How to Size for Bras | The Two-Measurement Method

Measuring your ribcage and bust with a soft tape gives you a bra size in about two minutes.

Getting the right bra size comes down to two numbers: your band measurement taken snugly under your breasts, and your bust measurement taken at the fullest point. Subtract the band from the bust, and each inch of difference maps to a cup letter. It’s a straightforward process, but small mistakes in tape placement or tension throw the whole result off. This guide walks through the method step by step, explains how to read the numbers, and shows you how to tell when a bra actually fits.

How to Measure for a Bra at Home

You need a soft measuring tape and a mirror. Measure over bare skin or a non-padded, non-push-up bra — padding adds volume and skews the numbers.

1. Measure your band. Wrap the tape snugly around your ribcage, directly under your breasts. Keep it level and parallel to the floor. Exhale before you read the number so you get your smallest measurement. The tape should feel firm but not tight enough to compress tissue — most guides suggest fitting two fingers under it.
2. Measure your bust. Wrap the tape around the fullest part of your chest, keeping it level across your back and shoulder blades. Don’t pull it tight enough to flatten breast tissue; let it sit against the skin naturally.
3. Subtract to find your cup. Take your band measurement away from your bust measurement. The difference in inches corresponds to a cup letter: 1 inch is an A, 2 inches is a B, 3 inches is a C, and so on.

Your band size comes from the underbust measurement itself. In US sizing, if your underbust is an odd or fractional number, round up to the nearest even whole number — so a 31-inch ribcage becomes a 32 band.

Reading the Numbers and Adjusting the Fit

Once you have your two measurements, you’ll land on a starting size — but it’s only a starting point. Different brands cut their bras differently, and the same person can wear a 34C in one label and a 34D in another.

Here’s how to tell if the size you’re trying is actually right:

• The center gore sits flat. The piece of fabric between the cups should rest against your sternum, not float or tilt.
• Wires stay on your skin. The underwire should follow your breast root and sit firmly against your ribcage, never digging in or lifting off.
• No spillover. Your breasts should be fully contained in the cups with no bulging at the top or sides.
• The band stays level. If the back of the bra rides up, the band is too loose — try a smaller band and a larger cup to keep the same volume.

UK and US conventions use the same inch-based method, but EU and French charts use centimeters and entirely different conversion tables. Always check a brand’s own chart before ordering, since there’s no single universal conversion across all manufacturers.

Bra Size Chart: Turning Inches Into a Size

The table below shows how the inch difference between your bust and band measurements translates into cup letters. Your band size comes from your underbust measurement directly.

Sports bras are the exception to this system. Many use small/medium/large sizing or their own cup-based charts rather than the standard band-and-cup method, so treat a regular bra size as a starting reference only.

Common Measuring Mistakes and What to Do Instead

The most common errors come from tape placement and tension. A twisted tape, a band measured over clothing, or a too-loose bust measurement can shift your result by a full cup size or more. Measure on bare skin, keep the tape level, and take both readings twice to confirm you’re consistent. If your numbers fall between sizes, some guides suggest rounding the band up to the nearest even number and adjusting the cup accordingly.

If your measurements feel off once you try the bra on, trust the fit over the tape. The A Bra That Fits calculator uses several measurements rather than just two, which can help if you’re between sizes or have a shape that standard charts don’t capture well. Once you know your numbers, browsing by size is much easier — our roundup of bras for wide-set small breasts lists options that fit that specific shape well.

Remember that a bra size is a guideline, not a verdict. If a size feels wrong, move up or down a band or cup and try again — the perfect fit is worth the few extra minutes.