Bra Size Chart & Fitting Guide: How to Measure at Home 2025

A Comprehensive Guide to Bra Sizes: How to Measure and Find Your Perfect Fit

 

Bra sizing can seem confusing at first glance—but with the right measurements and a basic understanding of how cup and band sizes work, finding your perfect bra size is easier than you think. This detailed guide walks you through everything you need to know about bra size charts, how to measure bra size at home, and understanding cup size differences—so you can shop smarter and feel supported every day.

Bra sizing — is it really as easy as learning your ABCs and 123s? Well, maybe not quite child’s play, but we can certainly help demystify this somewhat complicated system, which tends to vary from style to style and even brand to brand, especially when it comes to European manufacturers.

What Do Bra Sizes Mean?

A standard bra size consists of two parts:

• A number (like 32, 34, or 36) indicating the band size

• A letter (like A, B, C, or D) representing the cup size

In the U.S., bra cup sizes typically range from AA to K or higher, with increments reflecting 1-inch differences in bust-to-band measurements. Meanwhile, band sizes usually start at 28 or 30 and increase in even numbers: 32, 34, 36, and so on.

Understanding this alphanumeric system is the first step toward finding a well-fitting bra.

In the simplest terms, the U.S. uses letters A through F and so on, to represent cup size with incremental increases in volume the further up you go. Multiple lettering, such as AA and DDD, is part of the nuanced system too, which we’ll get into later. A bra’s numerical value indicates its band size, a calculation in inches based on the measurement around a woman’s torso just under her breasts. These numbers typically start at 30 and increase by twos: 32, 34, 36… you get the idea.

So how do you navigate this alphanumeric roadmap? Let’s start with an overview of the most common sizing available from a wide variety of retailers.

How to Measure Your Bra Size at Home

All you need is a soft measuring tape and a lightly lined bra to get started. The two essential numbers you’ll need are:

1. Under-Bust Measurement (for Band Size)

• Wrap the tape snugly around your ribcage directly beneath your breasts.

• Make sure the tape is level and flat against your body.

• Round the number to the nearest whole number.

• If it's even, add 4 inches. If it's odd, add 5 inches. This is your band size.

Example:
If your under-bust is 30", add 4 = 34 band size
If your under-bust is 31", add 5 = 36 band size

Start by wrapping the tape measure around the torso just beneath the breasts. The tape should rest flat against the body, running parallel to the bottom edge of your bra band. If the measurement falls between whole numbers, round up. Add four inches to the number if it happens to be even; add five if it turns out odd. This is your band size. For example, with an under-bust number of 30, the expected band size will be a 34, whereas a 31-inch measurement would give you a band size of 36. Getting an accurate number will help ensure your bra fits snugly to support breasts, however, it won’t be so tight that it’ll cut into skin or inhibit your ability to easily move and breathe. Because underbands naturally stretch out over time, remember to hook your bra closed on the loosest setting and only increase the tension with repeated wear.

2. Bust Measurement (for Cup Size)

• Measure around the fullest part of your bust, keeping the tape level.

• Subtract your band size from your bust measurement to find the difference.

3. Use the Cup Size Chart Below

Example:
Bust = 39", Band = 34" → 39 - 34 = 5 → 34DD bra size

The next measurement you’ll need will be the fullest part of the bust. To determine this, simply wrap the tape measure around breasts where they protrude most, making sure to keep the ribbon flat and parallel to your bra’s underband. The difference in inches between the breast and under-bust will be what determines your cup size. Knowing this, you’ll have an accurate sense of the volume needed to avoid overflow or gaping, which happens when you’re wearing a cup that’s too small or too large for your chest.

Understanding Cup Size Differences

Contrary to common belief, a DD cup does not mean “double D” volume. Instead, it’s a standard size, indicating a 5-inch difference between the band and bust. Additional letters like DDD or E, F, and beyond represent increasing cup volumes.

Each inch in difference corresponds to the next cup size. A DDD is simply one step above DD.

So, how do you know what cup size you are? Every letter grade is equivalent to the difference of one inch between the breast and under-bust calculations, starting with an A. That means a two-inch difference will result in a B cup, a three-inch difference is a C, and so on up through the alphabet. You might think that multi-letter sizes such as DD represent that cup volume, doubled — a common misconception, but these sizes are actually just midpoints between letter grades. As an example, a DD is a cup that falls halfway between a D and an F, reflecting a five-inch difference between a woman’s breast and under-bust measurements. Once you have your numbers tallied, you can apply this sizing know-how to any style bra, keeping in mind that oftentimes, slight variations will occur from one manufacturer to another. Trying on a few bras within your size range to determine which fits your body shape best is always recommended, as is exploring the concept of sister sizing.

Sister Sizing: What Is It?

Sister sizes refer to alternate sizes that have the same cup volume but different band sizes. For example:

• 34D, 36C, and 32DD are sister sizes.

If your usual bra size feels too tight in the band but fits in the cups, go up a band size and down a cup size. If it’s too loose, do the opposite.

Standard Sizing vs. Numerical Bra Sizes

For some types of undergarments, like unstructured bras, tanks and bodysuits, manufacturers may choose to go the grouped sizing route, similar to the standards used in clothing. These include: small, medium and large, with XS and XL bookending each side of the range, as well as plus sizes of 1X, 2X and so on. The groupings are based on the band’s width rather than cup’s volume, meaning that letter grades are less relevant in this type of sizing. With standard sizing, you can expect a 32C and a 32D to be bracketed together as a Small, a 34C and a 34D to both be Medium, a 36C and 36D to equate a Large, and so on, up through the fit range.

In many wireless bras, camisoles, and bodysuits, you may see standard sizing: XS, S, M, L, XL, etc.

These sizes are grouped based on band measurements, not cup volume. Here’s a rough conversion chart:

Why Your Bra Size Can Change

Even with the most accurate measurements, bra sizes can change due to:

• Weight gain or loss

• Pregnancy or nursing

• Hormonal changes

• Aging or natural shifts in breast tissue

That’s why it’s important to re-measure your bust and under-bust every 6–12 months or whenever you feel your bra no longer fits well.

Final Tips for the Perfect Fit

• Start with the loosest hook on new bras — this gives you room to tighten as the elastic stretches over time.

• Adjust straps individually — one may need to be tighter than the other.

• Check the center gore — it should lie flat against your sternum.

• Replace bras every 6–12 months, especially if worn frequently.

 

In Summary