Your Bra Cup Sizes Guide

Your bra cup size represents breast volume relative to your band size, it’s not simply a standalone letter that means “big” or “small.” A 34C and 38C do not share the same cup volume; the cup letter always depends on the band number it’s paired with.

Cup size is calculated from the difference between your bust measurement (around the fullest part of your breasts) and your underbust measurement (snugly around your ribcage). Each inch of difference corresponds to a cup letter in US and UK sizing systems.

Here’s a quick example to illustrate:

• Underbust measurement: 32 inches

• Bust measurement: 36 inches

• Difference: 4 inches

• Result: 32D in US sizing

This cup sizes guide focuses on practical understanding for everyday shopping in 2026. Whether you’re buying online from different countries, switching brands, or noticing your old bras no longer fit, these fundamentals will help you navigate the often confusing world of bra sizing with confidence.

What Does Cup Size Actually Mean?

Cup size functions as a “volume category” derived from the difference between your bust and band measurements. It’s not an absolute measurement, it’s always relative to the band it accompanies. For more on maintaining optimal support and learning when it's time to replace your bras, see our guide on bra failure.

The standard inch-based method used in US and UK sizing works like this:

• 1-inch difference = A cup

• 2-inch difference = B cup

• 3-inch difference = C cup

• 4-inch difference = D cup

• 5-inch difference = DD or E cup

• 6-inch difference = DDD or F cup

• 7-inch difference = G cup

To visualize how cup volume increases on a 32 band:

• 32A: Bust measures 33 inches (1-inch difference)

• 32B: Bust measures 34 inches (2-inch difference)

• 32C: Bust measures 35 inches (3-inch difference)

• 32D: Bust measures 36 inches (4-inch difference)

• 32DD: Bust measures 37 inches (5-inch difference)

• 32F: Bust measures 38 inches (6-inch difference)

• 32G: Bust measures 39 inches (7-inch difference)

Double letters like DD and FF in UK sizing are intermediate steps in the progression, they’re not “twice as big” as their single-letter counterparts. Some brands use E instead of DD, and F instead of DDD, depending on whether they follow US or UK conventions. This is why checking a brand’s specific sizing chart before purchasing is essential.

How to Measure for Accurate Cup Size (Step-by-Step, 2026 Method)

Accurate measuring at home in 2026 is far more reliable than outdated “+4 inches” rules from mid century sizing conventions. Modern brands, especially those specializing in fuller busts, now recommend the “+0” method for a truer fit. The cup size increases by one letter for every inch of difference between the bust and under-bust measurements, starting from A. The visual differences between cup sizes can be significant, with real life photos showing the variations in volume and projection.

What you’ll need:

• Soft tape measure marked in inches or cm

• A mirror

• A non-padded or lightly lined bra (or measure braless)

Step 1: Measure Your Band/Underbust

• Wrap the tape measure snugly under your bust at the inframammary fold (where your breast tissue meets your chest wall)

• Keep the tape parallel to the floor

• Exhale normally before reading the measurement

• The tape should be tight enough that you can only slip one finger underneath

Step 2: Measure Your Bust/Overbust

• Wrap the tape around the fullest part of your breasts

• Keep the tape level at the back with your arms relaxed at your sides

• The tape should be loose enough to avoid compressing breast tissue

• For fuller cups (D+), repeat this measurement while leaning forward at 90 degrees, this captures projected tissue more accurately

Step 3: Round Your Measurements

• In inches: round to the nearest whole number

• In cm: round to the nearest 0.5 or 1 cm depending on local standards

• For underbust, round to the nearest even number for your band size

Step 4: Calculate Your Cup Size

• Convert underbust to band size (e.g., 31 inches → 32 band)

• Subtract band from bust measurement

• Match the difference to the corresponding cup letter

Worked Example:

• Underbust: 29.5 inches → rounds to 30 band

• Bust: 35.5 inches → rounds to 36 inches

• Difference: 36 - 30 = 6 inches

• Result: 30DDD/F

For women with very soft or heavy breasts, taking both a standing straight measurement and a lying flat measurement, then averaging them, can provide a more realistic cup estimate.

Cup Size Progression & Volume: From AA to H in 2026

Cup volume increases stepwise, but the perceived change feels almost exponential by the time you reach DD through H cup sizes. Each step adds roughly the same volume increment for a fixed band, but the visual and structural impact compounds.

Sister sizes change the band size while keeping the cup volume constant (e.g., 34C to 36B). Common initial cup sizes include AAA, AA, A, B, C, D, DD+, with variations in US and UK sizing for larger sizes. Half sizes are available from some brands to accommodate for gaps or overflow in standard cup sizes. The bust size is measured around the fullest part of the breasts while standing straight with arms to the side. For accurate measurements, it is recommended to measure braless and to use a soft tape measure. It is important to retake measurements periodically as body size can change due to various factors such as weight fluctuations and hormonal changes.

Bra sizing systems vary significantly between countries and brands, leading to confusion for consumers. The U.S. uses a system where cup sizes increase by 1 inch, while many European systems increase cup sizes by 2 centimeters. In the UK, bra sizes range from A to LL, while in the U.S., sizes typically go from A to G, with some brands offering larger sizes. The French and Spanish bra sizing systems are based on the Continental European sizing system, with band sizes being 15 cm larger than the European sizes. In Australia and New Zealand, cup sizes generally follow the UK system for smaller sizes but switch to European labels for larger sizes.

The typical progression in US/UK systems runs:

• AA → A → B → C → D → DD/E → DDD/F → G → H

On a 32-band frame, moving from A to H represents roughly a 10-12x increase in total breast volume. Here are approximate per-breast volume ranges commonly cited in 2026 industry standards:

• 32A: approximately 150-200 cc

• 32C: approximately 350-450 cc

• 32DD: approximately 600-750 cc

• 32G: approximately 1100-1300 cc

• 32H: approximately 1500-1800 cc

The volume of a 32A cup is approximately 200cc, while a 32DD cup is around 700cc, and a 32G cup is about 1200cc. Keep in mind that actual bodies vary significantly, these figures provide general guidance rather than exact specifications.

The same cup letter on a larger band spreads volume over a wider chest. A 38D distributes its cup volume across a broader torso, appearing less projected than a 32D despite sharing the letter. This is why band and cup sizes must always be considered together.

For larger cup sizes (G cup, H, and above), specialized bra designs become essential. These typically feature:

• Wider underwire spans

• Stronger side wings for stability

• More structured, multi-part cups

• Reinforced fabric with minimal stretch in load-bearing areas

Proper support for larger sizes (D and above) often requires wider bands and reinforced structures. Some signs of incorrectly fitted bras include the band digging into the torso or sliding upwards, red marks, shoulder or neck pain, and the breasts overflowing around the edges of the bra. If the band rides up the torso at the back, the band size is too big. A good fitting bra is comfortable and you don't feel like you're wearing one. If you feel like your bust isn't properly supported then it's because it isn't: the cups are loose or the top of the cup doesn't touch your skin. If the band digs into the flesh, causing the flesh to spill over the edges of the band, the band is too small.

Visualizing Cup Sizes: Letter by Letter Examples

Letters alone can be misleading without context. A “D cup” means completely different things on a 30 band versus a 40 band. The following examples all use a 32 band so you can compare relative volume at the same frame size.

• 32A: Minimal volume with low projection. Often comfortable in bralettes, wireless designs, or lightly lined T-shirt bras. Many women in this range prioritize comfort over structure.

• 32C: Moderate everyday volume that remains common among women in their 20s and 30s. Well-suited to classic T-shirt bras, balconette styles, and most mainstream designs without requiring specialized construction.

• 32DD/E: Fuller bust with noticeable projection. Requires a firm band and well-shaped underwire for proper comfort and support. Side support panels become helpful at this size.

• 32G: Significant volume and projection that usually needs bras engineered specifically for fuller busts. Look for wide straps, side support construction, and multi-part cups that shape and distribute weight effectively.

• 32H: Very high volume demanding wide bands, strong side wings, and typically balconette or full-cup patterns to distribute weight properly. Fabric quality and construction become critical factors.

These differences affect how clothing fits. Women wearing DD+ cup sizes often experience button up shirts gaping at the bust, necklines that reveal more than intended, and the need to size up tops to accommodate chest measurements while the rest of the garment fits loose.

International Cup Sizes & Conversions (US, UK, EU, FR/ES, AU/NZ)

Cup letters don’t map 1:1 across different countries, especially once you move above a D cup. Understanding these differences prevents expensive mistakes when shopping internationally.

The main systems:

• US/UK: Inch-based with double letters (DD, FF, GG) for intermediate sizes

• EU: Centimeter-based with single letters (A through K), where cups increase every 2 cm rather than every inch

• FR/ES: Add 15 cm to EU band sizing (EU 70 = FR 85)

• AU/NZ: Use dress-size-based band labels (10, 12, 14 instead of 32, 34, 36)

At smaller sizes (A through C), cup letters usually match across systems. From D upward, names diverge significantly.

Concrete conversion examples:

• 34DD (US) ≈ 34E (UK) ≈ 75E (EU)

• FR 90C = EU 75C = UK 34C

• AU 12D ≈ UK 34D

• US DDD = UK F (same volume, different naming)

A European size will use a completely different band number a UK 32D translates to EU 70D, where 70 represents centimeters rather than inches.

Always check a detailed conversion chart or the specific retailer’s size guide when buying internationally, especially for D+ cups. Some 2026 brands have simplified labeling by dropping double letters entirely, jumping straight from D to E to F, which affects how traditional DD and DDD sizes translate.

Understanding Sister Sizes: Same Cup Volume, Different Bands

Sister sizes are different band and cup combinations that share the same cup volume. They’re a powerful tool for fine-tuning fit when your measurements fall between standard sizes.

The principle works like this: going down one band size and up one cup letter keeps the cup volume similar while tightening the band. Going up one band size and down one cup letter loosens the band while maintaining volume.

Sister size chain example (medium volume):

30D = 32C = 34B = 36A

All four combinations contain approximately the same cup volume distributed across progressively wider torso frames.

Sister size chain example (fuller volume):

32G = 34FF = 36F = 38E

Again, these share similar cup volume despite different band and cup labels.

How to use sister sizes in practice:

• If your calculated size feels too tight in the band but the cups fit well, try one size up in band and one size down in cup

• If you want more support but the cups are right, try one size down in band and one size up in cup

• Use sister sizes when a brand doesn’t carry your exact size

However, sister sizes are a fine tuning tool, not a substitute for finding your fundamentally correct base size. If you’re off by more than one sister size in either direction, the fit will likely suffer regardless.

Fit Check: Is Your Cup Size Right?

Research between 2010 and 2024 consistently shows that 70-85% of women wear the wrong cup and band size combination. A properly fitted bra should feel comfortable, provide support without restriction, and work invisibly under clothing.

Signs your cup is too small:

• Breast tissue spilling over the top or sides of the cup

• The bra’s center panel (gore) floating away from your breastbone instead of lying flat

• Underwire sitting on breast tissue rather than in the inframammary fold

• “Quad-boob” effect creating visible lines under fitted clothing

• Red marks on breast tissue from underwire pressure

Signs your cup is too big:

• Wrinkling or gaping at the top of the cup

• Cup edge not lying flat against the breast

• Needing to tighten straps excessively to make the cup appear full

• The bra cup puckering when you move

Cup problems often relate to band problems. A band that’s too loose allows the bra to ride up in back, pushing cups forward and mimicking a too-small cup. Conversely, a too-tight band can force breast tissue out of cups that would otherwise fit.

At-home fit test:

1. Put on your bra and do the “scoop and swoop”, lean forward, settle each breast fully into its cup, then straighten up

2. Check that the center gore lies flat against your breastbone

3. Verify the underwire follows your breast root without sitting on tissue

4. Ensure the band sits level and parallel to the floor

5. Confirm straps provide support without digging into your shoulder

Breast asymmetry affects 20-25% of women by up to one cup difference between sides. The standard advice: fit the larger breast and use removable padding or inserts to balance the smaller side.

Cup Sizes by Body Changes: Pregnancy, Weight & Hormones

Cup size is not a fixed measurement. Most women experience several significant changes between ages 18 and 50+, making periodic re-measurement essential.

Menstrual cycle fluctuations:

• Some women experience monthly volume swings up to 20%, especially in D+ cups

• Breast tenderness and temporary swelling are common in the week before menstruation

• Stretch lace cups and flexible fabrics accommodate these changes better than rigid molded cups

Pregnancy and breastfeeding:

• Many women go up 1-3 cup sizes between first trimester and postpartum

• Band sizes often increase 1-2 sizes as the ribcage expands

• Breast volume can fluctuate significantly during nursing, often within the same day

• Post-weaning, some women return to pre-pregnancy size while others remain larger or smaller

Weight changes:

• Gaining or losing 5-10 kg typically alters both band and cup size

• Breasts contain fatty tissue that responds to overall body composition changes

• The ratio of change varies individually, some women lose or gain primarily in the bust, others see minimal chest changes

Hormonal factors:

• Hormonal contraceptives can increase cup size by 1-2 sizes over several months

• Hormone replacement therapy affects breast tissue density and volume

• Gender-affirming hormone therapy can significantly change breast volume over 6-24 months

Rather than relying on your “favorite size” from years ago, remeasure every 6-12 months or after any significant life change. A bra size calculator can help track these shifts over time.

Cup Size, Styles & Support: Matching Shape to Letter

Cup letter alone doesn’t dictate which bra style works best for you. Breast shape, tissue firmness, and personal comfort preferences all influence ideal style choices.

Common breast shapes and their fit implications:

• Full on top: Volume concentrated above the nipple; works well with balconette and plunge styles

• Full on bottom: Volume concentrated below; benefits from full-cup and side-support designs

• Projected: Extends significantly from chest wall; needs cups with depth rather than shallow molded foam

• Shallow: Spreads across chest with less projection; suits demi-cups and bralettes

• Wide set: Significant gap between breasts; benefits from plunge styles with narrow center gores

Style guidance by cup range:

• A-B cups: Bralettes, plunge styles, wireless bras, light lining. Structure is optional, comfort often takes priority.

• C-DD cups: T-shirt bras, balconette styles, lightly padded options, everyday underwire. The sweet spot where most mainstream designs work well.

• F-H+ cups: Full cup designs, side support construction, longline bras for additional stability, structured sports bras with encapsulation. Prioritize wide bands, cushioned wide straps, multi-part cup construction, and fabrics with minimal stretch in the lower cup.

Push up bras visually increase apparent cup size by 1-3 cups through padding and angled construction. This can distort your perception of your “true” size if you’re accustomed to wearing heavily padded styles. When measuring, use a non-padded bra for accurate results.

For the perfect bra fit in larger sizes, look for designs that distribute weight across the band rather than relying on straps. If straps are digging into your shoulder or causing neck pain, the band likely isn’t doing its job, consider sizing down in band and up in cup.

2026 Cup Size Myths vs Facts

Many myths persist online and across social media about what cup letters “really mean.” Here’s what the evidence actually shows.

Myth 1: “D cup is huge.”

Fact: On a 28 or 30 band, a D cup is relatively modest in absolute volume. Average cup sizes in the US and UK have shifted toward D-DD since around 2010, driven by improved fitting awareness and changes in average body composition. A D cup is the most common mistake women make, assuming they’re a C cup when measurement shows D or larger.

Myth 2: “Same letter means same size.”

Fact: A 32D and 38D represent completely different volumes. The same person could theoretically wear 34C, then gain weight, and correctly measure as 38C but those two bras wouldn’t share the same cup volume. Band and cup must be considered together.

Myth 3: “You can eyeball cup size from photos.”

Fact: Camera angles, padding, push up designs, posture, and image editing (still common in 2026 marketing campaigns) make visual estimation unreliable. What looks like a C cup in one photo might be a DD in an unlined bra. This is why fit depends on measurements, not appearances.

Myth 4: “Once you know your size, it’s universal.”

Fact: Brand to brand and country to country variation means you often vary by 1-2 cups or bands. One manufacturer’s 34D fits differently than another’s. Treat your measured size as an approximate fit starting point, then adjust based on each brand’s specific construction.

Myth 5: “Incorrectly fitted bras are just uncomfortable, not harmful.”

Fact: Chronic wear of poorly fitted bras can contribute to neck pain, shoulder grooving from straps bearing too much weight, and posture issues. A bra that fits properly distributes load through the band, not the straps.

Rely on measurements, fit checks, and trying multiple sizes rather than labels or social media claims. Your body is the authority, not the tag.

Cup size represents volume relative to band size, a letter means nothing without its band number. Measure using the modern “+0” method for accurate results: snug underbust for band, fullest part of bust for cup calculation. Each inch of difference between bust and underbust equals one cup letter (US/UK sizing). Sister sizes share cup volume across different band widths, use them to fine-tune fit. International sizing varies significantly above D cup; always check brand-specific charts. Remeasure every 6-12 months or after body changes rather than assuming your size stays constant. A properly fitted bra has cups that fully contain tissue, a center gore lying flat, a level band, and straps that support, lift, and comfort without digging

Finding your correct cup size is a process, not a one time event. Use this comprehensive list of guidelines as your starting point, try on multiple sizes in each new brand, and trust what feels right on your body. When in doubt, a professional fitting can provide valuable perspective, especially if you’ve been wearing what turns out to be the wrong size for years.