# Sports Bra Size Guide: How to Measure for the Perfect Fit > Measure sports bra band and cup fit, compare support levels, and understand selected CRZ and 90 Degree By Reflex alternatives without assuming size equivalence. - Source: https://flexwearlab.com/activewear/sports-bra-size-guide - Publisher: FlexWearLab (https://flexwearlab.com) - Published: 2026-03-21 · Updated: 2026-10-19 - Category: activewear - Tags: sports bra sizing, how to measure, fitness apparel, activewear guide, bra fitting ## Quick answer Measure snugly around your ribcage under the bust and round up to an even number for your band. Subtract that ribcage measurement from your fullest bust measurement: each inch is one cup letter. Then check the fit: the band does 80 to 90 percent of the support, sits level and takes two fingers underneath. ## Buying routes Channel labels describe destinations, not a guarantee of current stock. Use the source page for current shopping links. ### Start with these options - **Nike Dri-FIT Swoosh Medium-Support Sports Bra** — Amazon product listing; channel: amazon. [Model and fit details](https://flexwearlab.com/activewear/sports-bra-size-guide#product-B0C4B35G9J). - Trade-off: Runs slightly small in band - **Under Armour Infinity High Sports Bra** — Amazon product listing; channel: amazon. [Model and fit details](https://flexwearlab.com/activewear/sports-bra-size-guide#product-B0C12Q3L89). - Trade-off: Higher price point ## Key takeaways - Band size is your ribcage measurement under the bust, rounded up to an even number; bust minus ribcage in inches gives the cup letter. - Some brand charts add 4 or 5 inches to the band; follow the brand's own chart where it has one. - The band should do 80 to 90 percent of the support: level all the way round, two fingers underneath, no riding up. - If a high-impact bra's band rides up, go down a band and up a cup (a sister size). - Under Armour Infinity High is the high-impact pick; Nike Dri-FIT Swoosh covers yoga, Pilates and light gym work. - Re-measure every 6 to 12 months and replace a bra after roughly 30 to 40 washes. ## Products reviewed 1. **Nike Dri-FIT Swoosh Medium-Support Sports Bra** (rated 4.5/5, details: https://flexwearlab.com/activewear/sports-bra-size-guide#product-B0C4B35G9J) — A reliable medium-support option ideal for yoga, Pilates, and light gym workouts with excellent moisture management. - Shopping: Product page; check current size, seller and availability on Amazon - Pros: Moisture-wicking Dri-FIT technology; Adjustable straps for custom fit; Wide bottom band for comfort; Available in extended sizes - Cons: Runs slightly small in band; Limited color options in larger sizes; Padding not removable 2. **Under Armour Infinity High Sports Bra** (rated 4.7/5, details: https://flexwearlab.com/activewear/sports-bra-size-guide#product-B0C12Q3L89) — Top-tier high-impact support that's worth the investment for serious athletes and runners. - Shopping: Product page; check current size, seller and availability on Amazon - Pros: High-impact support for running and HIIT; HeatGear fabric keeps you cool; Racerback design for range of motion; Quick-dry material - Cons: Higher price point; Can feel tight initially; Hand wash recommended 3. **90 Degree By Reflex Long Line Racerback Sports Bra** (Manufacturer information · not tested, details: https://flexwearlab.com/activewear/sports-bra-size-guide#product-B09P45ZJ5C) — Different brand replaces the Lululemon Energy Long Line in this general fit guide only. Alpha sizing replaces Lululemon numbered sizing; strap adjustability and equivalent cup coverage are not established. Selected from listing details; not independently tested. - Shopping: Product page; check current size, seller and availability on Amazon - Selected listing: Selected replacement: Black, X-Large, medium-impact longline racerback. Different brand replaces the Lululemon Energy Long Line in this general fit guide only. Alpha sizing replaces Lululemon numbered sizing; strap adjustability and equivalent cup coverage are not established. Seller at the October 19, 2026 check: 90 Degree By Reflex. Stock was confirmed for this selection only; check your size, current seller and return terms on Amazon. This replacement is listing-based and has not been wear-tested by us. - Pros: Listed medium-impact longline design; Racerback layout - Cons: XL selected; other sizes unverified; No established adjustable straps or matching Lululemon cup coverage 4. **CRZ YOGA Butterluxe Y Back Sports Bra — True Navy** (Manufacturer information · not tested, details: https://flexwearlab.com/activewear/sports-bra-size-guide#product-B0B7RVV96V) — True Navy Small CRZ Butterluxe Y Back is a light-support yoga bra with removable pads. It is not Lululemon Nulu or the Gymshark seamless bra, and neither numbered sizes nor previous inversion-security and support results transfer. Listing-based, unrated and not independently tested. - Shopping: Product page; check current size, seller and availability on Amazon - Selected listing: Selected listing: True Navy, Small. True Navy Small CRZ Butterluxe Y Back is a light-support yoga bra with removable pads. It is not Lululemon Nulu or the Gymshark seamless bra, and neither numbered sizes nor previous inversion-security and support results transfer. Seller at the October 19, 2026 check: CRZ YOGA. Stock applies only to this selection. Check measurements, current seller and return terms. Listing-based; not independently wear-tested. - Pros: Light support and removable pads; Scoop neck and spaghetti-strap Y back - Cons: Selected variant only; check measurements and current seller; Listing-based alternative; not wear-tested here Listing checks are point-in-time observations, not a guarantee of current stock or brand authorization. Follow the source page for current shopping links and check your size, color, seller and delivery location. Measure snugly under your bust for the band, subtract that from your fullest bust measurement for the cup, then let the fit checks overrule the number: a band that rides up is too big, whatever the tag says. You need a soft tape measure, a mirror and about five minutes, and the steps below also cover how much support each kind of workout needs. **Selection update — October 19, 2026:** New alternatives on this page use manufacturer/listing evidence. Earlier testing describes the original models only; no old rating, fit result or measured performance transfers to a replacement. **Availability checked October 19, 2026.** The replacements below are selected from listing details, not our earlier wear tests. Stock applies only to the linked color and size; check your own size, current seller and return terms. A sports bra that fits badly rides up, digs in, chafes and lets you bounce. Measuring gets you a starting size; the fit checks below tell you whether a particular bra actually works. *Related: [Best Running Shorts for Women in 2026: Tested Across Every Distance](https://flexwearlab.com/activewear/best-running-shorts-women-2026).* ## Why fit matters more in a sports bra A sports bra has a different job from an everyday bra: it has to control movement while you run, jump and twist. The more movement it allows, the more uncomfortable the workout, and for many women that bounce is painful. Fit decides how well it controls that movement, whatever your cup size, though larger busts need more structure. The usual signs of a poor fit: - Straps that dig in, a band that rides up, or spilling over the cups - Rubbing and chafing where the band or straps move against skin - Adjusting the bra mid-workout, or not being able to lift your arms freely ## The three sizing systems Sports bras are sold in one of three ways, and it's worth knowing which one you're buying. ### Band and cup (34B, 38DD) The same system as everyday bras: a number for the band in inches and a letter for the cup. It gives the most precise fit and is common in medium- and high-support styles. ### Alpha (XS to XL) Common on compression bras. It's simpler and less precise, and it works best for smaller cups (roughly A to C) and low- to medium-impact work. Some brands extend it from XXS to 3XL. ### Combined ranges Some brands map each letter size to a range, for example S for 32A-34B or L for 36C-38D. Convenient, but a range can't fit as closely as a band-and-cup size. ## How to measure Measure in an unpadded bra that fits well, or no bra. A second person holding the tape helps. ### Step 1: Your band The band does most of the supporting, so this is the measurement that matters most. 1. Stand straight with your arms relaxed. 2. Wrap the tape snugly around your ribcage, directly under your bust. 3. Check in the mirror that it's level all the way round. 4. Breathe out fully and read the measurement. 5. Round to the nearest whole inch. If it's an odd number, round up to the next even number: that's your band size. Some brand charts still use an older method that adds 4 or 5 inches to this number. If the brand you're buying publishes its own chart, follow it; if not, use your ribcage measurement as above and let the fit checks decide. ### Step 2: Your bust 1. Stand straight with your arms relaxed. 2. Wrap the tape around the fullest part of your bust. 3. Keep it level and snug but not tight. 4. Round to the nearest whole inch. ### Step 3: Your cup Subtract your ribcage measurement from your bust measurement. Each inch of difference is one cup letter: | Difference | Cup Size | |------------|----------| | 1 inch | A | | 2 inches | B | | 3 inches | C | | 4 inches | D | | 5 inches | DD/E | | 6 inches | DDD/F | | 7 inches | G | | 8 inches | H | For example, a 32-inch ribcage and a 37-inch bust is a 5-inch difference, so 32DD. ### Step 4: Check the fit Your measurements are a starting point, and fit varies between brands and styles. Try the bra on if you can and check three things. The band should be snug but let you breathe, sit level all the way round without riding up at the back, and let two fingers slide underneath, no more. The cups should hold all of you with no spilling over the top or sides and no gaping or wrinkling. The center panel between the cups should lie flat on your breastbone. The straps should stay put without digging in, take two fingers underneath, and not slip off or leave marks. ## Support level by activity The harder the activity, the more support you need and the more exact the fit has to be. ### Low impact Yoga, Pilates, walking, weight training. Low-impact bras give light compression and often have no molded cups. Sizing is forgiving, and many women like them a little looser for bending and stretching. ### Medium impact Cycling, hiking, moderate gym sessions, dance classes. These combine compression with separate cups (encapsulation), usually come in band-and-cup sizes and sometimes have underwire or structured cups. Wear them snugger than a low-impact bra, but comfortable enough for a long session. ### High impact Running, HIIT, jumping, boxing, hard cardio. These need the most exact fit and usually combine compression, encapsulation and reinforced construction. The band should be firm and do 80 to 90 percent of the supporting, with wide, possibly padded straps to spread the load. If a high-impact bra's band rides up when you jump, go down a band size (and up a cup to keep the same volume). A tighter band stays down. ## Where sizing goes wrong ### Wearing the same size for years Weight changes, hormones, pregnancy and age all change your size. Re-measure every 6 to 12 months, or whenever your bras start to feel wrong. ### Ignoring sister sizes A sister size has the same cup volume on a different band. If your size isn't available or doesn't quite fit, try one: | Your Size | Sister Size Down | Sister Size Up | |-----------|------------------|----------------| | 34C | 32D | 36B | | 36D | 34DD | 38C | | 38DD | 36DDD | 40D | Down a band and up a cup keeps the volume with a firmer band. Up a band and down a cup keeps the volume with a looser one. ### Buying for looks A bra you love the look of but that doesn't fit won't support you. For high-impact work especially, fit comes first. ### Assuming brands match A 34C from Nike can fit differently from a 34C from Lululemon. Check each brand's own size chart and read fit comments in reviews before you buy. Even the measuring can differ: Nike's [sports bra size chart](https://www.nike.com/size-fit/womens-bras) measures the bust from the center of the chest to where breast tissue ends on one side, not all the way round, and converts that to its own alpha sizes. ## Four bras by activity | Feature | Nike Dri-FIT Swoosh | Under Armour Infinity High | 90 Degree By Reflex Long Line Racerback Sports Bra | CRZ YOGA Butterluxe Y Back Sports Bra — True Navy | |---------|---------------------|---------------------------|--------------------------|---------------| | Support Level | Medium | High | Medium (listed) | Light (listed) | | Sizing System | Traditional | Traditional | Alpha; selected XL | Alpha; selected Small | | Best For | Yoga, Pilates | Running, HIIT | Studio workouts; fit check required | Yoga after fit check | | Extended Sizes | Yes (up to 44G) | Yes (up to 42DD) | Other sizes not verified | Other sizes not checked | | Adjustable Straps | Yes | No | Not established | Not established | ### Nike Dri-FIT Swoosh Medium-Support Sports Bra Medium support with good sweat-wicking, for yoga, Pilates, heated classes and moderate gym work. The straps adjust and the wide underband spreads pressure. It comes in extended sizes up to 44G. The band runs slightly small, so size up if you're between sizes. ### Under Armour Infinity High Sports Bra The high-impact pick, for running and HIIT. The racerback leaves your arms free while holding everything in place, and the HeatGear fabric dries quickly, so it doesn't turn soggy on a long sweaty session. It costs more than the others here. It feels tight at first and eases as you wear it. ### 90 Degree By Reflex Long Line Racerback Sports Bra — available replacement The [90 Degree By Reflex Long Line Racerback Sports Bra](https://flexwearlab.com/activewear/sports-bra-size-guide#product-B09P45ZJ5C) is the available replacement. Different brand replaces the Lululemon Energy Long Line in this general fit guide only. Alpha sizing replaces Lululemon numbered sizing; strap adjustability and equivalent cup coverage are not established. The listing describes medium-impact support, stretch fabric and a longline racerback. Compare bust and underbust measurements with this brand's chart; an XL selection is not evidence that it fits every bust shape. This is a listing-based studio option, not a verified running bra. ### CRZ YOGA Butterluxe Y Back Sports Bra — True Navy — selected alternative The [CRZ YOGA Butterluxe Y Back Sports Bra — True Navy](https://flexwearlab.com/activewear/sports-bra-size-guide#product-B0B7RVV96V) is a selected alternative to Gymshark Seamless Racerback Sports Bra. **Selected variant:** True Navy, Small. **Model and specification differences:** True Navy Small CRZ Butterluxe Y Back is a light-support yoga bra with removable pads. It is not Lululemon Nulu or the Gymshark seamless bra, and neither numbered sizes nor previous inversion-security and support results transfer. The listing describes a scoop neck, spaghetti-strap racerback and A–D cup/26–33-inch underbust product guidance; use the selected size chart rather than treating that range as Small measurements. **Offer checked October 19, 2026:** CRZ YOGA. Availability applies only to this selected variant. This replacement is unrated and has not been independently wear-tested here. ## Fit by bust size and shape ### DD cup and above Look for a bra that combines compression and encapsulation, with: - Wide, cushioned straps to spread the weight - A firm band that does most of the supporting - Underwire or structured cups - Full coverage so nothing spills - A brand that specializes in larger sizes, such as Panache, Freya or Wacoal ### A and B cups You have more choice. Compression styles in alpha sizes usually work, racerbacks give enough support without underwire, and lighter construction is more comfortable on long sessions. Many can double as crop tops. ### Uneven breasts Having one breast larger than the other is common. Size your cup to the larger side, choose stretchy fabric that adapts, and consider lightly padded cups to even things out. Molded cups tend to gap on the smaller side. ## When to replace a sports bra Replace it when: - The band rides up at the back - The straps keep slipping or digging in - The elastic feels stretched - The fabric pills or thins - You feel more movement than you used to - It's 6 to 12 months old and in regular use Most sports bras keep their support for roughly 30 to 40 washes. Rotating three or four bras spreads that wear out. Whatever your measurements say, try more than one size and style where you can. Fit varies between brands, models and even colors of the same bra, and the fit checks above are the final word. ## Frequently Asked Questions ### Should a sports bra be tighter than a regular bra? Yes, in the band. A sports bra band should be snug enough that only two fingers slide underneath, and for high-impact work it should feel firm, because the band does most of the supporting. The straps and cups should still let you breathe and lift your arms freely. ### Is my sports bra size the same as my everyday bra size? It is a starting point, not a guarantee. Band-and-cup sports bras use the same system as everyday bras, but many compression bras use alpha sizes such as S or M, and brands measure differently, so check the brand's own chart and then do the fit checks. ### How do I know if my sports bra is too big? The band rides up at the back, the cups gape or wrinkle, the straps slip, or you feel more bounce than you should. Try a smaller band first; if the cups then feel tight, go to the sister size a band down and a cup up. ### What should I do if I am between sports bra sizes? For running and other high-impact work, choose the firmer band, since a tighter band stays down. For yoga and other low-impact work, many women prefer the looser of the two for bending and stretching. *Prices and availability change; check Amazon for current details. As an Amazon Associate, FlexWearLab earns from qualifying purchases.* --- Cite as: FlexWearLab, "Sports Bra Size Guide: How to Measure for the Perfect Fit", https://flexwearlab.com/activewear/sports-bra-size-guide. As an Amazon Associate I earn from qualifying purchases.