How to Measure for a Sports Bra (Low, Medium, High Impact)
Sports bras live or die on three decisions: band size, cup size, and impact level. Get the band right and the bra works; get the band wrong and it rides up no matter how good the brand is.
Sports bras fail more often than regular bras, and almost always for the same reason: the wrong band size. The straps get the blame ("they keep slipping"), the cups get the blame ("they squish me"), but the actual culprit is usually a band that's a size too big and rides up the back during activity.
Here's how to take the two measurements you need, decide your impact level, and choose between compression and encapsulation styles — the two main sports-bra families.
Step-by-Step: Take the Two Measurements
- Get a soft measuring tape. Wear a non-padded everyday bra, a thin sports bra, or no bra. A padded bra adds 0.5–1 inch.
- Measure underbust. Wrap the tape around your ribcage directly under your breasts, parallel to the floor. Snug. On a normal exhale. The number is your band size in inches.
- Measure bust. Wrap the tape around the fullest part of your breasts, parallel to the floor. Don't compress — let the tape rest at the largest point.
- Subtract underbust from bust. The difference is your cup letter:
| Bust − underbust | Cup letter |
|---|---|
| 1" | A |
| 2" | B |
| 3" | C |
| 4" | D |
| 5" | DD or E |
| 6" | DDD or F |
| 7" | G |
| 8" | H |
| 9" | I |
| 10" | J |
Example: 32" underbust, 36" bust = 32D. Use this size as the starting point — sports bra brands may advise sizing down for compression styles or staying true for encapsulation.
Pick Your Impact Level
| Impact | Activities | Bounce control needed | Bra type |
|---|---|---|---|
| Low | Yoga, Pilates, walking, light strength | Minimal | Compression OK; light pad / wireless |
| Medium | Cycling, hiking, dance, moderate strength training, elliptical | Moderate | Compression for A–C; encapsulation for D+ |
| High | Running, HIIT, basketball, kickboxing, jump rope | Maximum | Encapsulation always for D+; combination for A–C |
| Extra-high | Marathon, sprint training, plyometrics | Maximum + secondary support | Encapsulation with hook closure, adjustable straps, often a second compression layer |
Buying a low-impact bra for running means breast pain and motion that strains the Cooper's ligaments (the connective tissue that holds breast shape). Buying a high-impact bra for yoga is just uncomfortable. Match impact to activity.
Compression vs Encapsulation vs Combination
Compression sports bras
Encapsulation sports bras
Combination sports bras
Sports Bra Size Lookup
| Underbust | Bust | Cup | Compression letter (S/M/L) | Encapsulation size |
|---|---|---|---|---|
| 28–30" | 31–33" | B | XS | 30B / 32A |
| 30–32" | 33–35" | B | S | 32B / 34A |
| 32–34" | 35–37" | C | S–M | 34B / 32C |
| 32–34" | 36–38" | D | M | 32D / 34C |
| 34–36" | 37–39" | C–D | M | 36B / 34C |
| 34–36" | 39–41" | D–DD | L | 34DD / 36D |
| 36–38" | 41–43" | DD–DDD | L–XL | 36DDD / 38D |
| 38–40" | 44–46" | DDD–G | XL | 38DD / 40D |
For exact sizing across encapsulation styles, see our bra size chart and the sister size guide if your band is between sizes.
The Two-Finger Test for Fit
After putting on a sports bra, check fit with these tests:
Common Mistakes
Buying a band size up for comfort
"Comfort" by sizing up loosens the band — and the band is what stops bounce. A loose band means a sports bra that doesn't do its primary job no matter how high-impact-rated.
Skipping cup size in compression bras
Compression bras sized only by S/M/L often have an implied cup ceiling. A D+ cup in a compression L will overflow regardless of band fit. Check the brand's chart for cup-to-letter mapping.
Wearing the same sports bra for years
Elastic dies. After 70 washes (or 6–12 months of regular use), a sports bra has lost most of its compression. Replace at the same cadence as running shoes.
Using high-impact bras for everything
High-impact bras are heavy, often unbreathable, and over-engineered for yoga or walking. Use the right impact level for the activity.
FAQs
How do I measure for a sports bra?
Measure underbust (snug, parallel to floor) and bust (relaxed). Underbust is band size; bust minus underbust is cup difference.
What's the difference between compression and encapsulation?
Compression flattens tissue against the chest (good for A–C, low/medium impact). Encapsulation has separate cups (required for D+ or high impact).
What size sports bra do I need for running?
High impact, encapsulation if D+. Often size down one band from your everyday band size; brands stretch with use.
Should sports bras fit tighter than regular bras?
Yes. Most support comes from the band, so it should be snugger than an everyday bra.
How often should I replace a sports bra?
Every 6–12 months for active wear, or 70 washes.
Can I wear my regular bra size in a sports bra?
Sometimes. Compression bras often use S/M/L; encapsulation uses traditional band-cup. Check the brand's specific chart.
Three Decisions: Band, Cup, Impact
That's all sports bra sizing comes down to. Take the two measurements once, decide your impact level by activity, and pick compression or encapsulation by cup size. The rest is brand-specific fine-tuning.
For full bra sizing reference see our bra size chart and what is a sister size bra for cup-volume swaps when bands run between sizes.
Selling activewear on Shopify? Sports bras are the highest-return category.
Tailor Size Guide adds underbust + bust matching to every sports bra so customers find their right band-and-cup the first time.