Still lost in a sea of letters and numbers? You're definitely not alone. Data shows that every month, tens of thousands of women search for "measurements for cup sizes" and "bra cup sizes," yet finding the perfect fit remains a challenge. The truth is, your size is more than just a single letter. Whether you're wondering, "What cup size is 5 inches?" or asking yourself, "Is a 36C the same as a 34D?" (spoiler: they're sister sizes!), this guide has the answers.  At Yvette Sports, we believe a well-fitting sports bra is the foundation of every great workout. Follow our foolproof measurement guide to find your "Magic Number" in minutes.

 

 

 

How do I Figure out What My Cup Size is?

Step 1: Prep & Precision — Setting the Stage for the Perfect Fit

Before you grab the tape, let's get the basics right. Accuracy starts with the right environment.

The Gear 

You'll need a flexible fabric measuring tape (don't use a metal construction tape!) and a full-length mirror.

The Outfit

Wear your best-fitting, non-padded underwire bra. Avoid sports bras or push-ups, as they compress or shift your natural shape.

The Stance

Stand tall and relaxed in front of the mirror to ensure your tape stays level.

 

 

 

1. Find Your Band Size (The Foundation)

The band provides 80% of your bra's support, so getting this number right is crucial.

 • The Action: Wrap the measuring tape snugly around your ribcage, directly underneath your bust (the under bust area).

 • Pro Tip: Keep the tape parallel to the ground. It should feel "snug but not tight"—you should be able to slide exactly one finger comfortably under the tape. 

• The Reading: Take a deep breath in, exhale fully, and note the measurement in inches.

• The Calculation (The +4/+5 Rule): If your measurement is an even number, add 4 inches.

• If your measurement is an odd number, add 5 inches.

• Example: If you measure 30", your Band Size is 34. If you measure 31", your Band Size is 36.

 

2.  Find Your Bust Size (The Volume)

This measurement helps determine your cup volume relative to your band.

 • The Action: For the most accurate reading, lean forward slightly at the hips so your chest drops into the tape. Wrap the tape around the fullest part of your bust (typically across the nipple line).

 • The Fit: Ensure the tape is level across your back. Do not pull it tight; it should just rest gently against your skin without indenting the tissue.

• The Reading: Stand naturally and record the measurement in inches. No need to hold your breath here—just keep it steady.

 

 

Why Accuracy Matters - Bra Size Calculator in Inches

Most women wear a band that is too large and cups that are too small. By following these precise steps, you're moving away from "guessing" and toward a performance-ready fit that prevents bounce and eliminates shoulder strain.

 

 

 

How do I Calculate my Cup Size?

 

Step 2:  The Final Math — Cracking the "Cup Size" Code

 Now that you have your measurements, it’s time to answer the million-dollar question:

"How do I calculate my cup size?" Many people think cup size is an absolute volume, but in the world of professional bra fitting, it’s actually a relative measurement.

 Your cup size is determined by the difference between your Bust Size and your Band Size.

 The Golden Formula: Bust Size – Band Size = Your Cup Size (The Difference in Inches)

 The Universal Sports Bra Size Chart 

 

Use the difference you calculated to find your corresponding letter in the table below. This is the industry standard used by Yvette Sports and most major athletic brands.

Let’s Put It into Practice: An Example 

If you’re still unsure, let’s walk through a quick calculation together.  

Your Measured Bust Size: 39 inches 

Your Calculated Band Size: 36 inches

 

 

The Result: A 3-inch difference translates to a C Cup. Combining this with your band measurement, your perfect fit is a 36C.

 

Even with a perfect measurement, "bra math" can be tricky. Here are the most common questions we get from our community to help you fine-tune your fit.

 

 

 

Is a 36C the same as a 34D?

 

This is perhaps the most famous question in the world of lingerie! The short answer is: In terms of cup volume, yes. This concept is known as "Sister Sizes." While a 34D and a 36C hold roughly the same amount of breast tissue, the difference lies in the band proportions.

 

Choose a 34D if you have a smaller frame but more projection/fullness. It offers a tighter, more supportive band.

 

Choose a 36C if you prefer a slightly more relaxed feel around your ribs.

The Takeaway: If you find a 36C is "almost" right but the band feels loose and rides up your back, try your sister size: 34D. For reference, other common sister sizes include 32D/34C/36B.

 

 

 

 

 

 

How do I Know if My Cup is B or C ?

 

This is the ultimate "in-between" struggle. As we discussed in Step 2, the difference is all in the math:

B Cup: A 2-inch difference between your bust and band.

C Cup: A 3-inch difference.

 

What if you’re exactly 2.5 inches? Since every body is unique and bra materials vary, you should look for these physical "fit cues" to decide:

 

Signs you need a C Cup: If you’re wearing a B cup and notice "quad-boobing" (tissue spilling over the top), or if the center gore (the fabric between the cups) doesn't lay flat against your chest, you need to size up.

 

Signs you need a B Cup: If there is any "gaping" or wrinkling in the fabric of a C cup, or if the cups feel hollow at the top, the B cup will provide a more secure, "locked-in" feel—especially important for high-impact sports.

 

 

 

 

 

 

How do You Find Your Cup Size on a Bra ？

 

Even with the math done, the "mirror test" is the final word. Before you hit "add to cart," run through this quick checklist to ensure your new Yvette Sports bra is a high-performance fit, not just a guess.

 

1. The Level Check: Is Your Tape (and Band) Straight?

Accuracy starts with a horizontal line. When measuring, and later when wearing your bra, check your side profile in the mirror. 

The Pitfall: If the tape or the bra band is sliding up your back, your measurement will be skewed (usually resulting in a band that’s too large).

The Fix: Ensure the band sits in a perfectly straight, horizontal line from front to back. If it arches up in the back, you likely need a smaller band size.

 

2. The Band Tension: The "Two-Finger" Rule

The band is the engine of your bra—it provides the vast majority of your support.

The Pitfall:  buying a bra that only feels tight on the tightest hook.

 The Fix: A brand-new bra should fit snugly on the outermost (loosest) hook. This allows you to tighten the bra as the elastic naturally stretches over time. You should be able to slide two fingers under the band comfortably, but no more. If it’s looser than that, your "Magic Number" might be a size down.

 

3. The Cup Silhouette: No Gaps, No Spills

Your breast tissue should be fully contained within the cups for maximum stability during movement.

The Pitfall: "Gaping" (empty space at the top of the cup) or "Spilling" (the dreaded "quad-boob" or side-bra bulge).

The Fix: The fabric should lay flat against your skin. If you’re wearing an underwire style, the wire should sit comfortably behind your breast tissue, not on top of it. If you see wrinkling, try a cup size down; if you see "overflow," try a cup size up.

 

4. The Strap Test: The 80/20 Rule

Many people over-tighten their straps to make up for a loose band, which leads to painful shoulder "digging."

The Pitfall: Straps that leave red marks or feel like they’re doing all the heavy lifting.

The Fix: Remember the 80/20 rule: 80% of your support comes from the band, and only 20% from the straps. Your straps should be adjusted to stay in place and provide a gentle lift, but they shouldn't be carrying the full weight of your bust.

 

 

How can You Tell What Bra Size You are ?

 

At the end of the day, finding your "Magic Number" isn't just about clearing up confusion—it’s about your long-term well-being and confidence. Whether you’re shopping for a sleek, everyday B cup bra or hunting for the ultimate high-impact DD bra size, the right fit is the foundation of your wardrobe and your health.

 

1. Aesthetics Meet Confidence

A well-fitting bra does more than just "hold things in place." It lifts your silhouette, improves your posture, and makes your clothes hang exactly the way they were designed to. When you stop worrying about straps slipping or bands digging, your confidence shines through.

 

2. The Science of Support: Protecting Your "Cooper’s Ligaments"

This is the part many brands overlook: your breasts are supported by thin, fibrous tissues called Cooper’s ligaments.

The Risk: Once these ligaments stretch due to repetitive bouncing or poor support, they cannot "bounce back." This is a leading cause of premature sagging.

The Solution: A professionally fitted sports bra acts as a structural shield, minimizing vertical and lateral movement to keep these tissues intact.

 

3. Say Goodbye to Exercise-Induced Breast Pain

If you’ve ever cut a workout short because of discomfort, you’re not alone. Research shows that a significant percentage of women experience breast pain during exercise due to inadequate support.

By wearing the correct size, you reduce breast displacement by up to 80%.

This doesn't just eliminate pain; it improves your running economy and athletic performance. When you aren't fighting discomfort, you can focus on hitting that next Personal Best (PB).

 

 

 

 

We understand that everybody is unique. We are committed to providing every woman with a "tailor-made" comfort experience. Don't forget to check out our sports bra size guide to find the perfect one for you.