What is a Full Bust Adjustment (FBA)?

An FBA adds width at the bust point of a bodice pattern without changing the shoulders, armhole or waist. It is needed when your bust measurement is larger than the pattern size you selected (based on your high bust measurement).

When do I need an FBA?

Compare your full bust measurement with the pattern. If your bust is 5cm+ larger than the pattern bust for your size (chosen by high bust), you likely need an FBA. The adjustment adds room over the bust and takes it back out at the waist with a larger dart.

A Small Bust Adjustment is the reverse — removing excess bust room when the pattern bust is larger than your body. This is less common but needed when choosing a larger size for shoulder width.

Does this affect dart size?

Yes. An FBA increases the bust dart to accommodate the extra shaping. The dart gets wider by approximately one-quarter of the total bust difference.

SewCalcs

Bust Adjustment Calculator — FBA & SBA

Calculate full bust adjustment (FBA) or small bust adjustment (SBA) for bodice patterns.

Your Bust Measurement

Full bust circumference

Pattern Bust Measurement

Bust on the pattern size chart

Adjustment Type

How We Calculate This

The bust adjustment is calculated from the difference between your body bust and the pattern bust measurement.

The formula

Difference = Body bust − Pattern bust

Per-side adjustment = Difference ÷ 2

Dart increase = Difference ÷ 4

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify quantities before cutting or purchasing fabric.