4 – Beginner Draping: How to Add Seam Allowance to a Pattern Piece

You’ve got your pattern drafted to paper, what’s next? Seam allowance! The area of extra room from the sewn edges to the raw edges of the fabric is referred to as seam allowance. It affects the final size of the cut pieces, while allowing a bit of fraying room without affecting the overall construction of the garment. Most garments will call for an allowance of 1/4″, 1/2″ or 5/8″ but the amount varies depending on the pattern and fabric type. Additionally, seam allowance is usually consistent throughout a project but in special cases the amount of seam allowance may also vary depending on the fabric and pattern design. 

Purchase tools we use:

• Prepped Muslin Block (pressed & transferred to paper)
• Pattern Paper
• Clear Ruler
• French Curve (optional)
• Marking Tool

First determine whether or not your seam allowance has already been included. Commercial patterns typically include seam allowance, but seam allowance will need to be added to printable patterns and self drafted patterns.

If you are sewing a manufactured pattern the seam allowance is commonly added in, which means you just have to check that all seam allowance is consistent, transfer all lines and marks to fabric, then you can begin sewing by lining up your sewing machine SA guides with your fabric. 

To add seam allowance to regular seams (non-regular seams include “cut on fold” sides and hemlines).

1. Choose your seam allowance amount 
2. Lay your marked pattern paper down 
3. Use a straight-edge ruler and french curve to measure out the seam allowance around all side and shoulder seams, marking curves with dashed lines as you go
4. Connect dashes once you have measured all regular seams

To add seam allowance to the hemline if the amount isn’t already given:

1. Choose a seam allowance of about ¾”
2. Follow the remainder of the steps from above (you will only need a straight edge ruler)

To add seam allowance to angled pieces:

1. Choose your seam allowance
2. Measure around the angled area ensuring that the corner is angle out when being cut, this prevents the corner from becoming narrow once it is folded

Take your drafted pattern to the next level by using our post to add seam allowance so you can get sewing. Seam allowance will keep frayed edges at bay, and additionally allow a little extra room for alterations and once you add seam allowance once, you’ll quickly realize how easy, yet important it is. Grab your front and back bodice and add your seam allowance to get started!