighted this style as a strong T-shirt bra option.
24/7 Classic Uplift Plunge
ThirdLove describes the Uplift Plunge as balancing coverage and cleavage for lower necklines. Check cup edge placement carefully if plunge bras usually gap near the top.
Form Wireless and Precise Sizing
Do not force a normal band-and-cup expectation onto every wireless style. Form Wireless uses XS-3X, plus, and double-plus sizing groups based on cup range.
In-between sizes
ThirdLove's strongest sizing difference is the half-cup system. If a normal C is too shallow and D is too roomy, a C 1/2 is the kind of step this brand is designed around.
Use your Wearavo size
How to convert your Wearavo size for ThirdLove
Use Wearavo to get your US starting size, then compare the band and cup to ThirdLove's chart. If your result is close but your fit issue is specifically cup gaping, cutting in, or one side being fuller, test the nearest half-cup option before changing the band. If you choose a wireless style with Precise Sizing, use ThirdLove's own size selector instead of guessing from S/M/L.
Sponsored shopping links
Shop ThirdLove bras
Disclosure: Wearavo may earn a commission if you buy through sponsored links. Check ThirdLove's current product chart, Fit Quiz, and return terms before ordering.
FAQ
Does ThirdLove run true to size?
ThirdLove's own 2026 fit guide says the 24/7 Classic T-Shirt Bra runs true to size for most customers. Still, the point of ThirdLove's system is that in-between fit issues may need a half-cup size rather than a normal full-cup jump.
What are ThirdLove half-cup sizes?
ThirdLove offers half-cup sizes such as A 1/2, B 1/2, C 1/2, D 1/2, and E 1/2. They are intended for people who feel caught between standard cup sizes.
What is my size in ThirdLove?
Start with your measured US band-and-cup size, then compare it with ThirdLove's own chart and Fit Quiz. If your usual cup gaps or digs but the band feels right, a half cup may be the next size to test.
Does ThirdLove use normal bra sizes?
For many bras, yes: ThirdLove uses standard US-style band-and-cup labels, with added half cups. For some wireless bras, ThirdLove uses Precise Sizing with XS-3X, plus, and double-plus size groups.
What is ThirdLove's return or exchange policy?
The Form Wireless product page states a Perfect Fit Promise with free exchanges for 60 days on eligible orders, with tags and packaging requirements and final-sale exclusions. Check the current product page before ordering.
Is ThirdLove good for T-shirt bras?
Good Housekeeping named the ThirdLove 24/7 Classic T-Shirt Bra its best T-shirt bra in a 2026 tested guide, noting the wide size range, half-cup options, side smoothing panels, and 60-day return period.
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