Bra Size Calculator

Getting the right bra size starts with two simple measurements: your underbust (band) and your bust at the fullest point. Enter those numbers into the calculator above, and you'll get your estimated band size, cup size, and sister sizes in seconds.

Most people wear the wrong bra size. Studies suggest up to 80% of women do. A properly fitted bra improves comfort and support throughout the day. This calculator helps you find your starting point so you can shop with confidence.

Measure Your Bra Size With the Bra Size Calculator

The bra size calculator needs just two inputs: your band measurement and your bust measurement. Both are taken with a soft measuring tape wrapped snugly around your torso.

Here's the quick version:

1. Measure around your ribcage, just under your bust, for the band size.
2. Measure around the fullest part of your bust for the bust size.
3. Enter both numbers into the calculator.

The tool does the math for you. It rounds your band measurement to the nearest whole number, calculates the difference between bust and band, and maps that difference to a cup letter.

This is an estimate. Bra sizes vary between brands, so treat the result as your best starting point rather than a guaranteed fit.

How to Use a Measuring Tape for Measuring Bra Sizes Accurately

Accurate measurements matter. Even a half-inch difference can shift your cup size. A soft measuring tape is the best tool for the job.

Stand in front of a mirror if possible. Wear an unlined or lightly lined bra (no padding) or go without. Keep the tape parallel to the floor for both measurements.

No soft measuring tape on hand? Use a piece of string. Wrap it around your body, mark where the ends meet, then lay the string flat against a ruler or hard tape measure. It works well in a pinch.

Underbust and Band Size

Wrap the measuring tape around your ribcage, directly under your bust. The tape should feel snug but not tight. You should be able to slide two fingers under the band comfortably.

Exhale normally before reading the number. Don't suck in or puff out.

• If the number is even (e.g., 32, 34, 36), that's your band size.
• If the number is odd, round to the nearest even number.

The band provides most of the support in a bra. Getting this measurement right is the single most important step.

Bust Size and the Fullest Part

Wrap the measuring tape around the fullest part of your bust. Keep the tape parallel to the floor and avoid pulling it tight. It should rest gently against your skin.

The fullest part of your bust is usually at nipple level, but not always. Lean forward slightly and let gravity help you find the spot where you measure the largest circumference.

Write down this number. The calculator uses the difference between your bust measurement and your band measurement to determine your cup size.

How Bra Cup Size and Cup Sizes Are Calculated

Cup size is not a fixed volume on its own. It represents the difference between your bust measurement and your band size.

Here's how the math works:

Each inch of difference equals one cup size. So if your band measures 34 inches and your bust measures 37 inches, the difference is 3 inches, giving you a 34C.

What is ABCD in bra sizes? These letters simply label the cup depth. A is the smallest standard cup. B adds one more inch of cup volume, C adds another, and so on. Beyond DD, sizing conventions differ by brand and region.

What is the smallest bra size? In standard US sizing, that's typically 28AA or 30AA. Availability depends on the brand.

Bra Size Chart for All Bra Sizes

A bra size chart gives you a quick visual reference. Below is a simplified US sizing chart showing common band and cup size combinations.

The number in each bra size is the band. The letter is the cup. Together, band and cup size define the overall fit.

Remember, bra sizes vary between brands. A 34C in one brand may feel like a 34B or 34D in another. Use this chart as a reference, not a guarantee.

Sister Size and Bra Cups

Sister sizes are bra sizes that share the same cup volume but have different band sizes. They're useful when your usual size isn't available or when a brand runs slightly large or small.

The rule is simple:

• Go up one band size, go down one cup size.
• Go down one band size, go up one cup size.

For example, these three sizes all share the same cup volume:

• 32D
• 34C
• 36B

Is 34B or 32C bigger? They hold the same cup volume. The difference is the band. A 32C has a tighter, smaller band. A 34B has a looser, larger band. Neither is "bigger" overall.

Sister sizes are a useful trick, but they have limits. Moving more than one band size in either direction usually changes the fit too much for comfort and support.

Does the cup change when I change band size? Yes, always. Cup size is relative to band size. A D cup on a 32 band is a smaller volume than a D cup on a 38 band.

Using the Bra Size Calculator to Find Your Bra Size

Here's a step-by-step walkthrough of the calculator:

1. Take your measurements. Measure your underbust and bust as described above.
2. Enter the numbers. Type your band measurement and bust measurement into the calculator fields.
3. Read your results. The calculator returns your estimated bra size (band + cup) and your closest sister sizes.

That's it. The whole process takes under a minute.

Should I measure with or without a bra on? Ideally without a bra, or in a thin, unpadded bra. Padded bras add volume to your bust measurement and can skew results.

How often should bra size be measured? At least once a year. Weight changes, hormonal shifts, pregnancy, and aging can all affect your bra size. If your current bra size feels off, re-measure before buying new bras.

Bra Fit: Signs You Have the Correct Bra

A calculator gives you a starting size. Fit confirms it. Here's what to check once you put a bra on.

A properly fitted bra should feel comfortable from the moment you clasp it. You shouldn't need to "break it in." If something digs, gaps, or rides up, the size or style likely isn't right.

Band, Strap, and Underwire Bra Fit

Band: The band should feel snug on the loosest hook. You should be able to slide two fingers under the band across your back, but it shouldn't ride up. If the band rides up at the back, it's too loose. Go down a band size.

Straps: Straps should stay on your shoulders without digging in. If they dig into your shoulders, the band may be too loose (forcing the straps to carry too much weight). The band, not the straps, provides most of the support.

Why do my bra straps keep falling off? The straps may be set too wide for your shoulders, or the band may be too large. Try tightening the straps first. If that doesn't help, try a smaller band with the next cup size up.

Underwire: The underwire should lie flat against your ribcage and fully enclose your breast tissue. If the wire sits on breast tissue, try a larger cup. If it pokes out too far past your breasts, try a smaller cup.

Why does my bra leave marks? Light marks from the band or straps at the end of the day are normal. Deep red marks, pain, or indentations that last more than a few minutes suggest the fit is too tight in that area.

Breast Shape and Volume

Cup fit isn't only about size. Breast shape affects which bra styles work best.

• Full on top: A full-coverage or balconette style often works well.
• Full on bottom: Plunge or demi styles tend to fit better.
• Wide-set: Look for bras with a wider center gore.
• Close-set: Plunge styles with a narrow center gore may feel more comfortable.

If you notice spillage over the top of the cups, try going up a cup size. If the cups wrinkle or gap, try going down. The cups should lie smooth against your skin with no overflow and no empty space.

The volume of your breasts also matters when choosing between padded, unlined, or lightly lined styles. Padding adds shape and coverage but also changes how a size feels. An unlined bra gives you a truer sense of whether the cup size is accurate.

Size Accurately: When to Get a Fitting

A calculator is a great starting point. A professional fitting takes it further.

Consider getting fitted in these situations:

• Your bra never feels right, no matter what size you try.
• You've recently experienced a significant weight change.
• You're pregnant, nursing, or postpartum.
• You're buying a specialty style like a strapless or sports bra for the first time.
• You find yourself between cup sizes.

Many lingerie shops and department stores offer free fittings. A trained fitter can assess band fit, cup volume, breast shape, and strap placement in a way no online calculator can replicate.

What are the impacts of wearing the wrong bra size? Beyond discomfort, a poorly fitting bra can cause shoulder pain, back pain, skin irritation, and poor posture. A band that's too loose won't support properly. Cups that are too small can compress breast tissue uncomfortably.

How often should I replace my bra? Most bras last about 6 to 12 months with regular wear. When the band stretches out (even on the tightest hook), when the cups lose shape, or when the underwire pokes through, it's time for a replacement.

Find Your Perfect Fit With the Right Bra

Start by entering your measurements into the bra size calculator above. Use the result as your baseline, then fine-tune with the fit checks outlined on this page.

The right bra should provide comfort and support without constant adjusting. Finding it sometimes takes trying a few sizes, styles, or brands. That's normal.

Keep these takeaways in mind:

• Measure your underbust and bust with a soft measuring tape, keeping the tape parallel to the floor.
• Use the calculator to get your estimated band and cup size.
• Check sister sizes if your calculated size isn't available.
• Always test band, strap, and cup fit before committing.
• Re-measure at least once a year, or after any body changes.

Your perfect bra size is the one that fits well, feels comfortable, and supports you through the day. The calculator gets you close. Trying it on gets you there.