Complete Guide to Full Bust Adjustments (FBA)

If you've ever sewn a bodice that gaps at the neckline, pulls across the bust, or creates strange drag lines, you likely need a Full Bust Adjustment (FBA). This comprehensive guide will walk you through everything you need to know.

What is a Full Bust Adjustment?

A Full Bust Adjustment adds width to a sewing pattern to accommodate a fuller bust. Commercial patterns are drafted for a "B cup" bust, which means if you have a larger cup size, you'll need to add room at the bust while keeping the shoulders, armholes, and waist the same size.

Do You Need an FBA?

Take two key measurements to find out:

| Measurement | How to Measure | |-------------|----------------| | High Bust | Around your torso, under your arms, above your bust fullness | | Full Bust | Around the fullest part of your bust |

The Formula:

Bust Differential = Full Bust - High Bust

• 0-2 inches: You likely don't need an FBA
• 2-4 inches: Small FBA needed
• 4+ inches: Full FBA recommended

The FBA Calculation

Here's how to calculate exactly how much to add:

1. Find your bust differential (Full Bust - High Bust)
2. Subtract the pattern's built-in ease (usually 2 inches)
3. Divide by 2 for each side of the pattern

Example:

• Full Bust: 42 inches
• High Bust: 36 inches
• Differential: 6 inches
• Minus ease (2"): 4 inches
• Per side: 2 inches spread needed

Step-by-Step FBA Process

Step 1: Mark Your Apex Point

The apex is the fullest point of your bust on the pattern. Mark it carefully - this is your pivot point.

Step 2: Draw Slash Lines

Draw two slash lines on your pattern:

1. From the apex to the waist (vertical)
2. From the apex to the armscye (horizontal)

Step 3: Slash and Spread

Cut along the lines and spread the pattern by your calculated amount:

• The vertical line opens at the waist
• The horizontal line opens across the bust

Step 4: True Your Seams

After spreading:

• Redraw the waist seam smoothly
• Adjust the side seam length
• The dart will automatically increase in size

Digital FBA with Bombajom Patterns

The traditional slash-and-spread method works, but it's time-consuming and requires precision. That's why we built Bombajom Patterns - to automate this process digitally.

With Bombajom:

1. Upload your PDF pattern
2. Enter your measurements
3. Mark your apex point
4. Download the adjusted pattern

What takes 30+ minutes by hand takes 2 minutes digitally.

Common FBA Mistakes to Avoid

1. Not using high bust for sizing - Always select your pattern size based on high bust measurement
2. Incorrect apex placement - Take time to locate your actual bust point
3. Forgetting to true seams - Always smooth out cut lines after adjusting
4. Ignoring the dart - The dart intake will increase with an FBA

Next Steps

Ready to try an FBA on your next project? Here are your options:

• Traditional method: Print your pattern, grab scissors and tape, and follow the steps above
• Digital method: Try Bombajom Patterns to adjust your PDF patterns automatically

Have questions about FBA? Check out our measurement guide for more tips on getting accurate measurements.