Choosing Your Pattern Size

Pattern Cup Size vs. Bra Cup Size

One of the biggest sources of confusion when choosing a sewing pattern size is the difference between pattern cup size and bra cup size.

Bra cup size (e.g., 34B, 36D) is based on the difference between your full bust and underbust (ribcage). A Bra cup size is used for sewing intimate apparel like bras, corsets, and very close-fitting garments.

However, sewing patterns use a different system.

Pattern cup size is based on the difference between your full bust and high bust (measured under your armpits, above the bust). Most patterns, including mine, are drafted for a B cup, which means a 2″ difference between high bust and full bust. A sewing pattern cup size is used for fitted and semi-fitted tops, dresses, and garments requiring precise upper body fit.

The High Bust Method to choose your pattern size

For the best fit, especially if you’re a cup size other than B, I recommend using your high bust measurement. This ensures a better fit in the upper chest and shoulder area, which helps prevent gaping or excess fabric.

This pattern is designed for a B cup (2″ difference between high bust and full bust measurements). Follow these steps:

1. Measure your high bust: Wrap measuring tape around your upper chest, just under your armpits and above the fullest part of your bust.
2. Find your size in the chart using your high bust measurement.
3. Compare your actual full bust to the size chart. If there’s a difference, adjust with an FBA or SBA.

Quick Summary:

1. Use your high bust measurement to choose your pattern size.
2. Perform an FBA/SBA to adjust for the difference between your size’s full bust and your actual full bust.
3. Blend/grade at the waist for your size if needed.

Examples:

D Cup Example:

• High bust: 34″
• Full bust: 38″ (4″ difference = D cup)
• Size chart selection: 34″ high bust → Size 8
• Bust difference: 38″ – 36″ (size 8 full bust) = +2”
• Action: Action: Perform a 2” Full Bust Adjustment (FBA) to add room in the bust area while maintaining the correct fit in shoulders and upper chest.

A Cup Example:

• High bust: 34″
• Full bust: 35″ (1″ difference = A cup)
• Size chart selection: 34″ high bust → Size 8
• Bust difference: 35″ – 36″ (size 8 full bust) = -1”
• Action: Perform a 1″ Small Bust Adjustment(SBA) to reduce fullness in the bust area while maintaining proper fit elsewhere.

Remember that making a muslin (test garment) is always recommended to check fit before cutting into your final fabric.

Why Can’t I Just Use My Full Bust Measurement?

If you choose a pattern size based only on your full bust measurement, the rest of the garment—especially the shoulders, neckline, and upper chest—may not fit correctly.

Most patterns are drafted for a B cup (2” difference between high bust and full bust). If your cup size differs, selecting a size based on your full bust can lead to fit issues:

• If you have a larger bust (e.g., D cup or above): The pattern may fit your bust but be too large in the shoulders and upper chest, causing gaping at the neckline or excess fabric in the armhole.
• If you have a smaller bust (e.g., A cup): The pattern may fit your bust but be too tight in the shoulders and armholes, restricting movement and comfort.