A sports bra fits when the band sits level and snug with about two fingers of room, the straps lie flat, the cups hold everything without creases or spillover, and nothing shifts when you jump. If the band rides up, the straps leave grooves or you bounce out of the top, the size or the style is wrong, and no amount of tugging will fix it.
This guide gives you a five-point fit check you can run in a fitting room or at home in about a minute, then shows exactly how the FIERCEPULSE sports bra is sized, using the measurements from our live size chart.
A sports bra is a bra built to hold the breasts steady during exercise, usually with a wide band, wider straps and stretch fabric that moves with you. The underband is the elastic band that runs around your ribcage directly under the breasts, and it does most of the holding. Underbust is the measurement taken right under your breasts, where the band sits, and it is the number that decides your size.
Key takeaways: the one-minute fit check
- ☐ Band: level all the way around, snug, about two fingers of room, never riding up your back.
- ☐ Straps: flat on the shoulders, no red grooves, and not doing the band's job.
- ☐ Cups and coverage: all breast tissue inside, no spillover at the top or sides, no wrinkles or gaps.
- ☐ Jump test: jump, jog in place and swing your arms; nothing should pinch, slip or bounce loose.
- ☐ After-wash re-check: repeat the band and strap checks after the first few washes.
How should a sports bra fit? The 5-point check
A well-fitting sports bra passes all five checks below in order: band first, because a wrong band throws off everything above it. On's fit guide puts it plainly: the band "should sit firmly (but comfortably) just below your bust and lie flat against your ribcage without digging in" (On, How a sports bra should fit). Shock Absorber's fitting guide gives the quick gauge most fitters use: you should be able to fit two fingers between the underband and your skin (Shock Absorber fitting guide on SportsShoes.com).
| Check | A good fit | Sign it is wrong | What to do |
|---|---|---|---|
| 1. Band | Level front to back, snug, two fingers of room, you can breathe deeply. | Rides up your back, or leaves deep red marks. | Riding up: size down. Digging in: size up. |
| 2. Straps | Flat on the shoulders, holding gently. | Grooves in your shoulders, or straps sliding off. | Re-check the band first; it is usually the real problem. |
| 3. Cups and coverage | All breast tissue inside, smooth fabric, neckline and armholes lie flat. | Spillover at the top or sides, or wrinkles and gaps. | Spillover: more room. Wrinkles: less room. |
| 4. Jump test | You feel held and secure while you jump and swing your arms. | Bouncing, pinching, or a band that creeps up. | Try the next size, or a style built for more hold. |
| 5. After-wash re-check | The band still passes the two-finger test after a few washes. | The band feels looser, or the bra shifts in the jump test. | Follow the care label and repeat checks 1 and 4. |
1. The band: snug, level and two fingers of room
The band should feel like a firm, even hug around your ribs, and it should sit at the same height in front and behind. Look in a mirror from the side. For example, if the back of the band sits higher than the front, the band is too loose and is being pulled up by the straps. If you cannot slide two fingers underneath or cannot take a full, deep breath, it is too tight.
2. The straps: flat, steady, and not doing all the work
Straps that dig in or slip are usually a band problem, not a strap problem. On's guide says straps "shouldn't be doing all the work," and that digging or slipping means "the fit's off somewhere else (likely the band)" (On). Shock Absorber suggests adjustable straps should sit securely on the shoulders with only one to two inch give (Shock Absorber fitting guide).
3. The cups and coverage: everything in, nothing wrinkled
Shock Absorber's rule is that the cup should contain the whole of the breast with no creases, and that gaping or wrinkling fabric suggests the cup is too big (Shock Absorber fitting guide). Check the sides under your arms as well as the neckline, because that is where tissue escapes first in a bra that is too small.
4. The jump test: move like you will in class
Standing still tells you about comfort, while moving tells you about fit. On's guide recommends you "Jump, jog, swing your arms" and feel for pinching, slipping or a band that rides up (On). Do ten jumping jacks in the fitting room, then reach forward as if you were on a spin bike or a reformer.
5. The after-wash re-check: the step almost nobody does
Fit is not a one-time verdict, so run checks 1 and 4 again after the first few washes. Stretch fabric settles with wear and laundering, and a band that was right on day one can loosen enough to start riding up. Ten seconds in front of a mirror after laundry day tells you whether your bra is still doing its job.
Why fit matters more than the size on the tag
Most women are not wearing the size that fits them, which is why a fit check beats a size label. The University of Portsmouth's Research Group in Breast Health studies how breasts move during exercise. It reports that over 80% of women have been reported to be wearing the wrong size bra, and its advice is to "search for your fit, not your size" (University of Portsmouth Research Group in Breast Health).
Fit is a comfort issue and a performance issue too. The same Portsmouth group found that 51.5% of the 1,659 women it surveyed experience breast pain (University of Portsmouth). Its research also links poorly supported breasts to a 4 cm shorter stride and to exercise that feels harder, which is the opposite of what you want from workout gear.
"Search for your fit, not your size."
University of Portsmouth Research Group in Breast Health
How to measure for a FIERCEPULSE sports bra
Our sports bras come in six sizes, XS to 2XL, and your underbust measurement picks the size. Keep the tape parallel to the floor for both measurements, which is how our size chart is built:
- Underbust: wrap the tape around your body right under your breasts, where the bra band sits.
- Chest: start at the fullest part of your chest and bring the tape around your back, under the armpits and over the shoulder blades, to where you started.
| Size | Underbust (in) | Underbust (cm) | Chest (in) | Chest (cm) |
|---|---|---|---|---|
| XS | 28 3/4 | 73 | 33 1/8 | 84 |
| S | 29 1/2 | 75 | 34 5/8 | 88 |
| M | 30 1/4 | 77 | 36 1/4 | 92 |
| L | 31 7/8 | 81 | 39 3/8 | 100 |
| XL | 33 1/2 | 85 | 42 1/2 | 108 |
| 2XL | 35 | 89 | 45 5/8 | 116 |
Body measurements from the FIERCEPULSE sports bra size chart on the product page, read November 6, 2026.
Our finding from the chart: from XS to M, each size step adds only 3/4 inch at the underbust. For example, a 30-inch underbust lands between S and M. From M to 2XL the underbust steps widen to about 1 1/2 to 1 5/8 inch, while the chest column grows by 3 1/8 inch per size. That means small measuring errors matter most in the XS to M range: measure twice, use your chest number as the tiebreaker, and when you still land between two sizes, follow the chart's own advice and order the size up. The chart also notes that finished bra measurements can vary by up to 1 inch, because every bra is made to order.
What our sports bra cut means for your fit
The FIERCEPULSE sports bra is a pull-on racerback with no hooks and no strap sliders, so the size you order is the fit you get. That makes the band check more important than usual: there is no extra hook to move to if the band feels loose, and no slider to shorten if the straps feel long. Here is what the product page lists for the cut:
- Scoop neckline and racerback.
- Support material in the shoulder straps, a double-layered front, and a wide elastic band under the bust.
- Flat seams and bias binding that minimize rubbing.
- Moisture-wicking, four-way stretch fabric.
- Best for A to C cups.
The product page describes the fabric as staying dry during low and medium intensity workouts. If you wear a D cup or larger, or you need a bra for running and jump training, look for a style with an adjustable band and separate cups instead, and use the same five checks to judge it.
If you are trying the measuring step for the first time, start with a print you love, like the 
"much much better than expected and the fit is excellent."
Barbara W., verified review of the Blue Majolica Sports Bra.
Our note: the Blue Majolica print pairs with matching full-length leggings, so the band and waistband line up in one print. Wear the set for the jump test before your first class.
Is my sports bra too tight or too loose?
A sports bra is too tight when it leaves deep marks, stops you from taking a full breath, or pushes tissue out at the top or sides. It is too loose when the band rides up your back, the fabric wrinkles over the cups, or you bounce during the jump test. Snug is the target: firm enough to hold, easy enough to breathe.
- Band fits, cups wrinkle: in a pull-on bra, try one size down only if the smaller band still passes the two-finger test.
- Cups fit, band digs: go one size up and run the jump test again.
- Straps carve grooves: fix the band first; straps carry what a loose band drops.
Re-check the fit after you wash it
Your fit check is not finished until the bra has been through the wash a few times. Follow the care label, skip fabric softener and let it air-dry flat or on a rack, the same way we recommend in our guide on how to care for leggings, since stretch activewear fabrics share the same care rules. Then put it back on and repeat the band and jump checks.
Wear a sports bra two or three times a week? Owning two lets each one dry fully between workouts. A solid like the If a new bra fails the checks, you have a fix: Free Exchanges. Each order includes one free size exchange within 100 days of delivery, for the same print and style (Final Sale items excluded), as set out in our exchange policy.
Frequently asked questions
Should a sports bra be tight?
A sports bra should be snug, not tight. The band should hold firmly around your ribs with room for about two fingers underneath, you should be able to take a full breath, and the bra should leave no deep marks after a workout.
How do I know if my sports bra is too small?
Your sports bra is too small if the band digs in or makes deep breaths hard, the straps carve grooves into your shoulders, or breast tissue spills over the top or out at the sides under your arms. Go up one size and repeat the jump test.
My band fits but the cups are too big. What can I do?
Wrinkled or gaping fabric over the cups means the cup area is too big for you. In a pull-on sports bra, try one size down only if the smaller band still passes the two-finger test; if it does not, a style with separate cup sizes will fit you better.
What size sports bra should I get if I am between sizes?
Measure your underbust and chest, and if you fall between two sizes on the FIERCEPULSE size chart, order the size up, which is the chart's own advice. From XS to M the sizes sit only 3/4 inch apart at the underbust, so measure twice and use your chest measurement as the tiebreaker.
How often should I re-check my sports bra fit?
Re-check the band and run the jump test after the first few washes, and again whenever the band starts to ride up or the bra moves during a workout. A band that no longer passes the two-finger test has stopped doing its job.
Measured and ready? Run the five checks on your next bra.
Find your print in our sports bras.
Written by the FIERCEPULSE team, who design every print we sell. Contact our support team with any fit question. Published November 2026.
Sources: On, "How a sports bra should fit: A guide for comfort and support". Shock Absorber fitting guide, SportsShoes.com. University of Portsmouth, Research Group in Breast Health. Size chart and product details from the FIERCEPULSE sports bra product pages, read November 6, 2026. Editorial note: every source link was checked on November 6, 2026.
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