Seam allowance explained
The seam allowance is the gap between your stitching line and the cut edge. Patterns tell you how much; 0.6 in (1.5 cm) is common on most dressmaking patterns and 6mm (a quarter inch) in quilting.
Pinny's tip
Check your pattern before cutting. Some patterns include seam allowance and some don't; it changes everything.
Check your pattern before cutting. Some patterns include seam allowance and some don't; it changes everything.
What you'll need
- Seam gauge or ruler: to check the width.
- Needle-plate guide or magnetic seam guide: to sew at a steady width.
- Tailor's chalk: to mark it if you prefer a line.
Step by step
- Read the pattern's instructions or envelope for the seam allowance. Note whether it's included in the pattern pieces.
- Find the matching line on your needle plate (lines are usually in both mm and inches).
- Place the raw edges together and line them up with that guide.
- Sew, keeping the raw edge on the guide all the way.
- Trim, grade or finish the seam allowance afterwards as your pattern says.
Watch
What is Seam Allowance - Sewing Basics (3:21)
By Professor Pincushion · Open on YouTube
The video this technique page has always pointed to, a 3-minute one from Professor Pincushion. Embedded from YouTube with credit; we don't host it. It only loads when you press play.
Common mistakes
- Mixing up allowances between patterns. A 0.4 in (1 cm) seam on a 0.6 in (1.5 cm) pattern adds about 1.6 in (4 cm) round a skirt with four seams (0.5cm on each side of every seam).
- Measuring from the edge of the presser foot. Measure from the needle to the fabric edge, using the plate guide.
- Trimming too early. Leave the allowance until fitting is done so you can let seams out.
Watch it done
- What is Seam Allowance - Sewing Basics by Professor Pincushion on YouTube. Opens on YouTube; the video belongs to its creator.
- What is a Seam Allowance? Sewing Terms - Learn sewing terminology by Evelyn Wood on YouTube. Opens on YouTube; the video belongs to its creator.
Sources
All checked November 1, 2026. We read these; we did not test the products ourselves.
- Tilly and the Buttons: Understanding Sewing Pattern Markings: A Complete Guide
- Stitch and Hem: How to Use a Sewing Machine for Beginners: Your First Hour
- YouTube: What is Seam Allowance - Sewing Basics (Professor Pincushion)
- YouTube: What is a Seam Allowance? Sewing Terms - Learn sewing terminology (Evelyn Wood)