A well fitted bra can change your entire day, from how your clothes look to how your body feels. The problem? Most women are wearing the wrong bra size, and many don’t even know it. The good news is that learning how to measure bra size with measuring tape is easy and takes just a few minutes at home. No professional fitting required, no fancy tools needed—just a soft measuring tape and a mirror.
What You’ll Need Before Measuring
Before you start measuring, make sure you’re wearing a thin, non-padded bra. This gives your breasts shape without adding volume, which helps get a more accurate bust measurement. Stand in front of a full-length mirror if possible. This will help you make sure your tape measure stays straight and level across your back.
Grab a soft fabric measuring tape (the kind used in sewing), a pen or your phone to note your numbers, and take a deep breath. Relax. Posture matters when you’re measuring—stand up tall but keep your shoulders relaxed.
Step 1: Measure Your Band Size (Underbust Measurement)
Start by wrapping the measuring tape directly under your bust, where your bra band usually sits. This should be just beneath the breast tissue, resting firmly against your ribcage. Check in the mirror that the tape is completely level—not tilted up in the back.
Make sure the tape is snug but not too tight. You should be able to slide one finger under it, but no more.
-
If your measurement is an even number, that’s your band size.
-
If it’s an odd number, round up to the next even number. So, if you measure 33 inches, your band size is 34.
Band size is one of the most overlooked parts of bra fitting, but it’s essential. It’s where most of the bra’s support comes from—not the straps!
Step 2: Measure Your Bust Size (Overbust Measurement)
Now wrap the tape measure around the fullest part of your bust. This is usually across your nipples. Again, check the mirror to make sure the tape is lying flat and straight, not riding up or drooping.
Hold the tape comfortably—not too tight, but not loose either. You want a close fit that doesn’t flatten your breasts.
Take this number and jot it down. This is your bust measurement.
Step 3: Calculate Your Cup Size
Now comes the fun part: figuring out your cup size. It’s a simple math equation:
Bust Measurement - Band Measurement = Cup Size Number
Each inch of difference between your bust and band size equals one cup size. Here’s a quick reference:
-
1 inch = A cup
-
2 inches = B cup
-
3 inches = C cup
-
4 inches = D cup
-
5 inches = DD or E
-
6 inches = DDD or F
-
7 inches = G, and so on
Let’s say you measure 34 inches under your bust and 37 inches at the fullest part. That’s a 3-inch difference, which means you’re a 34C.
Simple, right?
Check the Fit (Don’t Just Trust the Math)
Even if your numbers tell you you’re a 34C, the real test is how that bra feels. Numbers get you close, but every body is different. Breast shape, spacing, and firmness all play a role. So once you’ve figured out your size, try on bras in that size—and a sister size or two just in case.
Here’s how a properly fitted bra should feel:
-
The band should feel snug, staying in place even if you lift your arms.
-
The straps should not dig in or fall down. They’re just there to give a little lift.
-
The cups should contain your breasts fully without gaping or spilling over.
-
The center of the bra (the gore) should lie flat against your chest.
If one or more of these things feel off, it’s time to try a different size—or style.
What Are Sister Sizes and Why They Matter
Sister sizes are alternate bra sizes that have the same cup volume but different band sizes. For example, if you’re a 34C, your sister sizes are:
-
32D (tighter band, larger cup)
-
36B (looser band, smaller cup)
This matters because bra sizing isn’t standardized between brands. You might be a 34C in one store and a 32D in another. Trying on your sister sizes can help you find the perfect fit, especially if your measurements fall between two sizes.
Measure Again Every Few Months
Your bra size can change more often than you think. Weight changes, aging, pregnancy, breastfeeding, and even certain medications can impact your bust and band size. That’s why it’s smart to remeasure yourself every 6 to 12 months or anytime your bra starts feeling uncomfortable.
If you notice your straps falling, band riding up, or constant adjusting, don’t ignore those signs—your size may have shifted.
Signs You’re Wearing the Wrong Bra Size
If you’re constantly feeling uncomfortable in your bras, chances are the fit is off. Here are some common red flags:
-
Cup spillage or gaping
-
Underwire poking or floating
-
Straps digging into your shoulders
-
Back band riding up
-
You feel sore or tired at the end of the day
A properly fitted bra should make you feel supported, not suffocated. You shouldn’t want to rip it off the second you walk in the door.
Different Styles, Different Fits
Not all bras are built the same. A plunge bra fits differently than a full-coverage bra. A bralette has less structure than an underwire. Once you know your measurements, explore different styles. You might find you need a slightly different size in a strapless bra compared to your everyday t-shirt bra.
Don’t be afraid to try new shapes. Sometimes the best-fitting bra isn’t the one you’re used to—it’s the one you haven’t discovered yet.
Final Thoughts
Measuring your bra size with a measuring tape is one of the easiest ways to feel better in your clothes, boost your posture, and avoid daily discomfort. With just two simple measurements, you’ll have the numbers you need to start shopping smart. Remember: your bra should work for you—not against you.
If your current bras are uncomfortable, sagging, or just feel wrong, don’t ignore it. Take five minutes, grab a measuring tape, and take control of your fit..
FAQs
Can I measure my bra size without a measuring tape?
You can try using string and a ruler, but a soft measuring tape gives more accurate results.
Should I measure over or under clothes?
Measure over a thin, unpadded bra—or bare if needed. Avoid bulky clothing.
What’s the best time of day to measure?
Midday is best. Measuring in the morning or after a workout can give inaccurate results due to body fluid shifts.
